Cattle Growth and Composition

8/10/2019 Cattle Growth and Composition

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Agricultural Systems 361991) 17-41

Ev a lu a t io n o f Fo u r S imu la t io n Mo d e l s o f Ca t t l e Gro wthand Body Com pos i tion : Par t l I -- -S imu la t ion and

Co mp ar i so n wi th Ex p e r imen ta l Gro wth Da ta

R. N . Arnold* G. L. Bennett:~

U S D e p a r tm e n t o f A g r i c u lt u r e,

Clay Center, Nebraska 68933-0166, USA

R e c e iv e d 15 January 1990;r ev ised ver s ion r ece iveda n d a c c e p t e d 30 August 1990)

A B S T R A C T

Sim ulated results or cat tle grow th and body composi t ion o fou r m odels were

com pared with experimental ly measu red values fro m three experiments .Non e o f the models accurate ly est imated body composit ion. The models weremore accurate in estimating empty body weight than body composition.Expe rimental t reatments o f die tary energy intake, mature s ize, age, and sexwere not consistently misestimated in one direction among the threeexperim ents. The mod els did not predic t fe e d intake accurately. Using theintakes predicted by the models did not improve the predict ion o f bodycompo sition. Non e o f the ou r m odels wa s clearly superior. It is concluded thatuse of grow th curves a s im plemented in the fo ur models provides only anappro xim ation o f the compo sition o f a large group o f animals. Gro wth curvebas edm ode ls can result in up to 20 to 25 error in estimate s o f body growth.These m odels wo uld not be suitable in situations requiring close approx im-at ions o f body grow th and com posi tion fo r the simulat ion o f productionpractices. Ad ding de tailed or comple x logic to grow th curve based mo dels ma ybe o f li tt le value in improving accuracy. M or e detailed, me chanistic mod elsneed to be evaluated and growth model logic and level of aggregationappraised.

* Pre s en t a d dr es s: D e p a r tm e n t o f M e a tand Anim al Sc ience , 1675 Obs erva to ry Dr ive ,U n iv e r s i t y o f Wis c o n s in ,Madison 53706, USA.

P r e s e n t a d dr es s: R o m a n L . H r u s k a U S M e a t A n im a l R e s e a r c h C e n te r, A R S , U S D A , P OBox 166, Cla yC e n te r, N e b r a s k a 68933-0166, USA.

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8 R. N. Arnold G. L. Bennett

I N T R O D U C T I O N

C o m p a r i s o n o f fo u r c o m p u t e r iz e d g r o w t h m o d e l s f o r c a tt le s h o w e d t h a tm o d e l s p r e d i c te d d i f fe r en t c o m p o s i t io n , r a te s o f g a in , a n d i n t a k e (A rn o l d &Benne t t , 1989). W hi le these mo de l s d iffe r in s im ula t ing g row th , i t is no tk n o w n t o w h a t e x te n t th e s e m o d e l s p re d i c t o b s e rv e d g ro w t h p a t te rn s . Th efo u r g ro w t h m o d e l s w e re a t te m p t s t o d e s c ri b e th e p ro c e ss o f g ro w t h b y u s i n gg ro w t h c u rve s . L i m i t e d e v a l u a t i o n a n d u s a g e o f th e s e m o d e l s (N o t t e re t a l .1 9 7 9 a b c ; Sanders & Car twr igh t , 1979a ; Loewere t a l . 1983; Olt jene t a l .1986a) ind ica ted gene ra l app l i cab i l i ty, bu t mode l p red ic t ions need to bec o m p a re d w i t h e x p e r im e n t a l o b s e rv a t io n s t o d e t e rm i n e t h e u s e fu l n es s a n dl im i t a t io n s o f e a c h a p p ro a c h . Te s t in g t h e a c c u ra c y o f m o d e l s i n s im u l a ti n gg ro w t h a n d b o d y c o m p o s i t i o n h a s b e e n q u i t e l im i t e d b e c a u s e o f t h e la c k o fs u i ta b l e d a t a i n th e l i te r a tu r e . H o w e v e r, m o d e l e v a l u a t i o n is im p o r t a n t f o rfu t u r e d e v e l o p m e n t a n d u s e o f p ro d u c t i o n m o d e l s i n w h i c h a c c u ra t er e p re s e n t a t i o n o f c a t tl e g ro w t h a n d c o m p o s i t i o n i s a n e s s e n ti al c o m p o n e n t .Thu s , the ob jec t ive o f the p re sen t re sea rch w as to eva lua te the use fu lnes s o ft h e a l g o r i th m s u s e d in th e fo u r g ro w t h m o d e l s b y c o m p a r i n g s i m u l a t e d a n de x p e r im e n t a ll y m e a s u r e d g r o w t h a n d c o m p o s i t io n .

