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D I R Y P R O D U C T I O N
E n e rg y M e ta b o l i s m o f D a i ry C a t t l e
P . W . M O E 1
US Department of Agriculture
B e l t s v i l l e
MD 2 7 5
A B S T R A C T
E n e r g y m e t a b o l i s m r e s e a r ch d u r i n g t h e
p a s t 2 5 y r h a s r e s o lv e d m a n y u n c e r t a i n t i e s
o f e n e r g y u s e b y l a c t a t i n g c o w s . U s e o f
m e t a b o l i z a b l e e n e r g y f o r m i l k p r o d u c t i o n
e s s e n t i a l l y is u n a f f e c t e d b y m i l k y i e l d b u t
i s s l i g h t l y i n f l u e n c e d b y i t s s o u r c e .
E s t i m a t e s o f e f f ic i e n c y o f u s e f o r m i l k
p r o d u c t i o n ( 6 0 t o 6 4 % ) a r e l o w e r t h a n
e a r l i e r e s t i m a t e s (6 9 t o 7 0 % ) p r i m a r i l y
b e c a u s e o f l o w e r m a i n t e n a n c e c o s t s .
E f f i c i e n c y o f m e t a b o l i z a b l e e n e r g y f o r
b o d y g a i n i s h i g h e r i n l a c t a t i n g (75 )
t h a n n o n l a c t a t i n g ( 6 0 % ) c o w s . U s e
o f b o d y t i ss u e e n e rg y f o r m i l k p r o d u c t i o n
i s a b o u t 8 2 % e f f i c i e n t . E n d p r o d u c t s o f
d i g e s t i o n c o n t r i b u t e t o v a r i a t i o n i n
e f f i c i e n c y o f f a t t e n i n g a n d i n p a r t i t i o n o f
e n e r g y b e t w e e n m i l k a n d b o d y g a i n i n t h e
l a c t a t i n g a n i m a l .
E n e r g y u s e i n t h e g r o w i n g a n i m a l is
i n f l u e n c e d b y c o m p o s i t i o n o f t is s u e
g a i n ed a n d c o m p o s i t i o n o f t h e d i e t.
E n e r g e t i c e f f i c i e n c y o f p r o t e i n d e p o s i t i o n
i s a p p a r e n t l y m u c h l o w e r t h a n t h a t o f f a t
d e p o s i t i o n . A s u b s t a n t i a l p a r t o f t h e
l o w e r e f f i c i e n c y o f p r o t e i n d e p o s i t i o n is
r e l a t e d t o e n e r g y c o s t s o f p r o t e i n t u r n o v e r .
I n c o m p l e t e d i g e s ti o n o f m i x e d d i e ts a t
h ig h i n t a k e b y l a c t a ti n g c o w s a n d m e t h o d s
t o p r e d i c t e n e r g y p a r t i t i o n a r e s e r i o u s
p r a c t i c a l p r o b l e m s . I n t h e s h o r t t e r m ,
i m p r o v e d m e t h o d s t o p r e d i c t i n t a k e
e f fe c t s o n m e t a b o l i z a b l e e n e r g y o f m i x e d
d i e t s w i l l i n c r e a s e a c c u r a c y o f d i e t
f o r m u I a t io n s . I n th e l o n g e r te r m , m e t h o d s
t o p r e d i c t q u a n t i t ie s o f n u t r i e n ts a b s o r b e d
f r o m t h e g u t w i l l p e r m i t a m o r e f l e x i b l e
a n d a c c u r a t e m e t h o d o f e v a l u a t i n g d ie t s
a n d p r e d i c t i n g a n i m a l p e r f o r m a n c e .
Received June 26, 1980.
1 Rum inan t Nutr i t ion Labora to ry , Animal Sc ience
Insti tute, A gricultural Research, Science and Edu cation
Ad min istration, US DA , Beltsville, MD 20705.
I N T R O D U C T I O N
In 1955 B t a x t e r a n d G r a h a m ( 2 3 ) s ta t e d , I n
t h e p e r i o d s i n c e K u h n a n d K e l l n e r , t h e c o n -
s o l i d a t i o n a n d e x t e n s i o n o f t h e n e t - e n e r g y
p r i n c i p l e , w h i c h m i g h t h a v e b e e n e x p e c t e d t o
h a v e o c c u r r e d a s a r e s u l t o f s u c h b r i l l i a n t w o r k ,
h a s , w i t h s e v e r a l n o t a b l e e x c e p t i o n s , n o t t a k e n
p l a c e . I n s t e a d , t h e p e r i o d h a s b e e n c h a r a c t e r i z e d
b y p o l e m i c a l a r g u m e n t r a r e l y i l l u m i n a t e d b y a n
e x p e r i m e n t a n d h a r d l y e v er b y a c a l o r i m e t r i c
t r i a l . K e l l n e r ' s o r i g i n a l w o r k h a s b e e n r e c a l -
c u l a t e d , r e - e x p r e s s e d a n d , i n s h o r t , s u c k e d d r y .
. . C l e a r l y , i n t h e a s s e s s m e n t o f t h e n u t r i t i v e
v a l u e o f f o o d s , t h e f u t u r e m u s t i n v o l v e e x t e n s i v e
e x p e r i m e n t a t i o n a n d m e a s u r e m e n t r a t h e r t h a n
t h e a l m o s t c o m p l e t e d e p e n d e n c e on p i o n e e r
e v i d e n c e w h i c h h a s c h a r a c t e r i z e d th e p a s t 5 0
y e a r s .
P r o g re s s h a s b e e n c o n s i d e r a b l e i n t h e f i e l d o f
e n e r g y m e t a b o l i s m s i n c e t h o s e w o r d s w e r e
w r i t t e n E f f i c i e n c y o f e n e r g y u s e a n d e n e r g y
r e q u i r e m e n t s h a v e b e e n i d e n t i f ie d m o r e p r e -
c i s e l y . P r o g r e s s i v e l y m o r e i n t e n s i v e e x p e r i -
m e n t a t i o n h a s d e s c r i b e d p h y s i o l o g i c a l a n d
b i o c h e m i c a l b a s e s f o r a n i n c re a s i n g p a r t o f t h e
v a r i a t i o n i n e n e r g y u s e . A l t h o u g h e n e r g y
m e t a b o l i s m h a s b e e n s t u d i e d a t m a n y l ev e ls
f r o m s p e ci fi c b i o c h e m i c a l t r a n s f o r m a t i o n s t o
w h o l e p o p u l a t i o n s o f a n i m a l s , t h i s r e v i e w w i l l
d e a I p r i m a r i l y w i t h e n e r g y u s e i n t h e w h o l e
a n i m a l. A s p e c t s o f e n e rg y m e t a b o l i s m t h a t
r e l a t e to t h e e f f e c t i v e n e s s w i t h w h i c h d a i r y
c a t t l e c o n s u m e a v a r i e t y o f d i e ts f o r g r o w t h ,
r e p r o d u c t i o n , a n d p r o d u c t i o n o f m i l k w il l b e
c o n s i d e r e d .
E n e r g y T e r m i n o l o g y
I n t h e d i s c u s s i o n , t e r m i n o l o g y i s t h a t i n
g e n e r a l u s e . D i g e s t i b l e e n e r g y ( D E ) i s g r o s s
i n t a k e o f e n e r g y m i n u s e n e r g y v o i d e d in t h e
f e ce s . M e t a b o l i z a b l e e n e r g y ( M E ) i s D E m i n u s
e n e r g y i n m e t h a n e a n d u r i n e . Generally M E i s
a n e x p r e s s i o n o f t h e a m o u n t o f e n e r g y a v a i l a b l e
f o r m e t a b o l i s m b y t h e a n im a l , a l th o u g h M E
i n c l u d e s s o m e e n e r g y , e .g . , h e a t o f f e r m e n t a t i o n ,
1981 J Dairy Sci 64 :112 0-1 139 11 20
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ME T ABOL I SM - - 7 5 T H ANNI VE RSARY I SSUE 1 1 2 1
n o t a v a il a b le f o r m e t a b o l i s m a n d d o e s n o t
i n c l u d e s o m e e n e r g y , e . g ., u r i n e e n e r g y , w h i c h
i s a p r o d u c t o f m e t a b o l i s m . T h e t e r m s f o r t h e
p a r t i a l e f f i c i e n c y o f M E u s e d f o r m a i n t e n a n c e ,
l a c t a t i o n , p r o t e i n g a i n , f a t g ai n , a n d g a i n i n
t o t a l t i s s u e e n e r g y a r e k i n , k l , k p , k f , a n d k g .
H e a t i n c r e m e n t ( H I ) is t h e i n c r e a s e in t o t a l p r o -
d u c t i o n o f h e a t a s s o c i a t e d w i t h a n i n c r e a s e i n
t h e c o n s u m p t i o n o f f o o d .
E n e r g y u n i t s a r e c a l o r i e s ( c a l) , k i l o c a l o r i e s
( k c a l = 1 0 0 0 c a l ), o r m e g a c a l o r i e s ( M c a l = 1 0 0 0
k c a l ) f o r t h e c o n v e n i e n c e o f t h e U S r e a d e r
a l t h o u g h m a n y o f t h e o ri g i n a l p a p e r s i n c l u d e d
t h e j o u le ( 1 c a l = 4 . 1 8 4 J ; J = M 2 . k g . s - 2 ) .
T h e S i t u a t i o n 5 Ye a rs A g o
R e v i e w s b y B l a x t e r (1 4 , 1 5 ) a n d R e i d
77,
7 8 ) a n d m a j o r t e x t s b y B l a x t e r ( 1 7 ) a n d K l e i b e r
( 4 7 ) s u m m a r i z e d m u c h o f t h e w o r k o n e n e r g y
m e t a b o l i s m o f d a i r y c a t t le a n d p r e s e n t t h e m o s t
c o m p r e h e n s i v e d e s c r i p t io n s o f t h e e n e r g e ti c s o f
d a i r y c a t t l e a v a i l a b le in t h e i r t i m e . E a r l i e r
s t u d ie s s h o w e d t h a t l a c t a t i o n w a s m o r e e f f i c ie n t
t h a n f a t t e n i n g . R e i d ( 7 8 ) s u m m a r i z e d t h e
a v a i l a b l e c a l o r i m e t r y d a t a a n d c o n c l u d e d t h a t
M E c o n s u m e d i n e xc e s s o f m a i n t e n a n c e w a s
u s e d t o t h e e x t e n t o f 6 9 .3 f o r m i l k p r o d u c t i o n
a n d 5 8 .0 f o r b o d y i n c r e a s e a n d t h a t b o t h
w e r e r e l a t iv e l y c o n s t a n t . G r o w t h w a s t h o u g h t
t o b e m o r e e f f i c i e n t t h a n f a t t e n i n g . E n e r g y
f r o m g r a i n s o r c o n c e n t r a t e f e e d s g e n e r a l l y w a s
a c c e p t e d t o h e u se d m o r e e f f i c i e n tl y th a n
e n e r g y o f f o r a g e s, e s p e c i a l l y f o r g r o w i n g
a n i m a l s . T h i s d i f f e r e n c e a p p e a r e d t o b e r e l a t e d
t o t h e c r u d e f i b e r c o n t e n t o f t h e f o r a g e .
C o n s i d e r a b l e d i s a g r e e m e n t e x i s t e d r e g a r d in g
t h e r e l a t i o n s h ip b e t w e e n e n e r g y i n t a k e a n d
e n e r g y b a l a n c e ( E B ) . W o r k e r s g e n e r a l l y a c c e p t e d
t h a t t h i s r e l a t i o n s h i p w a s c u r v i l i n e a r w h e n d a t a
b o t h a b o v e a nd b e l o w m a i n t e n a n c e w e r e
i n c l u d e d . B l a x t e r (1 5 ) e m p h a s i z e d t h e c u rv i l i n a r
r e l a ti o n s h i p b e t w e e n f o o d c o n s u m e d a n d
e n e r g y r e t e n t i o n a n d i n d i c a t e d t h a t t hi s e ff e c t
w a s a t l e a s t in p a r t f r o m a d e c l i n e in M E v a l u e
w i t h i n c r e a s e d i n t a k e .