E VA L U AT I O N P R O C E D U R E S

escription of experim ental d ata

D a t a o n f e e d i n t a k e a n d b o d y c o m p o s i t i o n m e a s u re d b y t h e d i r e c t- s l a u g h t e rt e c h n i q u e f ro m e x p e r i m e n t s r e p o r t e d b y S i m p fe n d o r f e r ( 1 9 7 3 ) , A rn o l d(1980) , and C . L . Fe r re l l (unpub l i shed da ta , 1986 Mea t Anima l Resea rchC e n t e r) w e re u s e d t o e v a l u a t e f o u r g ro w t h m o d e l s. Th e s e e x p e r i m e n t s w e re

n o t u s e d t o d e v e l o p t h e g ro w t h m o d e l s .I n d i v i d u a l fe e d i n t a k e a n d c h e m i c a l a n a ly s i s o f b o d y c o m p o s i t i o n f ro m 3 9

s tee rs were ob ta ined f ro m C . L . Fe r re l l (unpub l i shed da ta , M A R C , 1986). Th ee x p e r i m e n t (FER ) c o m p a re d t h r e e f e e d in g r e g i m e n s , t w o le v els o f in t a k e ,t w o m a t u re s iz es o f ca tt le , a n d t h r e e p e r io d s o f g ro w t h . Th e f e e d in g r e g i m e n sc o n s i st e d o f a d l ib i t u m f e e d in g o f a m o d e ra t e - e n e rg y -d e n s e si la g e r a ti o n(7 4 % c o rn s ila g e, 2 0 % a lf a lf a h a y la g e , a n d 6 % s o y b e a n m e a l o n a d rym at te r bas is ), ad l ib i tum feed ing o f a h igh-en e rgy-d ense g ra in ra t ion (73-9%c o rn g r a i n , 2 0 % a l f a l f a h a y l a g e , a n d 5 6 % s o y b e a n m e a l o n a d ry m a t t e r

basi s) , and re s t r ic t ed feed ing o f the g ra in ra t ion . T he re s t ri c t ed l evel o f in takea p p ro x i m a t e d t h e m e t a b o l i z a b l e e n e rg y in t a k e o f t h e s te e rs c o n s u m i n g t h es il age ra t ion . A t the s t a r t o f each pe r iod , one an im a l f rom each d ie t by m a tu res iz e t r e a t m e n t c o m b i n a t i o n w a s p la c e d o n a n e a r m a i n t e n a n c e l ev e l o f


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omparison with experimental data 9

i n t a k e . T h e r e m a i n i n g a n i m a l s c o n t i n u e d t o r e c e i v e a d l i b i t u m l e v e l s o fi n t a k e. S m a l l m a t u r e s i z e s t ee r s w e r e p r i m a r i l y t w o - w a y c r o ss e s o f R e d P o l lo r A n g u s s ir es w i t h A n g u s o r H e r e f o r d d a m s . L a rg e m a t u r e s iz e s te e rs w e r ec r os s e s o f B r o w n S w i ss s ir es w i t h d a m s t h a t w e r e t w o - w a y c r o s se s o f A n g u s ,H e r e f o r d , S i m m e n t a l , L i m o u s i n , a n d C h a r o l a i s . I n it i al w e i g h ts o f t h e s m a l lan d l a rge ma tu re s ize s t ee r s we re 265 and 318 kg , re spec t ive ly. I nd iv id ua ls te e rs w e r e s l a u g h t e r e d a t t h e e n d o f e a c h g r o w t h p e r i od . T h e g r o w t h p e r i o d sc o n s i s t e d o f a p p r o x i m a t e l y 9 5 a n d 110 k g w e i g h t g a i n s f o r s m a l l a n d l a rg ema tu re s i ze s t ee r s f edad l ib i tum r e spec t i ve ly. The l eng th o f t he f i r s t twop e r i o d s v a r i e d f r o m 9 8 t o 131 d a y s w h i le th e l a st p e r i o d v a r i e d f r o m 1 90 to3 10 d a y s o w i n g t o t h e f e e d in g r e g im e n s i m p o s e d a n d t h e m a t u r e s iz e o f t h e

c a tt le . M a i n t e n a n c e a n d n o n m a i n t e n a n c e f e d st ee rs w e r e s l au g h t e r e d a t t h es a m e t im e s . Tw o s m a l l m a t u r e s iz e a n d t h r e e l a rg e m a t u r e s iz e s t ee r s w e r es l a u g h t e r e d a t t h e s t a r t o f t h e e x p e r i m e n t f o r a n e s t i m a t e o f in i t ia l b o d yc o m p o s i t i o n . Tw o d i g e s t ib i l it y t r ia l s i n v o l v i n g t o ta l f e ca l a n d u r i n ec o l l e c t i o n w e r e a l s o c o n d u c t e d w i t h a s e p a r a t e g r o u p o f 12 s te e rs t o e v a l u a t et h e n u t r i t i o n a l v a l u e o f t h e t w o r a t i o n s w h e n f e d a t t w o l ev e ls o f in t a k e .

I n d i v id u a l m e a s u r e m e n t s o f b o d y c o m p o s i t i o n o f 6 6 c a tt le w e re r e p o r t e dby S im pfe nd or f e r (1973). A ya l a (1974) p r e sen t ed f eed i n t ake fo r each o f t hesean im a l s a nd f eed eva lua t i on b y d iges t ib i l it y t ri al s. Th e e xpe r im en t (S IM) i n -

vo lved a f ac to r i a l de s ign cons i s t i ng o f two b reeds (A ngus an d Hol s t e in ) , t h r eetypes o f an im a l (bul ls , s tee r s, an d he i fe r s) , two l eve l s o f ene rgy i n t ake ( adl i b i t um an d 70% ad l i b i tum) , an d t h r ee pe r io ds o f g row th (63, 140 an d 224days) . A pel le ted rat ion con sis t ing pr im ari ly o f co rn (54-4%), oa t hul ls (20.0%),soybean mea l ( 12 6%) , a l f a l f a mea l ( 5 .0%) , and molas ses (5 -0%) was f ed .T h e a v e r a g e w e i g h t a t th e s t a r t o f t h e e x p e r i m e n t w a s 1 99 a n d 18 1 k g f o r t h eA n g u s a n d H o l s t e i n c a t t le , re s p e c ti v e ly. A t t h e s t a r t o f t h e e x p e r i m e n t , 18a n i m a l s w e r e s l a u g h t e r e d f o r a m e a s u r e o f in it ia l c o m p o s i t i o n . O n l y o n ea n i m a l w a s p l a c e d o n e a c h t r e a t m e n t e x c e p t t w o a n i m a l s w e r e a s si g n ed t o