A l t h o u g h w o r k h a d d o c u m e n t e d r e d u c e d
d i g e s t i b i l i t y b y l a c t a t i n g c o w s i n c o m p a r i s o n
w i t h t h a t o f c o w s a t m a i n t e n a n c e i n t a k e ,
t h i s e f f e c t w a s n o t a c c e p t e d u n i v e r s a l l y . R e i d
( 7 8 ) e m p h a s i z e d t h e i m p o r t a n c e o f r e d u c e d
d i g e s t i b il i t y a n d i n c r ea s e d b o d y f a t t e n i n g
b y l a c t a t i n g c o w s a t h i g h f e e d i n t a k e s i n e x -
p l a i n in g a p p a r e n t d i m i n i s h i n g r e t u r n s i n f e e d i n g
t r ia l s w i t h l a c t a t i n g c o w s .
C o n s i d e r a b l e u n c e r t a i n t y r e m a i n e d w i th
r e g a r d t o t h e e f f e c t o f d i e t q u a l i t y o r r a t e o f
m i l k p r o d u c t i o n o r r a te o f g r c w t h o n e f f ic i e n c y
o f u se o f M E a n d w h e t h e r d i e t e f fe c t s w e r e
s i m i l a r f o r f a t t e n i n g a n d m i l k p r o d u c t i o n .
T h e s e q u e s t i o n s w e r e o f f u n d a m e n t a l i m -
p o r t a n c e i n p r o v i d i n g a c c u r a t e a n d u s e f u l
f e e d i n g s t a n d a r d s .
T h e s i t u a t i o n i n 1 9 56 c a n b e u n d e r s t o o d
m o s t a d e q u a t e ly b y r e m e m b e r i n g t h a t th e
l i m i t e d c a l o r i m e t r i c d a t a o n l a c t a t i n g c o w s
a t t h e t i m e h a d b e e n o b t a i n e d m a n y y e a r s
p r e v i o u s l y . T h o s e r e s u lt s , a l t h o u g h i m p o r t a n t
a n d a l t h o u g h o b t a i n e d w i t h p r e c i s e m e t h o d s ,
w e r e i n a d e q u a t e t o a n s w e r i m p o r t a n t q u e s t i o n s
r a i s e d a b o u t f a c t o r s a f f e c t i n g e f f i c i e n c y o f
e n e r g y u s e b y c a t t l e . T h o s e r e s u l t s w e r e r e -
c a l c u l a t e d a n d d e b a t e d i n t h e l i g h t o f n e w e r
k n o w l e d g e . N e w i n t e r p r e t a t i o n s w e r e p u t
f o r w a r d w i t h o u t b e n e f i t o f f a c il i ti e s t o t e s t
t h e i r v a l id i t y . N e w e x p e r i m e n t a t i o n w a s n e e d e d .
The Last 5 Years
T h e 2 5 y r s in c e 1 9 5 6 c o i n c i d e s a l m o s t
e x a c t l y w i t h a n e x c e p t i o n a l b u r s t o f e x pe r i -
m e n t a t i o n i n a n i m a l e n e r g e t i c s . I n t h e l a t e
1 9 5 0 's , m a j o r c o m m i t m e n t s t o s u p p o r t e n e r g y
m e t a b o l i s m r e s e a r c h w e r e m a d e i n a n u m b e r o f
c o u n t r i e s i n c l u d i n g t h e U S . T h e i n c r e a s e i n r a t e
o f e x p e r i m e n t a t i o n w i t h l a c ta t i n g c o w s c an b e
a p p r e c i a t e d f r o m t h e f a c t t h a t a t o t a l o f 1 1 0
c o m p l e t e e n e r g y b a l a n c e t r i a l s w i t h 3 8 c o w s ,
i n c l u d i n g a l l r e p l ic a t e s , h a d b e e n c o m p l e t e d i n
a l l o f t h e l a b o r a t o r i e s i n t h e w o r l d b e f o r e 1 9 6 1
( 3 4 ) . S i n c e t h a t t i m e t h e r e s u lt s o f 8 0 6 b a l a n c e
t r i a l s w i t h l a c t a t i n g c o w s h a v e b e e n p u b l i s h e d
f r o m t h e B e l t s vi l le l a b o r a t o r y a l o n e . T o c o -
o r d i n a t e t h e i n c r e a s e d r e s e a r c h a c t i v i t y a n d t o
s h a r e r e s e a r c h p l a n s a n d r e s u l ts , a n I n t e r n a t i o n a l
S y m p o s i u m o n E n e rg y M e t a b o li s m w as h e l d
i n C o p e n h a g e n i n 1 9 5 8 u n d e r t h e s p o n s o r s h i p
o f t h e E u r o p e a n A s s o c i a t i o n o f A n i m a l P r o-
d u c t i o n ( E A A P ) . S u c c e e d i n g s y m p o s i a , h e l d
e v e r y 3 y r , h a v e p r o v i d e d a c o n t i n u i n g f o c u s f o r
e n e r g y m e t a b o l i s m r e s ea r ch . T h e p r o c e e d i n g s o f
t h e s e s y m p o s i a , p u b l i s h e d b y t h e E A A P ,
d o c u m e n t a s u b s ta n t i a l p a r t o f t h e e n e r g y
m e t a b o l i s m r e s e ar c h w i t h f a r m a n i m a l s d u r i n g
t h e l a s t 2 5 y r ( T a b l e 1 ) .
T h e s y m p o s i a i n 1 9 5 8 a n d 1 9 6 1 d e a l t l a r g e l y
Journa l of D airy Science Vol. 64, No. 6 , 1981
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1122 MOE
TABLE 1. Symposia on energy metabolism sponsored by the European Association of Animal Production
(EAAP).
1st
2nd
3rd
4th
5th
6th
7th
8th
Symposium on Energy Metabolism. Principles, Methods, and General
Aspects. Copenhagen, Denmark. 15 -19 September 1958. Publ. by EAAP
(Publ. No. 8) and Statens Husdyrugsudvalg, Copenhagen. Grete Thorbek
and H. Aersoe, ed.
Symposium on Energy Metabolism. Methods and Results of Experiments
with Animals. Wageningen, the Netherlands. 11-15 September 1961.
EAAP Publ. No. 10. E. Brouwer and A.J.H. van Es, ed.
Symposium. Troon, Scotland. May 1964 . Energy Metabolism. Publ.
by Academic Press, New York and London. 1965. K. L. Blaxter, ed.
EAAP Publ. No. 11.
Symposium. Energy Metabolism of Farm Animals. Warsaw, Poland. Sep-
tember 1967. Publ. by Oriel Press, Newcastle upon Tyne, England. 1969.
K. L. Blaxter, J. Kielanowski and Grete Thorbek, ed. EAAP Publ. No. 12.
Symposium. Vitznau, Switzerland. September 1970. Energy Metabolism
of Farm Animals. Juris Verlag, Zurich. A. Schurch and C. Wenk., ed.
EAAP Publ. No. 13.
Symposium. Hohenheim, B.D.R. September 1973. Energy Metabolism
of Farm Animals. Publ. by Universitat Hohenheim Dokumentationsstelle.
1974. K. H. Menke, H. J. Lantzsch, and J. R. Reichl, ed. E A A P Publ.
No. 14.
Symposium. Vichy, France. September 1976. Energy Metabolism of
Farm Animals. Publ. by G. de Bussac, Clermont-Ferrand. M. Vermorel,
ed. E A A P Publ. No. 19.
Symposium. Cambridge, England. September 1979. Energy Metabolism.
Publ. by Butter worths, London. 1980. EAAP Publ. No. 26. L. E. Mount, ed.
with method ology: construction of respiration
chambers, tech niqu es o f gas analysis, and
potential errors in energy balance measurements.
Succeeding symposia dealt increasingly with
presentation of results of animal experiments,
discussion of interpre tations of energy balance
measurements, and proposals for application of
findings in practice including discussions on
feed evaluation and feeding standards. More
recent symposia have dealt progressively less
with feed evaluation and increasingly with
specific factors limiting or causing variation in
energy use by farm animals including more
intensive and physiological experi mental ap-
proaches and newer methods of describing and
interpreting data.
Major advances during this time have been in
identifying und etec ted sources of variation in
energy use, in developing quantitative des-
criptions of known sources of variation, and in
developing recommendations for means of
implementing knowledge of energetics in
practical feeding systems.
f f ec t s o f b s o r b e d N u t r i e n t s
E n e r g e t i c ~ f f i c i e n c y A major improvement
in understan ding the causes of variation in
energy efficiency of animals fed different
diets was the demon strat ion of Armstrong,
Blaxter, and their coworkers (2, 3, 4, 6, 7) that
the heat increment of mixtures of steam
volatile fatty acids (VFA) was influenced
greatly by the propo rtion of acet ate in the
fattening sheep but had less effec t in sheep at
maintenance. The energy of VFA infused singly
into the rumen of fattening sheep was used
with efficien cies of 32.9 for acetic acid,
56.3 for pro pion ic acid, and 61.9 for
butyric acid. Mixtures o f VF A containing 75
and 25 acetic acid were used with 31.8 and
58.1 efficiency. Other studies showed a lower
efficiency (54.5 ) for glucose infused into the
rumen than for that infused into the abomasum
(71.5 ) or jugular vein (72.8 ). These studies
indicated the importance of end products of
digestion as opposed to nutrients consumed in
influencing metabolic efficiency in ruminants.
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METABOLISM -- 75TH ANNIVERSARY ISSUE 1123
These studies also suggested that vari ation in
the efficiency with which specific end products
of digestion are metabolized could account for
a substantial part of the apparent difference
between use of fibrous diets and that of diets
contai ning large amou nts of starch. The ap-
parently low efficiency of acetate use in the
fattening animal appeared to account for the
depression in net energy of feeds high in fiber
that had caused Kellner to intr oduce his fiber
correct ion fact or some 50 yr earlier.
More recent experiments indicated that the
proportion of acetate of the rumen fermentatio n
products may n ot explain fully the variation in
use of ME and that in some circumstances
acetate ma y be used efficiently for body gain.
Tyrrell et al. (92) reviewed several experiments
in which acetate apparently was used with
relatively high efficiency for body gain and
reported the results of calorimetric investi-
gations with VFA infusion in mature cows.
They found a difference from the nature of the
basal diet in the partial efficiency of acetate for
body gain. Use of ME from infused acetic acid
was 27% for cows fed 100% hay and
69
for
cows fed a diet of 30% hay.
Orskov et al. (71) reported experiments in
which lambs were sustained entirely by in-
tragastric infusion of VFA, protein, minerals,
and vitamins. For mixtures of VFA with 450 to
750 mmol acetate/mol, efficiency of use was 57
to 64%. They also recalculated the earlier data
of Armstrong and Blaxter and reported that
those results predicted an efficiency of 44 to
50%. Orskov et al. (71) concluded that the
effect of proportion of acetate on efficiency of
energy use in growing animals was, in both
instances, too small to be of practical signifi-
cance.
The differences in the results of Tyrrell et al.
(92) and Orskov et al. (71) remain unresolved.
A partial explanation may be found in the
differing physiological state of the e xperimen tal
animals. Data of Orskov et al. (71) pertain to
growing lambs depositing substantial protein
whereas data of Tyrrell et al. (92) pertain to
fattening in adult cows. Under some conditions
acetate is used with low efficiency for fatt ening
although some questions remain as to exactly
what those conditions are. Also, acetate can be
used efficiently in many instances, especially
with high concent rate diets.