e a c h t r e a t m e n t f o r t h e 2 2 4 - d a y g r o w t h p e r i o d w i t h A n g u s c a t t l e a n d f o rH o l s t e i n b u ll s. D a i l y f e e d i n t a k e f o r e a c h a n i m a l w a s c a l c u l a t e d b y f i t ti n g aq u a d r a t i c c u r v e t o t h e a v e r a g e f e e d i n t a k e s f o r t h e t h r e e p e r i o d s . T h ei n t e rc e p t o f e a c h c u r v e w a s a d j u s t e d s o t o t a l i n t a k e e s t i m a t e d f r o m t h e c u r v ew a s e q u a l t o t h a t a c t u a l l y c o n s u m e d b y e a c h a n i m a l . D i g e s t i b il i tym e a s u r e m e n t s b y t o t a l c o ll e c ti o n w e r e c o n d u c t e d w i t h e a c h a n i m a l a t t h ee n d o f e a c h p e r i o d .

T h e t h i r d d a t a s et (A R N ) c o n s is t ed o f m e a s u r e m e n t s o f b o d y c o m p o s i t i o nb y c h e m i c a l a n a ly s i s o f 26 H e r e f o r d - A n g u s c r o s s b r e d s t ee r s (A r n o l d , 1 98 0).

T h e f e e d i n t a k e d a t a a v a i la b l e i n t h i s s t u d y w e r e d a i l y p e n a v e r a g es . I n i t ia lw e i g h t a v e r a g e d 2 4 6 k g . S ix s t ee r s w e r e s l a u g h t e r e d a t t h e s t a r t o f t h ee x p e r i m e n t . T h e s te e rs r e c e i v ed e i t h e r a c o r n g r a i n r a t i o n ( c o n t a i n i n g 15 %c o r n c o b ) o r a c o r n s i la g e r a t i o n . A s o y b e a n m e a l b a s e d s u p p l e m e n t


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20 R. N . Ar n o l d , G . L . Be n n e t t

prov ided adeq ua te p ro t e in in bo th r a t ions . On e ha l f t he s tee r s on eachra t ion were implan ted wi th es t rad io l 17 /3 .

T h e m e a s u r e d e m p t y b o d y c o m p o s i t i o n a n d w e i g h t a n d a ct u a l d r y m a t t e rin t ake o f t he ca t tl e f ed d i b i t u m f o r th e t re a t m e n t c o m p a r i s o n s o f t h e t h re eexpe r imen t s a r e p r e sen t ed in Tab le 1 .

T A B L E 1

M e a s u r e d E m p t y B o d y C o m p o s i t i o n a n d W e i g h t o f a ll C a t t le a n d D r y M a t t e rI n ta k e o f C a t tl e F e d a d l i b i tu m f o r Tr e a t m e n t G r o u p s o f T h r e e E x p e r i m e n t s u s e d t o

E v a l u a te G r o w t h M o d e l s

Tr e a t m e n t P r o t e in ~ F a r Wa t e r + a s h a E B W a To t a l D M I ~

k g ) k g ) k g ) k g ) k g / h e a d )

F E RSila ge 65.9 72.6 2 26:5 365 2 181C or n 65 .4 87 .7 229 0 382 1 467R est r ic ted 64 5 66 .6 217 3 348 - -G ain 71.5 94 .7 242 .7 409 - -M ain ten an c e 5 9 .0 5 6 .6 2 05 8 3 21 - -Sm all 58-2 76.3 2 04.6 339 1 713La rge 72.4 75.0 243 .9 391 1 935Pe r 1 49 5 51.4 181.1 282 708Pe r 2 67 '4 75 '5 227 2 370 1 555Per 3 78 '8 100.0 264 '4 443 3 2 t 0

SE 3'3 4.6 8.1 16

S I MA d l i b 50 '5 62 .0 184 .2 297 - -Re st r ic ted 44 7 35-7 162 .5 243 - -A ng u s 46-7 57-8 168.3 273 831H oi s t 48 '6 39 '9 178 .3 267 880Bu ll 53.4 43.1 193.5 290 916