Parti tioning o f Energy.
In only a relatively
few experime nts has the use of individual VFA
in lactation been investigated. Armstrong
and Blaxter (5) in calorimetric studies infused
mixtures of VFA, propionate, and acetate into
the rum en of goats and found efficiencies of
71.4, 72.3, and 65.0% for lactation and 50.3,
52.3, and 44.4% for energy retention in the
nonlactating body. Two particularly important
findings were described in this paper. First,
acetic acid inf usi on resulted in an increase in
milk fat secretion and a decline in body fat
deposition whereas with pro pionic acid infusion
the reverse was true. Second, heat production
was no t changed. This second findi ng led them
to the con clusion that energy reten tion in the
adult ruminant is more efficient accompanied
by the simult aneous process of milk secretion
than in the nonl actat ing animal. The effect of
VFA infusion on energy partition was noted
with lactating cows by Orskov et al. (70) in
calorimetry experiments. Acetic acid infusion
resulted in more milk energy and less gain of
body energy than did propionic acid infusion.
No difference in efficiency was found.
Effects on energy partition in lactation have
been similar with changes in diet. Table 2 shows
results of an experiment by Flatt et al. (36, 37)
in which cows fed a 60:40 ratio of forage to
concentrate produced more milk and lost more
body tissue energy than cows fed a 20:80 ratio.
The ratio of acetate to propio nate in rumen
VFA was also higher on the higher forage diet.
In incremental studies of corn grain and beet
pulp, Tyrrell et al. (89) found a greater per-
centage of the increase in energy balance (milk
plus body tissue) was milk when beet pulp was
added to the diet than when corn was added.
Sutton et al. (82) observed a reduction in
proportion of acetate in rumen VFA and a
reduction in milk fat yield by lactating cows
when the percentage of concentrate was in-
creased from 60 to 90%. At 90% concentrate,
more starch reached the duodenum when
corn grain was fed than when barley was fed.
Live weight gain was also greater on the 90%
corn diet, and milk yield was less. When corn
replaced barley, the contribution of rumen
digestion to overall digestion of energy was
reduced considerably.
Effects of percentage concentrate, percentage
of crude protein, and feed intake on partition
of energy in lactating cows were studied by
Journet et al. (44). The partition of energy into
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1124 MOE
TABLE 2. Influence of hay:grain ratio on partition of energy between milk and body tissuea.
Hay:grain ratio
Item 60:40 40:60 20:80
Metabolizable energy (ME) intake, Mcal 36.12 36.42 34.87
Energy balance, McaI 11.94 12.63 12.16
Milk energy, Mcal 13.94 13.17 10.41
Tissue energy, Mcal - 2.00 - . 54 1.75
Milk fat, 3.5 3.0 2.7
Acetic:propionic 3.32 2.57 2.00
aData from Flatt et al. (36, 37).
milk decreased with increasing percentage of
concentrate and decreasing percentage of milk
fat. They also found that when energy intake
varied around the requirement, about one-third
of the increment of energy went into milk and
two-thirds into body gain. No relationship
between major VFA and milk production was
found, but minor VFA (isobutyric, isovaleric,
and valeric) in the rumen and crude protein in
the diet were related positively to milk pro-
duction.
Variation in the partial efficiency of use of
the energy of VFA is considerably more im-
portant in fattening than in lactation whereas
the effect in the growing animal is less certain.
In the lactating cow, however, amounts of
individual VFA absorbed from the gut can
exert a significant effect on partition of energy
between milk and body tissue. Effects of
variation in amount and type of diet on energy
efficiency and energy partition likely will not
be explained satisfactorily without compre-
hensive knowledge of amounts of specific
nutrients which are absorbed from the digestive
tract.
In ta k e a n d s s o c ia t iv e Ef fe c ts
In take E f fects Although intake effects on
digestibility had been shown early in this
century (29, 41), the practical significance
of this effect by no means was accepted uni-
versally. The question was debated at a sym-
posium in 1965 (26, 34, 76, 79). Brown (26)
cited several instances in which intake effects
on digestibility appeared to be conflicting. He
concluded that although reduced digestibility
had been detected at high intakes of diets
containing large amou nts of concentrates in a
numbe r of experiments, additional inform ation
was needed. Flatt (34) reviewed the information
then available on intake effects on ME value of
diets and concluded that such an effect could
not be documented. In a study of Beltsville
data, Moe et al. (54) also found no intake effect
on ME values of diets conta ining 40, 60, and
80 conce ntrat e for lactating cows. Not unti l
the 1970's did experime ntal results begin
to appear to indicate in a relatively systematic
fashion that ME values of diets for lactating
cows were substant ially lower than the same
diets fed to nonl actating cows at a maintenan ce
intake.
The significance of depression in digestibility
of diets at high int akes by lactati ng cows was
established firmly in extensive digestibility
measurements by Moe et al. (56), Wagner and
Loosli (103), and Ekern (31). Tyrrell and Moe
(86) reviewed these and other studies and
concluded that digestibility of normal diets by
dairy cows was reduced by abo ut 4 for each
increase in intake equivalent to the amount
needed for maintenance. They also concluded
that the rate of redu ctio n in digestibility was
greater for diets containi ng larger percentages
of concentrate although this effect was less
pronounced for diets based on corn silage.
Intake effects are as great with corn silage-based
diets as with other forages when high per-
centages of grains are fed. At lower percentages
of grain, however, intake effects are likely
greater with corn silage diets than for those
cont aini ng other forages.
In a more recent review, Tyrrell (85) cites
evidence that the digestibility of corn silage-
based diets is improved by addition of ground
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METAB OLISM - - 75TH ANNIVERSARY ISSUE 11 25
l i m e s t o n e t o t h e d i e t ( 1 0 9 ) o r b y i n c r e as e d
p r o t e i n c o n t e n t ( 7 4 ) a n d i n a l f a l f a - b a s e d d i e t s
b y i n c r e a s e d p r o t e i n c o n t e n t ( 8 8) .
T y r r e l l a n d M o e ( 8 7 ) r e p o r t e d a r e d u c t i o n i n
d i g e s t i b i l i t y o f c o r n s i l a g e -b a s e d d i e t s s u p p l e -
m e n t e d w i t h e i t h e r c o rn o r b a r l e y gr a in s
f o r l a c t a t i n g c o w s . T h e M E v a l u e o f t h e b a r l e y
d i e t w a s n o t i n f l u e n c e d b y i n t a k e w h e r e a s M E
v a l u e o f c o r n d i e t d e c r e a s e d a t h i g h e r i n ta k e s .
T h e d e c l i n e i n d i g e s t i b i l i t y w a s s im i l a r f o r t h e
t w o d i e t s . T h e d e c l i n e in d i g e s t i b i l i t y o f c e l l u l o s e
a n d h e m i c e l l u l o s e f ra c t i o n s w a s a b o u t 8 p e r -
c e n t a g e u n i t s a n d t h a t o f s t a r c h a b o u t 3 p e r-
c e n t a ge u n i t s p e r u n i t o f m a i n t e n a n c e i n c re a s e
i n i n t a k e .
W h e e l e r a n d N o l l e r (1 1 0 ) r e p o r t e d t h a t a
p a r t o f t h e r e d u c e d d i g e s t i b i l i t y o f e n e r g y in
l a c t a t i n g c o w s c o n s u m i n g c o r n g r a i n a n d
c o r n s i l a g e i n l a r g e a m o u n t s w a s p r e v e n t e d b y
s u p p l e m e n t a t i o n o f th e d i e t w i t h 2 .7 % l im e -
s t o ne . S u p p l e m e n t a t i o n w i t h l im e s t o n e in -
c r e a s e d f e c a l p H , r e d u c e d s t a r c h l o s se s in t h e
f e ce s , a n d i m p r o v e d f e e d e f f i c i e n c y . T h e y
s u g g e s t e d t h a t t h e i n c r e a s e d f e c a l p H r e f l e c t e d a
m o r e f a v o r a b l e in t e s t in a l p H f o r a c t i v i t y o f
p a n c r e a t i c a l p h a a m y l a s e .
P o o s e t a l . (7 5 ) s u p p l e m e n t e d d i e t s o f
l a c t a t i n g c o w s w i t h e i t h e r u r e a o r s o y b e a n o i l
m e a l ( S B O M ) . U r e a w a s e f f e c t i v e i n i m p r o v i n g
d i g e s t i b i l i t y o f d i e t s c o n t a i n i n g 1 1 .6 t o 1 3 .6 %
c r u d e p r o t e i n w h e n a d d e d i n a m o u n t s t o
i n c r e a s e c r u d e p r o t e i n t o 1 3 t o 1 4 . 2 % , b u t
o n l y S B O M w a s e f f e c t i v e a t h i g h e r p e r c e n t s .
T h e s e r e s u l t s s u g g e s t t h a t u r e a i s e f f e c t i v e in
i m p r o v i n g d i g e s t i b i l i t y a t h i g h e r c r u d e p r o -
t e i n i n l a c t a t i n g c o w s t h a n h a d b e e n s h o w n
p r e v i o u s l y f o r n o n p r o d u c i n g a n i m a l s . I m p r o v e d
d i g e s t i o n o f c o r n s i la g e d i e t s b y l a c t a t i n g
c o w s w i t h s u p p l e m e n t a l u r e a a ls o h a s b e e n
s h o w n b y V e r i t e ( 1 0 1 ) .
I n e x p e r i m e n t s w i t h l a c t a t i n g c o w s , T y r r e l l
a n d M o e ( 8 8 ) f o u n d a g r e a t e r e f f e c t o f i n t a k e
o n M E v a l u e a t l o w e r p r o t e i n t h a n a t h i g h e r .
W h e n d i e t s o f a l f a l fa h a y , c o r n , a n d S B O M w e r e
i n c r e a s e d f r o m 1 4 t o 1 7 % c r u d e p r o t e i n b y
s u b s t i t u t i o n o f co r n w i t h S B O M , b o t h D E a n d
M E w e r e i n c r e a s e d a t h i g h i n t a k e s . W h e n
p r o t e i n w a s i n c r e a s e d t o 2 0 % , h o w e v e r , o n l y
D E w a s i n c r e a s e d . W i t h c o r n s i l a g e d i e t s , D E
a n d M E w e r e i n c r e a s e d w h e n c r u d e p r o t e i n w a s
i n c r e a s e d f r o m 1 1 t o 1 4% b u t n o t w h e n c r u d e
p r o t e i n w a s i n c re a s e d f u r t h e r t o 1 7% . A d d i t i o n
o f 2 . 5 % l i m e s t o n e h a d n o e f f e c t o n d i g e s t i b i l i t y
o f e n e r g y in t h e l a t t e r e x p e r i m e n t .
Associa t ive L f fects L a c t a t i n g c o w s u s u a l l y
a r e f e d m i x e d d i e t s r a t h e r t h a n e i t h e r a ll f o r a g e
o r a l l c o n c e n t r a t e . T h e d i g e s ti o n o f m i x e d d i e t s
a t h ig h i n t a k e s c o m m o n l y i s c o m p a r e d w i th
d i g e s t i o n o f t h e s a m e d i e t a t a m a i n t e n a n c e
i n t a k e t o m e a s u r e i n t a k e e f f e c ts . A s s o c i a t i v e
e f f e c t r e f e r s t o d i g e s t i b i l i t y o f a m i x e d d i e t
d i f f e r e n t f ro m t h a t p r e d i c t e d f r o m d i r e c t
m e a s u r e m e n t o f t h e fo r a g e a n d c o n c e n t r a t e
s e p a r a t e l y . I n t a k e e f f e c t s a n d a s s o c i a t iv e e f f e c t s
a r e b a s i c a l l y t h e s a m e t h i n g , t h e i n c o m p l e t e
d i g e s t i o n o f a m i x e d d i e t a t a h i g h i n t a k e . T h i s
i s i m p l i c i t i n t h e e s t a b l i s h e d r e l a t i o n s h i p
b e t w e e n p e r c e n t a g e o f c o n c e n t r a t e a n d i n t a k e
e f f e c t s. T h e i m p o r t a n c e o f a s s o c i a t i v e e f f e c t s
f o r l a c t a ti n g c o w s c o n c e r n s a d d i t i v i t y o f t h e
d i g e s t i b il i t y o f c o m p o n e n t f e e d s i n a m i x e d
r a t i o n . I n f e e d e v a l u a t i o n s t u d i e s , t h e d i g e s t -
i b i l it y o f c o n c e n t r a t e s t y p i c a l l y is m e a s u r e d b y
d i f f e re n c e w i t h n o n p r o d u c i n g a n i m a l s, u s u a l ly
a t a m a i n t e n a n c e i n t a k e . B l a x t e r ( 2 0 ) s u m -
m a r i z e d e x t e n s i v e s t u d i e s o f M E o f d i e ts
c o n t a i n i n g 0 t o 6 0 % c o n c e n t r a t e w i t h s h e e p a t
m a i n t e n a n c e a n d c o n c l u d e d t h a t a s s o ci a t e d
e f f e c t s w e r e n o t a p r a c t i c a l p r o b l e m . A t h i g h e r
f e e d i n t a k e s , h o w e v e r , a s s o c i a t iv e e f f e c t s
c a n b e r e a l. A n e x a m p l e i s d e s c r i b e d b y J o a n n i n g
e t a l. ( 4 3 ) , w h o f o u n d d i g e s t i b i l i t y o f a m i x t u r e
o f c o r n g r a i n a n d c o r n s i la g e w a s 1 1% l es s t h a n
t h a t p r e d i c t e d f r o m d i g e s t i b il i t y o f t h e c o m -
p o n e n t f e e d s m e a s u r e d a t h i gh i nt a k e s. I n t a k e
e f f e ct s o n d i g e s t i b i l it y w e r e o b s e r v e d on m i x e d
d i e t s , b u t n o t w h e n e i t h e r c o r n s i la g e o r c o r n
g r a i n w a s f e d a l o n e . T h e s e d a t a a r e i l lu s t r a t e d i n
F i g u r e 1 .
I n t a k e e f f e c t s h a v e b e e n e x p r e s s e d b y V a n
S o e s t a n d c o w o r k e r s ( 1 0 0 ) b y d e s cr i b in g
d i s c o u n t f a c t o r s , w h i c h r e p r e s e n t t h e re -
d u c t i o n i n d i g e s t i b i l i t y o f s in g l e f e e d s t u f f s
w h e n i n t a k e i s i n c r e a s e d b y a n a m o u n t e q u a l t o
m a i n t e n a n c e . T h e y l i s t e d d i s c o u n t s f o r a l a r g e
n u m b e r o f f e e d s f r o m i n v iv o d a t a a n d i n v i t r o
d i g e s t i o n r a t e s a n d a v a i l a b le p a s s a g e ra t e s . T h e y
c o n c l u d e d t h a t f e e d s o f h i g h e r ce l l w a l l c o n t e n t
a n d o f a l o w d e g r e e o f l i g n i f i c a t i o n t e n d t o h a v e
t h e l a r g e s t d i s c o u n t s . T h e y a l s o s t a t e d t h a t
s t a r c h a d d s t o t h e c e l l w a l l e f f e c t i n c e r e a l
g r a in s . T h e u s e o f d i s c o u n t f a c t o r s f o r i n d i v i d u a l
f e e d s i n c o m p u t i n g t h e a c t u a l d i g e s t ib i l i ty o f
m i x e d d i e ts i n c o r p o r a t e s t h e s u s c e p t i b i l i t y o f
c o m p o n e n t f e e ds t o i n t a k e e f f ec t s . D i s c o u n t
f a c t o r s p r e s e n t e d b y V a n S o e s t e t a l . ( 1 0 0 ) ,
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2 6 M O E
R E L A T I O N S H I P B E T W E E N I N T A K E
E F F E C T A N D A S S O C I A T I V E E F F E C T
85
DRY
M A T T E R
DIGESTIBILITY
65 ;
M I N T E N N C E
NT E A N K A ~~
~ ~I-~/INTAKE1 IW/
,~. EFFECTL~~
/ ASSOCIATIVE
D LJBITUM EFFECT
I N T K E
100 ~ CORN SI LAG E~ 0
O ~ CORN GRAIN ~ 100
Figure 1. Data of Joanning et al. 43) show an
associative effect between corn grain and corn silage
at ad libitum intake but not at lower intake.
however, do not solve the proble m of non-
additivity or associative effects. A useful
extension of the discount concept will be a
procedure for estimating discounts for total
mixed rations so that the interactions between
fiber degradation and use of soluble carbo-
hydrates can be incorporated.
required to produce that product as in Figure 2.
With several physiological processes occurring
simultaneous/y, however, estimates of partial
efficiency for each process are clouded by
experimental error and also by necessary
assumptions. The most troublesome assumption
concerns maintenance. Three alternatives for
estima ting ener getic e ffic iency are in Figure 3.
The estimate may be derived from two or more
EB measurements made above maintenance in
which case the es timat e is by differe nce or
regression. The precision of the estimate is
determined by experimental error and by the
magnitude of the difference in energy intake
and pro duction. Alternativ e metho ds involve an
assumed amou nt of either ME or net energy
NE) required for mainte nance comb ined with
a single estimate of EB at some point above
maintenance. These alternative methods yield
lower errors because no error is associated with
the maintenance estimate. An incorrect as-
sumption regarding maintenance, however, will
introduce a bias. Considerable variation in
published estimates of partial efficienc y is from
differences in assumptions regarding main-
tenance.
P a r t i a l E f f i c i e n c y E s t i m a t i o n
Efficiency is the ratio between energy in the
product formed and the amount of energy
E N E R G Y
B A L A N C E
~ AEB
A M E
M E I N T A K E
E N E R G Y D I R E C T M E A S U R E
BALANCEoI / OFEFFICIENCY
E N E R G Y
B A L A N C
. . . .
M E I N T A K E
~ A S S U M E M E R EQ U IR EM E NT
F O R M A IN T E N A N C E
M E I N T A K E
META BOLIC EFFICIENCY - 3EB
A M E - k
A M I L K
k ; - A M E
k
-- A
GAI N
g A M E
Figure 2. Partial efficiency of metabolizable
energy ME) for production.
. . . . . . A S S U M E N E R E Q U IR E M E N T
F O R M A I N T E N A N C E
M E I N T A K E
Figure 3. Partial efficiency may be estimated by
regression top) or by assumed metabolizable energy
ME) or, net energy NE) required for maintenance.
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METABO LISM - - 75TH ANNIVERSARY ISSUE 11 27
T h e p r o b l e m s a s s o c i a t e d w i t h m a t h e m a t i c a l
e s t i m a t e s o f p a r t i a l e f f i c i e n c y , i n c l u d i n g t h e
c o n c e p t s o f m a i n t e n a n c e , w e r e d i s c u s s e d
e x t e n s i v e l y b y V a n E s (9 5 ) . H e e m p h a s i z e d
l i m i t a t i o n s o f t h e c o n c e p t o f n e t e n e r g y f o r
m a i n t e n a n c e a n d e f f i c ie n c y o f e n e rg y u s e
f o r m a i n t e n a n c e . E n e r g y r e q u i r e d f o r m a i n -
t e n a n c e is p r i m a r i l y f o r t h e p r o d u c t i o n o f A T P ,
a n d t h i s e n e r g y a l o n g w i t h t h e w a s t e d e n e r g y i s
l o s t e v e n t u a l l y a s h e a t. H e a t p r o d u c t i o n a t
m a i n t e n a n c e i s, t h e r e f o r e , t h e t o t a l o f p r o -
d u c t i v e a n d n o n p r o d u c t i v e e n e r g y . H e a t p r o -
d u c e d b y t h e f a s t i n g a n i m a l i s t h e r e s u l t o f
b o d y t i s s u e b e i n g m e t a b o l i z e d t o s u p p l y t h e
e n e r g y n e e d e d t o m a i n t a i n t h e a n i m a l . T h e
r a t i o b e t w e e n f a s t in g a n d m a i n t e n a n c e h e a t
p r o d u c t i o n i s, t h e r e f o r e , a n e x p r e s s i o n o f t h e
r e l a t i v e e f f i c i e n c y o f b o d y t i ss u e e n e r g y a n d
d i e t a r y e n e r g y i n m e e t i n g t h e n e e d s f o r m a i n -
t e n a n c e . E f f i c i e n c ie s c a l c u l a t e d i n s u c h a
m a n n e r s h o u l d b e r e f e rr e d t o a s a p p a r e n t
e f f i c i e n c y a n d b e a r l it t l e r e l a t i o n s h i p t o t h e
e f f i c i e n c y c o m p u t e d f o r e n e r g y u s e a b o v e
m a i n t e n a n c e i n w h ic h a m e a s u r e a b l e e nd
p r o d u c t i s fo r m e d .
V a n E s ( 9 5 ) a l s o d i s c u s s e d e r r o r s a s s o c i a t e d
w i t h e s t i m a t i o n o f m a i n t e n a n c e r e q u i r e m e n t b y
r e g r es s i o n . H e n o t e d t h a t r e g r e s s i o n a n a l y s e s
t h e o r e t i c a l l y r e q u i re t h a t t h e i n d e p e n d e n t
v a r i a b l e( s ) b e m e a s u r e d w i t h o u t e r r o r . I f n o t ,
t h e c o m p u t e d r e g r es s i o n c o e f f i c i e n t s w il l b e
u n d e r e s t i m a t e d . S i n ce M E a n d E B b o t h a r e
m e a s u r e d w i t h e r r o r , i n c l u d i n g s o m e s o u r c e s o f
e r r o r s u c h a s f e c a l, m e t h a n e , a n d u r i n e l o s s e s
t h a t a r e c o m m o n t o b o t h , t h e m o d e l s e le c t e d
w i l l i n f l u e n c e e s t i m a t e s o f p a r t i a l e f f ic i e n c y a n d
t h e e s t i m a t e o f m a i n t e n a n c e .
C r a m e r ( 2 8 ) d e s c r i b e d a n o r t h o g o n a l r e -
g r e ss i on p r o c e d u r e t h a t a c c o m m o d a t e s e r r o r s in
b o t h v a r i ab l e s . I t m i n i m i z e s t h e p e r p e n d i c u l a r
d i s t a n c e s f r o m t h e l i n e t o t h e p o i n t s r a t h e r t h a n
t h e v e r t i c a l d i s t a n c e s f r o m t h e l i n e t o t h e p o i n t s
a s i n c o n v e n t i o n a l r e g r e s s i o n .