St eer 46.9 47.4 172.4 267 856H eife r 42 '6 56 1 154 0 253 795Pe r 1 37 '8 28-2 140-6 207 315Pe r 2 48 '9 48.2 178 0 275 835P er 3 56.2 70.2 201.4 328 1 418

SE 1,2 2.4 3.1 5

A R NSil age 67.8 140.3 244.4 452 2 141C o rn 68.7 146.1 241-2 454 1 976

Im pl an t 66.3 147.2 236 0 450 2 119

+ Im pla n t 70 .2 139 '2 249 .6 457 1 998S E 1.1 5.1 4.7 6

a C o r r es p o n d s to th e ca t t l e i n d ic a t ed in F ig s 3 , 4 , 5 , an d 6 .b C o r r e s p o n d s t o t h e c a t t l e i n d i c a t e d i n F i g . 7.


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esc r ip t ion o f g rowth m ode l s

G ro w t h m o d e l s d e s c r i b e d b y N o t t e r ( 1 9 7 7 ) (N O ) , Sa n d e r s & C a r t w r i g h t(1979b) (SA), Loeweret al . (1983, 1987) (LO), and Olt jenet al . (1986b). (OJ)were used to s imula te the th ree expe r imen ts . Arno ld & Benne t t (1989)p re v i o u s l y d e s cr i b e d th e fo u r m o d e l s a n d t h e n e c e ss a ry m o d i f ic a t io n s o f th em o d e l s. A d d i t io n a l m o d i f ic a t io n s w e r e n e c es s ar y fo r t h e N O m o d e l . T h e N Omode l accoun ted fo r he te ros i s e ffec t s in c ros sbred ca t t l e by dec reas ing thea g e a t i n f le c t io n t o 9 7 o f p u re b re d c at tl e a n d a d j u s t in g g ro w t h r a t ep a ra m e t e r s f r o m d a t a o f th e m a t u re , 4 0 0 -d a y a n d 5 5 0 -d ay w e i g h t s o f th ep u r e b r e d m i d p a r e n t . B e ca u s e t he s e d a t a w e r e l ac k in g fo r t h e F E R a n d A R N

e x p e r im e n t s , a l in e a r r e l a ti o n s h i p b e t w e e n t h e g ro w t h r a t e p a r a m e t e r s f o rc ro s s b re d c a t t l e a n d t h e i r m i d p a re n t v a l u e s w a s a p p ro x i m a t e d b y

K ' = 1 .0 25 x K (1 .0 4 3 0 5 - 0 .0 0 0 0 5 1 8 xW M A

w h e re K is t h e g ro w t h r a t e p a r a m e t e r f o r p u re b re d c a t t le a n dW M A is them a t u r e c o w w e ig h t.

A n a d j u s t m e n t f a c t o r f o r i n c r e a s i n g p ro t e i n s y n t h e s i s a f t e r h o rm o n ea d m i n i s t r a t i o n w a s o r i g in a l l y i n c o rp o ra t e d i n t h e O J m o d e l b u t w a s n o tu s e d i n th e p r e s e n t s i m u l a ti o n s . H a l f o f th e c a tt le i n th e A R N e x p e r i m e n tw e r e g i ve n h o r m o n e i m p l a n t s b u t n o n e w e r e a d m i n i s te r e d in th e F E R a n dSIM e x p e r i m e n t s .

Model s imula t ion procedures

T h e f o u r g r o w t h m o d e l s si m u l a te d g r o w t h a n d c o m p o s i t io n o f i n d iv i d u a la n i m a l s i n th e F E R , S I M a n d A R N e x p e r im e n t s us in g th e e x p e ri m e n t a ll ym e a s u r e d f e e d i n ta k e . A n i m a l s f eda d l i b i t u mw e re a l so s i m u l a t e d w i t h e a c h

m o d e l u s i n g t h e f e e d i n t a k e l o g i c i n c o rp o ra t e d i n t h e m o d e l s . Th i sc o m p a r i s o n e v a l u a t ed t h e c o m b i n e d a c c u r a c y o f p r e d ic t in g i n ta k e a n d t h eg r o w t h a n d b o d y c o m p o s i t i o n .