B e c a us e o f t h e s o u r ce s o f e r r o r c o m m o n t o
E B a n d M E , a s y s t e m h a s b e e n p r o p o s e d i n
w h i c h r e t a i n e d e n e r g y ( R ) i s r e l a t e d t o gr o s s
e n e r g y i n t a k e ( G ) b y s c a li n g b o t h w i t h f a s t in g
h e a t p r o d u c t i o n i n a g e n e r a li z e d f o r m o f th e
M i t sc h er li ch e q ua t io n R = B ( 1 - e x p ( p G ) ) - l ,
w h e r e t h e p a r a m e t e r s B a n d p a r e f i t t e d b y a n
i t e r a t i v e p r o c e d u r e ( 1 9 , 2 1, 2 2 ) . T h i s t e c h n i q u e
a v o i d s a s s u m p t i o n s r e g a r d i n g m a i n t e n a n c e
r e q u i r e m e n t s b u t r e q u i re s d i re c t m e a s u r e m e n t
o f f a s t in g h e a t p r o d u c t i o n b y e a c h t e s t a n im a l
o r a t a b u l a t i o n o f f a s t i n g h e a t p r o d u c t i o n
a c c o r d i n g t o b r e e d , s i z e , s e x , a n d o t h e r a t t r i -
b u t e s a n d o f th e e n e r g y r e t e n t i o n s a s s o c ia t e d
w i t h g a i n s i n b o d y w e i g h t ,
W i t h t h e i n c r e a s e d a t t e n t i o n t o th e d e s -
c r i p t i o n o f t h e m a i n t e n a n c e c o m p o n e n t i n
g r o w i n g a n i m a ls , W e b s t e r e t al . ( 1 0 6 ) c o m p u t e d
a b a s a l c o m p o n e n t o f m e t a b o l i s m r e l a te d t o
l iv e w e i g ht f r o m E B m e a s u r e m e n t w i t h g r o w i n g
s t ee r s an d c o n c l u d e d t h a t t h e b a s a l c o m p o n e n t
w a s c l o s e l y re l a t e d t o b o d y w e i g h t t o th e
e x p o n e n t . 7 3 4 . T h i s e s t i m a t e w a s , h o w e v e r ,
o b t a i n e d b y c a l c u la t i n g t h e b a s a l c o m p o n e n t
f r o m a s s u m e d r e l a t i o n s h i p s b e t w e e n Q (% M E
i n t h e d i e t ) a n d k m a n d k f ( 1 ) w h i c h i n v o l v e
m a i n t e n a n c e o f m a t u r e a n i m a ls a n d e f f i c ie n c y
o f f a t t en i n g . B e c a u se a c tu a l m e a s u r e m e n t o f
f a s t in g m e t a b o l i s m i n t h e s e a n i m a l s d e c l i n e d
w i t h i n c r e a s i n g w e i g h t w h e n e x p r e s s e d a s
k c a l / k g 73 in a c c o r d w i t h A R C ( 1 ) , t h e a u t h o r s
c o n c l u d e d t h a t t h e s e f i n d i n g s c a s t s e r i o u s d o u b t
o n t h e v a l i d i t y o f u s e o f m e a s u r e d f a s ti n g
m e t a b o l i s m a s a b a s e l i n e f r o m w h i c h t o p r e d i c t
e f f i c i e n c y o f g r o w t h .
T h e u n c e r t a i n t i e s a s s o c i a t e d w i t h s t a t i s t i c a l
p a r t i t i o n i n g o f e n e r g y c o s t i n t h e p r o d u c i n g
a n i m a l in t o m a i n t e n a n c e a n d p r o d u c t i o n
a re c o n s i d e r a b l e . A l t h o u g h n e w e r m a t h e m a t i c a l
t e c h n iq u e s e v e n t u a ll y m a y p e r m i t a b a n d o n m e n t
o f t h e c o n c e p t o f m a i n t e n a n c e , e s p e c i a ll y i n t h e
g r o w i n g a n i m a l , i t i s a u s e f u l a n d n e c e s s a r y
c o m p o n e n t i n d i s c u s s in g e n e r g y u s e b y a n i m a l s
o f d i f f e r i n g p r o d u c t i o n r a t e s . I n t h e d i s c u s s i o n s
t h a t f o l l o w , t h e r e a d e r i s r e m i n d e d t h a t a s-
s u m p t i o n s r e g a rd i n g m a i n t e n a n c e e x e r t c o n -
s i d e ra b l e e f fe c t o n e s t i m a t e s o f p r o d u c t i o n
e f f i c i e n c y .
M a i n t e n a n c e a n d a c t a t io n
C a l o r i m e t r i c e x p e r i m e n t s b y B r o u w e r e t a l .
( 2 5 ) a n d V a n E s (9 4 ) s h o w e d t h a t t h e v a l u e o f
a s e r i e s o f h a y s f o r m a i n t e n a n c e o f c o w s w a s
m o r e c l o s e ly r e la t e d t o t h e i r M E c o n t e n t t h a n
t o s t a r c h e q u i v a l e n t . B l a x t e r ( 1 6 ) s u m m a r i z e d
r e s u l ts o f c a l o r i m e t r i c s t u d i e s w i t h d i e t s r a n g i n g
f r o m p o o r q u a l i t y f o r a g e t o al l c o n c e n t r a t e a n d
c o n c l u d e d t h a t e f f i c ie n c y o f u s e o f M E f o r
m a i n t e n a n c e w a s f a i r l y c o n s t a n t . T h e s e r e s u lt s
s u p p o r t e d t h e c o n c lu s i o n o f R i t z m a n a n d
B e n e d i c t ( 8 0 ) f r o m e a r l i e r c a l o r i m e t r i c s tu d i e s .
B l a x t e r ( 1 6 ) c o n c l u d e d f u r t h e r t h a t t h e e l -
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ficiency for maintenance of ME from these
natural feeds was equal to that of VFA infused
into the rumen when a correction was made for
the heat of fermentation of the natural feeds.
These studies showed that the variation in
use of ME for mai ntenan ce was low, but some
variation did exist, presumably in part from
losses in heat of fermentation, which was not
measured in the determination of ME. Agri-
cultural Research Council (1) described variation
in efficiency of use of energy for maintenance
(k m) as a funct ion of percentage of ME in the
diet (Qm) as follows: k m 54.6 + .30 Qm-
A major question, unresolved in earlier
calorimetric investigations, was the extent to
which efficiency of ME for milk production
was influenced by the source of dietary ME.
Initial lactation studies at Beltsville (27) were
with diets of alfalfa hay and concentrates
in ratios calculated to provide 50, 75, and 100%
of estimated net energy (ENE) from the alfalfa.
When maintenance was assumed to be 131 kcal
ME/kg -Ts , efficienc ies of use o f ME in excess of
mai nten ance were 65, 61, and 54%, respectively,
for lactation.
Hashizume et al. (42) found the efficiency
of ME of diets con tai ning 45 and 71% of
concentrate consumed in excess of maint enance
(116.3 kcal/kg vs ) was used with efficiencies of
74.0 and 68.2%, respectively, for milk plus
retained body tissue energy.
Van Es and Nijkamp (98) reported the
results of 41 balance trials with lactating cows
consuming mixed diets of concentrate, silage,
and variable amounts of hay. In these studies,
no effects of percentage of crude fiber or of
crude protein on efficiency of milk product ion
were detected. Also, no differences in util izat ion
of hay and silage of equal ME and protein
content were found. These workers concluded
that ME was used for milk production with an
efficiency (kl) of 54 to 58% and that 10.1 to
11.7 Mcal ME was required for the maintenance
of a 500 kg cow (96 to 111 kcal ME/kg'VS).
Van Es and Nijkamp (98) discussed problems
associated with mathe matical descriptions of
results of experiments with lactating cows in
positive or negative body tissue EB. Relation-
ships between ME intake and milk energy were
studied by multiple regression with separate
terms for body weight, milk energy, tissue
energy gain, and tissue energy loss and by
applying several methods of adjusting to zero
body tissue EB. The various methods yielded
slightly different estimates of efficiency but all
method s indicated a slight increase in efficiency
of ME use for milk production with an increase
in metabolizability of the diet.
An extensive series of EB experiments by
Flatt et al. (37) with Holstein cows producing
up to 49 kg of 4% fat-corrected milk (FCM) per
day and con suming diets of 40, 60, and 80%
concentrate plus alfalfa hay showed no signifi-
cant differences among diets in effi ciency of
use of ME for milk production plus tissue
energy gain. These studies included cows at all
stages of lactation and when non lact atin g and
at both ad libitum and restricted feeding. The
magnitude of changes in body tissue energy
status was far greater than in previous experi-
ments and varied from -20.6 to +18.3 Mcal
body tissue energy per day. Differences due to
diet were in body tissue ba lance; cows on the
highest concentrate diet mobilized less fat in
early lactation and deposited more fat in late
lactation than cows on the highest forage diets
at equal ME intake. The regression of total EB
of milk plus body tissue energy on ME intake
was EB (kcal/kg 7s) = - 93.4 + .66 i .011 ME
(kcal/kg'VS). This equation indicated 66%
utilization of ME and zero EB at 142 kcal
ME/kg vs. Extensive mathematical analyses of
these data led to several conclusions: 1) use of
ME for milk or body tissue gain was relatively
unaffected by milk yield, amount of body
tissue gain (or loss), and stage of lactation; 2)
the major difference among diets as well as
among individual cows was in the amount
consumed and energy partition, i.e., milk
production or fattening, rather than the ef-
ficiency with which ME was used; and 3) the
apparently high maintenance requirement was
not due to milk yield or to lactation per se but
may have been influenced by pregnancy.
The ad libitum feeding of high protein
(19.5%) diets in the experiment of Flatt et al.
(37), although necessary to meet the objectives
of that experiment, provided substantially more
protein than needed for maintenance plus milk
production. The effects of excess protein as
well as the contribution of pregnancy were
studied with all available data from Behsville,
which included 350 trials with lactating cows
and 193 with n onlacta ting cows. The decrease
in EB attributable to intake of nitrogen in
excess of protein required was 7.3 kcal/g excess
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ME T ABOL I SM - - 7 5 TH ANNI VE RSARY I SSUE 1 1 2 9
n i t r o g e n ( 9 0 ). T h e a m o u n t o f M E r e q u i r e d
d u r i n g p r e g n a n c y w a s d e s c r i b e d (5 7 ) b y t h e
e q u a t i o n M E ( k c a l / k g 7 s) = 1 0 0 . 8 + . 5 6 7 e 174t
o n d a y t o f g e s t a t i o n . T h e s e d a t a in d i c a t e
1 1 .5 % e f f i c i e n c y o f M E f o r f e t a l g a in .
M u l t i p l e r e g r e s s i o n a n a l y s i s w e r e u s e d b y
M o e e t a l. (6 2 , 6 3 ) t o d e r i v e e s t i m a t e s o f
m a i n t e n a n c e n e e d s a n d p a r t i a l e f f i c i e n c i e s
o f m i l k p r o d u c t i o n a n d t i s s u e g a i n i n T a b l e s 3
a n d 4 . P a r t i a l e f f i c i e n c i e s o f M E u s e d f o r m i l k
p r o d u c t i o n a n d b o d y g a in i n l a c t a t in g c o w s
w e r e 6 4 a n d 7 5 % a n d e f f i c i e n c y o f m a t e r n a l
b o d y g a i n in n o n l a c t a t i n g c o w s w a s 6 0 % . T h e
e f f i c i e n c y o f u s e o f b o d y t i s s u e e n e r g y f o r m i l k
p r o d u c t i o n b y c o w s i n e a rl y l a c t a ti o n w a s
e s t i m a t e d b y c o m p a r i n g p a r t ia l re g r e ss i o n
c o e f f ic i e n t s r e p r e s e n t i n g t h e a m o u n t o f M E
r e q u i r e d fo r m i l k p r o d u c t i o n a n d t h e a m o u n t
o f d i e t a r y M E s p a r e d b y b o d y t i s s u e l o s s. T h e
e s t i m a t e d c o n v e r s io n o f b o d y t is s u e e n e r g y to
m i l k e n e r g y w a s 8 2 % e f f i c i e n t a n d ~ i k e l y
r e fl e c ts s u b s t a n t ia l d i r e c t i n c o r p o r a t i o n o f b o d y
l i p i d s i n t o m i l k f a t . T h e s e r e s u l t s s h o w e d t h a t
t e m p o r a r y s t o r ag e o f e n e r g y a s b o d y f a t i n l a t e
l a c t a t i o n c o m b i n e d w i t h u s e o f b o d y f a t i n
e a r l y l a c t a t i o n i s n e a r l y a s e f f i c i e n t a s d i r e c t u s e
o f d i e t a r y M E f o r m i l k p r o d u c t i o n
(75
X 8 2 %
= 6 2 % v s . 6 4 %) .
T h e f i n d i n g s d e s c r i b e d in th e p r e c e e d i n g
p a r a g r a p h w e r e u s e d b y M o e e t a I. ( 5 5 ) t o
i d e n t i f y t h e r e l a t io n s h i p b e t w e e n d i e t q u a l it y
a n d e f f i c i e n c y o f m i l k p r o d u c t i o n . E n e r g y o f
d i e t s w a s e x p r e s s e d a s n e t e n e r g y f o r l a c t a t i o n
(N E 1). M a i n t e n a n c e r e q u i r e m e n t s e s t i m a t e d b y
p o o l e d l i n e a r r e g r e s s i o n w i t h i n 3 2 d i e t s f r o m
t h e 3 5 0 t r i a l s w i t h l a c t a t i n g c o w s w e r e 1 2 2 .1
a n d 1 1 1 . 3 k c a l M E o r 7 8 . 9 a n d 6 7 . 7 k c a l N E 1
p e r k g 7s o f b o d y w e i g ht , d e p e n d i n g o n w h e t h e r
M E i n t a k e o r m i l k e n e rg y w a s t h e d e p e n d e n t
v a r i a b l e . B e c a u s e t h e a v e r a g e m e a s u r e d f a s t i n g
h e a t p r o d u c t i o n i n th e B e l t sv i ll e l a b o r a t o r y
( 7 3 . 5 k c a l/ k g 'V S ) w i t h n o n l a c t a t i n g , n o n -
p r e g n a n t d a i r y c o w s f o l l o w i n g a p e r i o d o f
m a i n t e n a n c e f e e d in g (3 5 ) w a s b e t w e e n t h e
r e g r e s s io n e s t i m a t e s ( 7 8 . 9 a n d 6 7 . 7 ) o f t h e NE 1
r e q u i re d f o r m a i n t e n a n c e , t h e a u t h o r s c o n c l u d e d
t h a t t h e a m o u n t o f e n e rg y r e q u i r e d f o r m a i n -
t e n a n c e o f l a c t a t i n g c o w s c o u l d b e d e s c r i b ed
a d e q u a t e l y a s 7 3 k c a l NE 1 ( o r N E m i l k ) / k g Ts
a n d t h a t a s e p a r a t e N E t e r m f o r m a i n t e n a n c e
( N E m ) w a s u n n e c e s s a r y .
W i t h t h a t a s s u m p t i o n , t h e N E 1 o f i n d i v i d u a l
d i e t s w a s s t u d i e d b y r e l a t i n g N E 1 o f d i e t d r y
m a t t e r ( D M ) t o o t h e r e x p r e s s i o n s o f e n e r g y a s
f o l l o w ( r e g r e ss i o n c o e f f i c i e n t -+ S E ) :
N E I ( M c a l / k g D M ) = - - . 1 9 +
( . 7 03 + . 0 2 0 ) M E ( M c a l / k g D M ) ,
N E 1 ( M c a l / k g D M ) = - - . 3 6 +
( . 6 7 7 + .0 2 2 ) D E ( M c a l / k g D M ) , a n d
N E 1 ( M c a l / k g D M ) = - - . 1 2 +
( . 0 2 6 6 + .0 0 1 1 ) T D N ( % o f D M ) .
T h e M E , D E , a r id t o t a l d i g e s t i b l e n u t r i e n t s
( T D N ) i n t h e s e e q u a t i o n s w e r e t h o s e a c t u a l l y
o b s e r v e d i n t h e l a c t a t i n g a n i m a l , a n d t h e
a u t h o r s e m p h a s i z e d t h a t t h o s e r e l a t i o n s h i p s
w e r e n o t a p p r o p r i a t e f o r m e a s u r e m e n t s o f
d i g e s t i b i l i t y a t m a i n t e n a n c e . T h e s e r e s u l t s
i n d i c a t e 6 1 t o 6 4 % e f f i c i e n c y o f M E u s e f o r
m i l k p r o d u c t i o n f r o m n o r m a l d i et s .
I n a r e c e n t a n a l y s i s o f B e l t s vi l le d a t a ( 6 1 ) ,
r e s u l t s o f 3 1 3 e n e r g y b a l a n c e t ri a l s w i t h l a c t a t i n g
c o w s p u b l i s h e d s i n c e 1 9 7 0 w e r e u s e d t o s t u d y
t h e s a m e r e l a t i o n s h i p s . T h e r e l a t i o n s h i p s
b e t w e e n N E1 a n d o t h e r e x p r e s s i o n s o f e n e r g y
f r o m t h i s s e p a r a t e d a t a s e t w e r e :
N E1 ( M c a l / k g D M ) = - . 2 1 +
( .6 97 -+-+ 02 2) M E (M ca l /k g DM ),
N E 1 ( M c a l / k g D M ) = - . 4 1 +
( . 6 7 3 -+ . 0 2 1 ) D E ( M c a l / k g D M ) , a n d
N E1 ( M c a l / k g D M ) = - . 5 1 +
( . 0 3 1 5 -+ . 0 0 1 5 ) T D N ( % o f D M ) .
T h e M E a n d D E e q u a t i o n s a r e v i r t u a l ly i d e n ti c a l
t o t h o s e d e r i v e d e a r li e r w i t h a t o t a l l y d i f f e r e n t
d a t a s e t . T h e c o e f f i c i e n t f o r t h e T D N e q u a t i o n
i s a b o u t 1 8% g r e a t e r t h a n i n t h e e a r l i e r e q u a t i o n ,
i n d i c a t i n g a g r e a t e r e f f e c t o f p e r c e n t T D N o n
N E 1 t h a n i n t h e e a r l i e r d a t a s e t. T h e c h a n g e i n
t h e T D N e q u a t i o n i s u n e x p l a i n e d a l t h o u g h t h e
m o r e r e c e n t d a t a s e t i n c l u d e d s e v e r a l d i e t s
c o n t a i n i n g s i la g e f o r w h i c h d r y i n g l o s s e s a n d
e t h e r e x t r a c t a n a l y se s m a y h a v e i n t r o d u c e d
e r r o r s n o t i n M E a n d D E d a t a . G r e a t e s t r e l i a n c e
s h o u l d b e p l a c e d o n M E a n d D E e q u a t io n s
b e c a u s e t h e y a r e b a s e d o n d i r e c t c o m b u s t i o n o f
w e t m a t e r ia l . F o r p r a c t i ca l u s e t h e M E e q u a t i o n s
g i v en a b o v e c a n b e s i m p l i f e d t o N E I (M c a l / k g
D M ) = - - . 2 + . 7 M E ( M c a l / k g D M ) i n w h i c h M E
h a s b e e n a d j u s t e d f o r i n t a k e a n d a s s o c i a t e d
e f f e c t s .
M a i n t e n a n c e a n d r o w t h
M e a s u r e m e n t o f e n er g y c o s t o f g r o w t h i n
Journa l of Dairy Science Vol. 64, N o. 6 , 1981
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1 1 3 0 M O E
T A B L E 3 . M u l t i p l e r e gr e s si o n a n a l y s is o f m e t a b o l i z a b l e e n e r g y ( M E ) i n t a k e ( M c al M E / d a y ) d u r i n g 5 4 3 e n e r g y
b a l a n c e m e a s u r e m e n t s w i t h d a i r y c o w s a ,
M e t a b o l i c B o d y t i s su e B o d y t i ss u e
b o d y s i ze M i l k e n e r g y g a i n l o s s
( k g 75 ) ( M c a l ) ( M c a l ) ( M c a l ) C o n s t a n t
L a c t . , n e g . b a l a n c e ( N = 1 2 6 , R ~
=.957,
S y . x = 1 . 8 8 6 , M E = 3 0 . 0 6 0 ,+ 9 . 0 M c aI )
C o e f f i c i e n t . 1 5 3 ,+ . O 1 2 1 . 5 1 2 -+ . 0 3 4
A v e r ag e 1 1 4 . 6 1 4 . 8 8 2
L a c t . , p o s . b a l a n c e ( N = 2 2 4 , R u = . 9 5 0 , S y . x = 2 . 0 2 5 , M E = 3 2 . 7 2 6 +- 9 . 0 M c a l )
C o e f f i c i e n t . 1 3 5 ,+ . 0 0 9 1 . 5 7 6 + . 0 2 9 1 . 3 7 8 ,+ . 0 5 4
A v e r a g e 1 1 3 . 0 9 . 4 1 6 3 . 2 8 8
D r y c o w s , n e g . b a l a n c e ( N = 7 5 , R 2 - . 7 0 7 , S y . x = l . 7 3 5 , M E = I O . 4 0 1 ,+ 3 .1 M c a l )
C o e f f i c i e n t . 0 5 0 -+ . 0 1 5
A v e r a g e 1 2 9 . 9
D r y c o w s , p o s . b a l a n c e ( N = 1 1 8 , R 2 = . 8 9 7 , S y . x = l . 5 0 3 , M E = 1 8 . 1 4 0 ,+ 4 . 6 M c a l )
C o e f f i c m n t . 0 8 9 ,+ . 0 1 1 1 . 7 0 3 -+ . 0 5 8
A v e r a g e 1 2 8 . 1 3 . 1 6 0
L a c t a t i n g c o w s ( N = 3 5 0 , R 2 = . 9 5 2 , S y . x = l . 9 8 5 , M E = 3 1 . 7 6 6 + 9 . 0 M c a l )
C o e f f i c i e n t . 1 4 1 +- . 0 0 7 1 . 5 5 2 ,+ . 2 2 1 . 3 3 9 ,+ . 0 4 5
A v e r a g e 1 1 3 . 6 1 1 . 3 6 6 2 . 1 0 1
D r y c o w s ( N = 1 9 3 , R 2 = . 9 1 1 , S y . x = l . 6 7 6 , M E = 1 5 . 1 3 3 ,+ 5 .6 M c al )
C o e f f i c i e n t . 0 7 2 ,+ . 0 0 9 1 . 6 7 7 -+ . 0 5 5
A v e r a g e 1 2 8 . 8 1 . 9 3 2
A l l c o w s ( N = 5 4 3 , R 2 = . 9 6 8 , S y . x = 2 _ 0 7 5 , M E = 2 5 . 7 4 0 ,+ 1 1 . 5 M c a l)
C o e f f i c i e n t . 1 0 4 . 0 0 6 1 . 6 2 3 ,+ . 0 1 4 1 . 4 7 3 ,+ . 0 3 6
A v e r a g e 1 1 9 . 8 7 . 3 9 8 2 . 0 4 5
1 . 2 7 0 ,+ . 0 4 5 - - 2 . 8 8 9
- - 5 . 4 7 9
- - 1 . 8 8 9
. 9 9 0 -+ . 0 9 1 6 . 7 8 1
- - 2 . 9 0 4
1 4 0 1
1.279 . 0 3 4 - -2 .152
- - 1 . 9 7 2
. 9 3 3 -+ . 0 6 5 3 . 6 7 0
- 1 . 1 2 8
1 . 2 3 4 +- . 0 2 8 . 6 2 2
- 1 . 9 37
a D a t a f r o m M o e e t a l . ( 6 2 ) .
c a t t l e i s m a d e d i f f i c u l t b y t h e c o m b i n e d e f f e c t s
o f a p p a r e n t d e c l i n i n g m a i n t e n a n c e n e e d s as t h e
a n i m a l a p p r o a c h e s m a t u r i t y a n d t h e c h a n g e s i n
c o m p o s i t i o n o f t i s s u e d e p o s i t e d w i t h a g e a n d
l e v e l o f f e e d i n g . F a s t i n g h e a t p r o d u c t i o n o f
c a t t l e w h e n e x p r e s s e d p e r u n i t o f m e t a b o l i c s i z e
d e c l i n e s w i t h a g e a s i n T a b l e 5 . V a r i o u s e x -
p o n e n t s o f b o d y w e i g h t h a v e b e e n u s e d t o
d e s c r i b e m e t a b o l i c s i ze ( 4 7 ) . E v e n s m a l l d if f e r -
e n c e s i n e x p o n e n t p r o d u c e l a rg e d i f f e r e n c e s in
e s t i m a t e s a s c a n b e s e e n b y c o m p a r i n g f a s t i n g
h e a t p r o d u c t i o n e x p r e s s e d p e r u n i t w e i g h t
r a i s e d t o t h e e x p o n e n t s . 7 3 a n d . 7 5 i n T a b l e 5 .