Th e p e r c e n t a g e d i g e st ib l e d ry m a t t e r o f t h e r a t io n s u s e d in t h e SA a n d N Om o d e l s w a s c a l c u l a t e d f o r t h e S I M a n d F E R e x p e r i m e n t s b a s e d o nd i g e st ib i li ty t ri a ls c o n d u c t e d i n th e s e e x p e ri m e n t s . Fo r t h e A R N e x p e r i m e n t ,t h e p e r c e n t a g e d i g e st ib l e d ry m a t t e r w a s c a l c u la t e d b a s e d o n N R C (1 98 4)f e e d v a l u e s b y s u b t r a c t in g 1 .2 5 t im e s t h e e t h e r e x t r a c t p e r c e n t a g e f ro m t h eT D N v a l u e o f t h e r at io n s . T h e v a l u e s o f n e t e n e rg y o f m a i n t e n a n c e a n d g a in

u s e d i n t h e O J m o d e l w e re c a l c u l a te d f ro m d i g e st ib i li ty tr ia l s in t h e S IM a n dF E R e x p e r i m e n t s a n d f r o m N R C ( 1 9 8 4 ) f o r t h e A R N e x p e r i m e n t . T h ec a l c u l a t e d v a lu e s fo r t h e m e t a b o l i z a b l e e n e rg y c o n t e n t w e re 2 -7 8 fo r t h e c o rng ra i n d i e t a n d 2 .5 0 M c a l / k g fo r t h e s il ag e d i e t i n t h e F E R e x p e r im e n t . Th e


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R. N. Arnold G. L. Bennett

me tabo l izab le ene rgy va lues o f these d ie ts w ere 2.61 fo r the co rn g ra in d ie tand 2 .62 fo r the s i l age d ie t when fed a t ma in tenance . The me tabo l izab lee n e rg y c o n t e n t o f t h e d i e ts f e d i n t h e S IM e x p e r i m e n t w e re 2 .5 1 M c a l /k g . I nt h e A R N e x p e r im e n t , th e m e t a b o l iz a b l e e n e rg y c o n t e n t w a s 2 .8 9 M c a l / k gfor the co rn d ie t and 2 .53 M ca l /kg fo r co rn s il age . Th e sup p lem ent fed wi tht h e c o rn d i e t h a d a m e t a b o l iz a b l e e n e rg y c o n t e n t o f 2 -5 1 M c a l / k g w h i l e th em e t a b o l i z a b l e e n e rg y c o n t e n t o f t h e s u p p l e m e n t f e d w i th t h e c o rn s ila g ec o n t a i n e d 2 3 9 M c a l o f m e t a b o l i z a b le e n e rg y p e r k g o f d ry m a t te r. T h e f ee danalyses for ce l l wal ls and ce ll con tents of feeds tuffs g iven in the B E E FS 156p ro g ra m w e re u s e d i n t h e LO m o d e l f o r t h e t h r e e e x p e r i m e n t s . Th ec o m p o s i t i o n o f c ell w a l ls a n d c ell c o n t e n t s o f c o rn c o b w a s c a l c u l a te d b y

d i ff e re n ce b e t w e e n e a r c o rn a n d c o rn g r a i n b y a s s u m i n g e a r c o rn c o n t a i n s25% cob on a d ry ma t te r bas i s . For o the r ingred ien t s no t g iven (a l fa l fahay lage , molas ses , oa t hu l l s, mine ra l s) , ana lyses were ca lcu la ted f rom N R C(1971, 1984).