A s o r t o f g e n t l e m a n ' s a g r e e m e n t t o e x p r e s s
r e s u l t s o f E B m e a s u r e m e n t s b y t h e e x p o n e n t
. 7 5 w a s r e a c h e d a t t h e th i r d S y m p o s i u m o n
E n e r g y M e t a b o l i s m . T h i s a g r e e m e n t w a s i n -
t e n d e d t o f a c i l i t a t e c o m p a r i s o n s o f r e s u l t s f r o m
T A B L E 4 . E s t i m a t e s o f m a i n t e n a n c e r e q u i r e m e n t a n d p a r t ia l e f f i c ie n c y o f e n e r g y u s e in t h e d a i r y c o w a .
M E b f o r M i l k T i s s u e M i l k
m a i n t e n a n c e f r o m M E f r om M E f r o m t is s ue
N (k ca l /k g Ts ) (%)
L a c t a t i n g c o w s 3 5 0 1 2 2 6 4 . 4 7 4 . 7 8 2 . 4
N o n l a c t a t i n g c o w s 1 9 3 1 0 0 5 9 . 6
a D a t a f r o m M o e e t a l . ( 6 2 ) .
b M E i s m e t a b o l i z a b l e e n e r g y .
J o u r n a l o f D a i r y S c i e n c e V o l . 6 4 , N o . 6 , 1 9 8 1
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METABO LISM - - 75TH ANNIVERSARY ISSUE 1 131
TABLE 5. Preferred fasting heat production of catt le .
Age of Body Fast ing metabo l ism
animal a weight b
(mo nths ) (kg) (kcal/kg.73 a)
(kcal/kg'~S c)
55 140 129
3 80 135 124
6 150 125 113
12 275 110 98
18 400 100 89
24 525 95 84
36 650 90 79
48 650 85 70
48 650 80 70
aFrom A RC (1) .
bsug gested mean bod y weights of growing large breed dairy ca tt le for correspon ding ages, f rom N RC (66).
CRecalculated from Columns 2 and 3.
d i f f e r e n t l a b o r a t o ri e s . T h e u s e o f b o d y w e i g h t
i n k g T s r e d u c e s v a r i a t io n f r o m m a t u r e b o d y
s i z e i n f a s t i n g h e a t p r o d u c t i o n a n d p r e s u m a b l y
m a i n t e n a n c e r e q u i r e m e n t . T h e u s e o f m e t a b o l i c
b o d y s iz e to p a r t i t i o n e n e r g y u s e b e t w e e n
m a i n t e n a n c e a n d p r o d u c t i o n i s a p p a r e n t l y l es s
s u i t a b l e f o r t h e y o u n g g r o w i n g a n i m a l t h a n f o r
a d u lt s . R e c e n t w o r k o n t h e p a r t i ti o n a n d
e n e r g y c o s t o f p r o t e i n a n d f a t g a in a n d w o r k o n
t h e e n e r g y c o s t o f p r o t e i n t u r n o v e r , h o w e v e r , is
h e l p i n g t o c l a r i f y e n e r g y t r a n s a c t i o n s i n y o u n g
g r o w i n g a n i m a l s .
S e v e r a l r e c e n t r e v i ew s d i s c u s s m a n i p u l a t i o n
o f g r o w t h ( 3 2 ) , e n e r g y c o s t o f g r o w t h ( 5 2 ) , a n d
n u t r i t i o n a n d g e n e t i c e f fe c t s o n b o d y c o m p o s i -
t i o n ( 5 0 ) .
T h o r b e k ( 8 3 ) c o m p u t e d e f f ic i e n c ie s f o r
b o d y g a i n i n g r o w i n g p i g s w i t h B r i e r e m ' s ( 2 4 )
e s t i m a t e o f m a i n t e n a n c e n e e d s , 1 9 6 . 3 k c a l M E
p e r k g -s 6 b o d y w e i g h t . D e c l i n e i n e f f i c i e n c y
o f M E f o r g a i n w a s l i n e a r w i t h i n c r e a s i n g
p e r c e n t a g e o f t o t a l g a i n a s p r o t e i n . U s i n g a
l i n ea r f u n c t i o n f o r m a i n t e n a n c e M E ( 1 6 83 +
8 . 1 L W f o r l i v e w e i g h t s ( L W ) b e t w e e n 2 0 a n d
9 0 k g) , T h o r b e k ( 8 4 ) f o u n d p a r t i a l e f f i c i e n c i e s
f o r p r o t e i n a n d f a t d e p o s i t i o n o f 4 3 a n d 7 7 .
K i e l a n o w s k i a n d K o t a r b i n s k a ( 4 6 ) s t u d i e d
s e v er a l e x p o n e n t s o f b o d y w e i g h t i n d e s c r ib i n g
r e l a ti o n s h i p s b e t w e e n M E i n t a k e o r h e a t
p r o d u c t i o n a n d p r o t e i n a n d f a t g a i n i n g r o w i n g
p ig s. T h e y f o u n d t h e e x p o n e n t . 7 3 4 f i t b e s t a n d
u s e d . 7 5 f o r s i m p l i c i t y . E n e r g y c o s t o f p r o t e i n
d e p o s i t i o n w a s 1 6 k c a l M E / g , a n d c o s t o f f a t
d e p o s i t i o n w a s 1 3 k c a l M E / g . T h o s e e s t i m a t e s
c o r r e s p o n d t o p a r t i a l e f f i c i e n c i e s o f a b o u t 3 5
a n d 7 1 , r e s p e c t i v e l y .
P a r t i a l e f f i c i e n c y o f p r o t e i n a n d f a t ga i n i n
g r o w i n g l a m b s ( 3 0 t o 6 0 k g ) w a s e s ti m a t e d
f r o m E B a n d f a s ti n g m e a s u r e m e n t s o f h e a t p r o -
d u c t i o n ( 1 0 ) . P a r t i a l e f f i c ie n c i e s w e r e 7 6 f o r
m a i n t e n a n c e , 35 f o r p r o t e i n g a i n , a n d 9 9 f o r
f a t g a in w h e n a w e i g h t e x p o n e n t o f . 7 5 w as
u s e d . R e c e n t w o r k w i t h c a lv e s ( 7 2 ) a n d w i t h
b u l l s a n d h e i f e r s ( 3 8 ) a l s o s h o w s a l o w e r
e n e r g e t i c e f f i c i e n c y f o r p r o t e i n g a i n t h a n f o r f a t
ga in .
M i l l w a r d e t a l . ( 5 2 ) e m p h a s i z e d t h a t s t a t i s -
t i c a l id e n t i f i c a t i o n o f h e a t p r o d u c t i o n a s s o c i a t e d
w i t h p r o t e i n a n d f a t d e p o s i t i o n , a l t h o u g h u s e f u l
t o p r e d i c t g r o w t h p e r f o r m a n c e i n a n im a l s , i s
a r g u a b l y m i s l e a d i n g i n m e c h a n i s t i c t e r m s .
P r o t e i n a n d f a t d e p o s i t i o n s a r e n o t c o m p l e t e l y
i n d e p e n d e n t e v e n t h o u g h f a t d e p o s i t i o n is
l i k e l y m o r e m a n i p u l a b l e t h a n p r o t e i n d e p o si -
t i o n . I f s o m e f a t i s d e p o s i t e d a s a n i n s e p a r a b l e
c o m p o n e n t o f l e a n ti s su e g r o w t h , t h e c o s t o f
t h a t f a t d e p o s i t i o n w i l l be s t a t i s t i c a l l y i d e n t i f i e d
w i t h p r o t e i n d e p o s i t i o n a n d t h e e f f ic i e n c y o f
p r o t e i n s y n t h e s i s t h e r e b y w i l l b e u n d e r -
e s t i m a t e d .
T h e c o n t r i b u t i o n o f p r o t e i n t u r n o v e r t o t h e
a p p a r e n t l y h i gh c o s t o f n e t p r o t e i n s y n t h e s is
a n d t h e h i g h e r r a t e o f m e t a b o l i s m i n y o u n g
g r o w i n g a n i m a l s ha s b e e n t h e s u b j e c t o f r e c e n t
i n t e n s e s t u d y . T h i s t o p i c w a s c o n s i d e r e d i n
d e t a i l b y W a t e r l o w e t a l. ( 1 0 5 ) . T h e y p r e s e n t e d
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1 1 3 2 MOE
e v i d e n c e f r o m r a t s t h a t p r o t e i n t u r n o v e r
d e c l i n e s w i t h a g e a n d t h a t p r o t e i n d e g r a d a t i o n
i s g r e a t e r i n a n i m a l s g r o w i n g m o r e s l o w l y .
E d m u n d s a n d B u t t e r y ( 3 0 ) p r e s e n t e d d a t a
s h o w i n g s u b s t a n t i a l d i f f e r e n c e s a m o n g s p e c i f i c
t i ss u e s in t h e f r a c t i o n a l r a t e ( p e r d a y ) i n p r o t e i n
s y n t h e s i s ; . 0 5 8 f o r l e a n t i s s u e , .4 7 5 f o r b r a i n ,
a n d i n t e r m e d i a t e r a t e s f o r o t h e r t i s s u e s . T h e y
a l so i n d i c a t e d t h a t t h e r a t i o o f s y n t h e s i s t o
d e p o s i t i o n w a s 3 : 1 . T h e c l a r i f i c a t i o n o f t h e r o l e
o f p r o t e i n t u r n o v e r i n t h e g r o w i n g a n i m a l
w i l l, h o p e f u l l y , b e o f c o n s i d e r a b l e v a lu e i n
p a r t i t i o n i n g e n e r g y c o s t s i n y o u n g g r o w i n g
c a t t l e .
A n o t h e r i m p o r t a n t f a c t o r i n i d e n t i f y i n g
e n e r g y n e e d s o f t h e g r o w i n g a n im a l i s t h e
e x t e n t t o w h i c h b o d y c o m p o s i t i o n i s i n f l u e n c e d
b y n u t r i t i o n a l m a n i p u l a t i o n . M a n y d i e t a r y
e f f e c t s h a v e b e e n s u m m a r i z e d c o n c i s e l y b y
B l a c k ( 1 2 ) f o r th e g r o w i n g l a m b . H i s d a t a
s u g g e s t t h a t a n i m a l s g r o w n a t h i g h e r n u t r i t i o n
w i l l h a v e h i g h e r b o d y f a t t h a n a n i m a l s g r o w n
m o r e s l o w l y a l t h o u g h t h e d i f f e r e n c e i n c o m -
p o s i t i o n b e c o m e s p r o g r e s s i v e l y l e ss as t h e
a n i m a l a p p r o a c h e s m a t u r i t y . P r o t e i n c o n t e n t o f
t h e b o d y i n c r e a s e d p r o g r e s s i v e l y a s p r o t e i n
c o n t e n t o f t h e d i e t ( p e r c e n t o f M E ) w a s i n-
c r e a s e d f r o m 6 % t o 1 0 , 1 5 , a n d 2 0 % . T h i s
r e s p o n s e t o p r o t e i n s t e a d i l y d e c l i n e d w i t h
i n c r e a s i n g b o d y w e i g h t . P r o t e i n a b o v e 1 0% o f
M E h a d l i , t l e e f f e c t o n c o m p o s i t i o n o f la m b s
w e i g h i n g o v e r 3 0 k g .