The ind iges t ib le feed ene rgy va lues fo r ca rbo hy dra te an d p ro te in used int h e B EEFS1 5 6 p ro g ra m w e re t o o l o w fo r t h e r a t i o n s f e d i n t h e t h r e eexpe r im en ts and , thus , w ou ld p rod uce low in tak e e s tima tes . Ind iges t ib le feede n e rg y v a lu e s fo r c a rb o h y d ra t e , p ro t e in , a n d e t h e r e x t r a c t w e re c a lc u l a t e dfo r each ra t ion used in the th ree expe r imen ts f rom regres s ion re la t ionsh ips

presen ted by Schne ide r & F la t t (1975) . Feed c rude p ro te in , c rude f ibe r,n i t rogen f ree ex trac t, and e the r ex t rac t d iges t ion coe ffi c ien t s were e s t ima tedf ro m p ro x i m a l a n a ly s e s o f th e r a t i o n i n g red i e n ts . Th e r a t io n s w e re a n a l y s e dfo r t h es e c o m p o n e n t s i n t h e S IM e x p e r i m e n t b u t , ex c e p t f o r c ru d e p ro t e i n ,va lues f rom NRC (1984) had to be used in the o the r two expe r imen ts .Carbohydra te d iges t ib i l i ty was e s t ima ted a s the combined d iges t ib i l i ty o fc rud e f ibe r and n i t rog en f ree ex t rac t . Th e pe rc en tag e o f ind iges t ib le ene rg ywas then ca lcu la ted us ing the ene rg y con ten t s o f p ro te in , e the r ex t rac t, andc a r b o h y d r a t e f r o m t h e B E E F S 1 5 6 p r o g r a m .

R e g re s s io n e q u a t i o n s w e re d e r i v e d f ro m t h e e x p e r i m e n t a l d a t a t o e n a b l ees t ima t ion o f gas t ro in te s t ina l f ill o f each an im a l . L in ea r reg res s ionre l a t i o n s h i p s w e re c a l c u l a t e d u s i n g e x p e r i m e n t a l l y m e a s u re d l i v e b o d yw e i g h t s a n d e m p t y b o d y w e i g h ts o f in d i v i d u a l a n i m a l s f ro m i n it ia l s la u g h t e rg ro u p s a n d f in a l s l a u g h t e r g ro u p s . I n t h e F E R d a t a s et, t h r e e e q u a t i o n s w e red e r i v e d b a s e d u p o n t h e t h r e e d i e t a ry t r e a t m e n t s f e d . Fo u r e q u a t i o n s w e reo b t a i n e d fo r t h e S IM d a t a fo r t h e b r e e d -b y -d i e t c o m b i n a t i o n g ro u p i n g s .Fo u r e q u a t i o n s w e re d e r i v e d fo r t h e d i e t -b y - i m p l a n t g ro u p i n g s w i t h e a c he q u a t i o n r e p re s e n t i n g a s in g le p e n fo r th e A R N d a t a . S t a r ti n g e m p t y b o d y

c o m p o s i t i o n o f e a c h a n i m a l w a s e s ti m a t e d b y m u l t ip l y i n g th e p e r c e n t a g ec o m p o s i t i o n o f c o m p a ra b l e i n it ia l s la u g h t e r a n i m a l s b y t h e r e g res s io ne q u a t i o n e s t i m a t e s o f e m p t y b o d y w e i g h t . Th e s e d e r i v e d e s t i m a t e s o f


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Comparison with experimental data 23

gas t ro in t e s t i n a l t r ac t f ill we re u sed i ns t ea d o f t he f ill e s t ima t e s o r i g ina l l yi n c o r p o r a t e d i n t h e m o d e l s . T h e c o m p a r i s o n o f t h e N O a n d S A m o d e l s ,

w h i c h s i m u l a t e liv e w e i g h t i n s te a d o f e m p t y b o d y w e i g ht , w i t h t h e O J a n dL O m o d e l s s h o u l d b e m o r e u n b i a s e d u s i n g th is p r o c e d u re .To a c c o u n t f o r th e d i ff e re n c e s i n m a t u r e w e i g h t b e t w e e n t h e v a r i o u s