T y r r e l l e t a l. (9 1 ) p a r t i t i o n e d g a i n o f H e r e f o r d
h e i f e r s i n t o p r o t e i n a n d f a t b y c a r b o n a n d
n i t r o g e n b a l a n c e i n a n i m a l s in fa s t a n d w h e n
g i ve n m a i n t e n a n c e a n d a d l i ti b u m i n t a k e.
R e g r e s s i o n o f f a t d e p o s i t i o n o n t o t a l e n e r g y
d e p o s i t e d i n d i c a t e d t h a t 95 o f t h e c h a n g e i n
E B w a s f r o m c h a n g e i n f a t r e t e n t i o n a n d o n l y
5
f r o m c h a n g e i n p r o t e i n r e t e n t i o n .
T h e l i m i t a t i o n o f e n e r g y r e t e n t i o n a l o n e as
t h e e x p r e s s io n o f p r o d u c t i v i t y in g r o w t h is
a p p a r e n t f r o m r e s u lt s o f T y r re l l a n d W a l d o
( 9 3 ) a n d W a l d o a n d T y r r e l l ( 1 0 4 ) . I n c a l o r i-
m e t r i c a n d g r o w t h s t u d i e s t h e y f e d d i r e c t
c u t o r c h a r d g r a s s s i l a ge w i t h o r w i t h o u t a
m i x t u r e o f . 12 % f o r m a l d e h y d e a n d . 1 4% f o r m i c
a c i d . E a c h s i la g e w a s f e d a l o n e a n d s u p p l e m e n t e d
w i t h f o r m a l d e h y d e - t r e a t e d s o d i u m c a s e i n a t e
a n d f e d t o H o l s t e i n s te e r s . T r e a t m e n t o f t h e
s il ag e o r s u p p l e m e n t a t i o n w i t h c a s ei n i m p r o v e d
n i t r o g e n r e t e n t i o n b u t d i d n o t i n f l u e n c e e n e r-
g e t i c e f f i c i e n c y . I n c r e a s i n g i n t a k e o f i n s o l u b l e
p r o t e i n i n c re a s e d t h e p r o p o r t i o n o f g a in a s
p r o t e i n f r o m 3 8 t o 5 1 % o f t o t a l c a l o r i e s g a i n e d .
i s c r e t e E f f e c t s o n E n e r g y U s e
M a n y s o u r c e s o f e n e r g y l o ss a re i n c l u d e d i n
t h e d i s c u s s i o n o f e n e r g e t i c e f f i c i e n c y p r e s e n t e d
a b o v e . M a n y o f t h e s e h a v e b e e n s t u d i e d s p e c if i -
c a l ly , a n d t h e i n f o r m a t i o n g a i n e d h a s i m p r o v e d
o u r u n d e r s t a n d i n g o f t o t a l u se o f e n e rg y b y
c a t t l e . W e b s t e r e t a l . ( 1 0 7 ) d i s c u s s e d s e v e r a l
c o m p o n e n t s o f h e a t in c r e m e n t ( H I ) i n c l u d in g
t h e c o s t o f e a t i n g a n d r u m i n a t i n g , t h e h e a t
p r o d u c e d b y r u m e n f e r m e n t a t i o n , a n d t h e
i n c r e a s e d h e a t p r o d u c e d b y t h e t i s s u e s o f t h e
g u t a n d t h e l i v e r . H e c i t e d a r a n g e i n e n e r g y
c o s t s o f e a t i n g o f 2 . 5 c a l / k c a l M E f o r g r a ss
p e l l e t s a n d 3 6 c a l / k c a l M E f o r f r e s h g r a ss . H e
c o n c l u d e d t h a t t h e e n e r g y c o s t o f ru m i n a t i n g
c o u l d b e d i s c o u n t e d a s a c o n t r i b u t i o n t o H I.
W e b s t e r e t al . ( 1 0 8 ) e s t i m a t e d h e a t o f
f e r m e n t a t i o n i n
v ivo
i n sh e e p a n d f o u n d 6 8 c a l
h e a t p r o d u c e d p e r k i l o c a l o r i e o f d ig e s t i b l e
e n e r g y fr o m f o r a g e d i e ts . H e f o u n d n o d i f f e r e n c e
d u e t o d i e t s o u r c e in t h e a m o u n t o f h e a t
p r o d u c e d b y t h e t i ss u e s o f t h e g u t , b u t h e a t
p r o d u c t i o n i n c r ea s e d e x p o n e n t i a l l y w i t h i n-
c r e a s i n g M E i n t a k e . A t a n i n t a k e o f 1 4 3 . 4 k c a l
M E / k g T s, h e a t
produc t i on
i n t h e t i ss u e s o f t h e
g u t w a s 2 7 k c a l / k g Ts p e r 2 4 h . F a s t i n g h e a t
p r o d u c t i o n o f g u t t i s s u e s w a s 1 5 k c a l / k g v s.
T h e H I d u e t o f e e d i n g in t h e g u t w a s , t h e r e f o r e ,
1 2 k c a l / k g T s o f w h i c h 7 k c a l w a s f e r m e n t a t i o n
h e a t a n d 5 k c a l w a s a e r o b i c m e t a b o l i s m i n t h e
g u t t i s su e s . W e b s t e r e t a l. ( 1 0 7 ) c o n c l u d e d t h a t
p r o c e s s e s o f
ingest ion
a n d d i g e s t i o n c a n a c c o u n t
f o r a b o u t 2 5 t o 3 0 % o f t o t a l H I a n d t h a t m o s t
o f t h e v a r i a t i o n in t o t a l H I m u s t b e fr o m t h e
n a t u r e o f s u b s t r a t e s m a d e a v a i l a b l e b y d i g e s t i o n
a s s u g g e s t e d b y A r m s t r o n g a n d B l a x t e r ( 2 , 3) .
E n v i r o n m e n t a l t e m p e r a t u r e s i n f l u e n c e t o t a l
e n e r g y u s e i n s e v e r a l d i f f e r e n t w a y s . Y o u n g
( 1 1 2 ) r e v i e w e d e f f e c t s o f c o l d e n v i r o n m e n t o n
e n e r g y u s e a n d e m p h a s i z e d t h a t th e r m a l s tr e s s
is d e s c r i b e d t o o f r e q u e n t l y i n t e r m s o f t e m p e >
a t u r e a l o n e . H e c i t e s L e e ' s ( 4 9 ) c o m p i l a t i o n o f
e n v i r o n m e n t a l v a r ia b l e s ( t e m p e r a t u r e , h u m i d i t y ,
a ir m o v e m e n t , r a d i a t io n , p r e c i p i t a t i o n ) , a n i m a l
c h a r a c t e r i s t i c s ( s p e c i es , a g e a n d s e x , b r e e d a n d
t T p e , m e t a b o l i c s t a t e , c o a t , a c c l i m a t i z a t i o n ,
n u t r i t i o n a n d h y d r a t i o n , d e r a n g e m e n t a n d
d i s ea s e , i n d i v i d u a l v a r i a b i l i t y ) a n d c r i t e r ia o f
e f f e c t ( p r o d u c t i v i t y , g r o w t h , r e p r o d u c t i v i t y ,
Journa l of D airy Science Vol. 64, N o. 6 , 1981
8/11/2019 2010. Tema 10 - Material de Lectura 5 - Moe
14/20
METABO LISM - 75TH ANNIVERSARY ISSUE 1133
p h y s i o l o g i c a l r e s p o n s e , p a t h o l o g i c a l p a t t e r n s )
t o i l lu s t r a te t h e c o m p l e x i t y o f d e s c r i b i n g o r
p r e d i c t i n g e n v i r o n m e n t a l e f f e c t s . T h i s t o p i c is
c o v e r e d e x t e n s i v e l y in a s e p a r a t e p a p e r i n
t h i s i s s u e , s o I w i l l n o t p u r s u e t h e t o p i c h e r e .
M o s t e n e r g y m e t a b o l i s m r e s e a r ch h a s b ee n
u n d e r c o n d i t i o n s o f t h e r m a l n e u t r a l i t y s o
t h a t e n v i r o n m e n t a l e f f e ct s m u s t b e c o n s i d e r e d
i n a p p l y in g th e d a t a t o e x t r e m e c o n d i t i o n s . O n e
s p e c i f ic e f f e c t , h o w e v e r , s h o u l d b e m e n t i o n e d
h e r e b e c a u s e i t a p p e a r s t o o p e r a t e o v e r a w i d e
r a n ge o f e n v i r o n m e n t a l c o n d i t i o n s . T h is e f fe c t
i s a r e d u c t i o n i n d i g e s t i b i l i t y w i t h d e c r e a s i n g
t e m p e r a t u r e . Y o u n g ( 1 1 2 ) c i t e s s e v e ra l e x p e r i -
m e n t s i n w h i c h t h e m e a n r e d u c t i o n i n D M
d i g e s t i b i l i t y w a s 1 . 8 p e r c e n t a g e u n i t s p e r 1 0 C
r e d u c t i o n i n t e m p e r a t u r e . K e n n e d y e t a l. ( 4 5 )
r e p o r t e d t h a t d e c r e a s i ng t e m p e r a t u r e h a d t h e
e f f e c t o f i n c r e a s i n g r a t e o f p a ss a g e o f r u m e n
i n g e s ta , w h i c h d e c r e a s e d o r g a n i c m a t t e r d i ge s -
t i o n b u t i m p r o v e d e f f ic i e n c y o f s y n th e s i s o f
m i c r o b i a l p r o t e i n .
Improvements in Research Techniques
I n n o v a t i o n o r d e v e l o p m e n t i n r e l a t e d f ie l d s
h a s h ad a p r o f o u n d e f f e c t o n t e c h n i q u e s
a v a i l a b l e t o r e s e a r c h e r s i n e n e r g y m e t a b o l i s m .
I m p r o v e d s u rg i ca l t e c h n i q u e s a n d d e v e l o p m e n t
o f i n t e g r a t e d e l e c t r o n i c c i r c u i t s a n d i n e x p e n s i v e
c o m p u t e r s h a v e h a d a p r o f o u n d e f f e c t o n
c o l l e c t i o n a n d a n a l y s i s o f p e r t i n e n t d a t a.
R e c e n t r e vi e w s d o c u m e n t t h e d e v e l o p m e n t a n d
u s e o f s e v e r al t e c h n i q u e s .
T h e i n c r e a s e d u s e o f i n t e s t i n a l l y c a n n u l a t e d
a n i m a l s h a s a l l o w e d i d e n t i f i c a t i o n o f s i t e o f
d i g e s t i o n a n d d i s a p p e a r a n c e o f n u t r i e n t s
f r o m s p e c i f ic s e g m e n t s o f t h e g u t ( 5 1 ) . T h e
i n c r e a s e d a v a i l a b i l i t y a n d u s e o f m a r k e r s h a s
p e r m i t t e d s y s t e m a ti c s t u d y o f t h e d y n am i c s
o f f o o d p a r t i c l e d e g r a d a t i o n a n d p a s s a g e
t h r o u g h t h e g u t ( 33 ). M e t h o d s o f m e a s u r i n g
b l o o d f l o w h a v e b e e n u s e d t o m e a s u r e q u a n t i -
t a t i v e l y u p t a k e o f n u t r i e n t s f r o m t h e g u t ( 9 ,
4 8 ) . I m p r o v e d a n a l y t i c a l s e n s i t i v i t y a n d a u t o -
m a t e d a n a ly s i s h a v e i m p r o v e d t h e a b i l i t y t o
i d e n t i f y a n d q u a n t i f y i n t e r m e d i a r y m e t a b o l i t e s .
A s t h e s e m o r e
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