b r e e d s o f t h e a n i m a l s u s e d i n t h e t h r e e e x p e r i m e n t s , d a t a p r e s e n t e d b yC u n d i f fe t a l . ( 19 86 ) w e r e u s e d t o e s t i m a t e m a t u r e c o w w e i g h t s o f t h e p u r e -a n d c r o s s b r e d c a tt le . T h e m a t u r e c o w w e i g h ts f o r th e m a j o r i t y o f th e b r e e dc o m b i n a t i o n s in t h e t h r e e e x p e r i m e n t s w e re : 53 1 k g f o r R e d P o l l x A n g u s ;5 3 5 k g f o r A n g u s ; 5 3 9 k g f o r R e d P o l l H e r e f o r d ;5 5 5 k g f o r A n g u s xH e r e f o r d ; 5 7 4 k g f o r B r o w n S w is s x ( L i m o u s i n H e r e f o rd ) ; 5 8 0 k g f o r

B r o w n S w is s x ( S i m m e n t a l x A n g u s ) ; 5 8 4 k g f o r B r o w n S w is s x( S i m m e n t a l x H e r e f o r d ) ; 6 01 k g f o r B r o w n S w i ss ( C h a r o l a i s x H e r e f o r d ) ;6 0 7 k g f o r H o l s t e i n . T h e a c t u a l m a t u r e w e i g h t u s e d i n t h e s i m u l a t i o n o f e a c ha n i m a l w a s a d j u s t e d p r o p o r t i o n a l t o t h e m a t u r e w e i g h t a s d e f i n e d f o r am e d i u m m a t u r e s iz e c o w i n e a c h m o d e l a s d e sc r ib e d p r e v i o u sl y ( A r n o l d &B e n n e t t , 19 89). T h e s a m e f a c t o r a s u s e d i n th e S A a n d N O m o d e l s o f t h em a t u r e w e i g h t o f b u l ls a n d s t ee r s b e in g 1 5 t i m e s t h e m a t u r e w e i g h t o f c o w sw a s i n c o r p o r a t e d i n to t h e O J a n d L O m o d e ls . A n e s ti m a t e o f m a t u r e e m p t yb o d y w e i g h t f o r u s e i n t h e O J a n d L O m o d e l s w a s o b t a i n e d b y a s s u m i n g th a t

t h e m a t u r e c o w w e i g h ts ( C u n d i f f e tal . 1986) co nt a i ne d 14 5% gu t fill (Fer re l l& Jenkins , 1984) .

odel evaluation procedures

D e v i a t io n s b e t w e e n e x p e r i m e n ta l ly m e a s u r e d a n d m o d e l s i m u l a te d e m p t yb o d y w e i g h t a n d e m p t y b o d y c o m p o s i t i o n o f e a c h a n i m a l w e r e ca l cu l at e d b ys u b t r a c t i n g e x p e r i m e n t a l r e s u lt s f r o m s i m u l a t e d r es u lt s . T h e d e v i a t i o n s f o r

t h e f o u r m o d e l s w e r e c o m b i n e d w i t h i n e x p e r i m e n t a n d s ta ti st ic a ll y a n a l y s e du s i n g a s pl it p l o t a r ra n g e m e n t . T h e t r e a t m e n t s u s e d in t h e e x p e r i m e n t s m a d eu p t h e m a i n p l o t w i t h u p t o t h r e e - w a y i n t e r a c ti o n s in c l u d ed . T h e s u b p l o tc o n s i s te d o f t h e m o d e l s a n d u p t o t h r e e - w a y i n t e ra c t i o n s o f th e m o d e l s w i tht h e m a i n t r e a t m e n t e ffe cts . T h e G L M P r o c e d u r e o f S A S ( 19 85 ) w a s u s e d t oc o m p a r e m o d e l s w i t h i n t r e a t m e n t e ff ec ts a n d t o c o m p a r e r e su l ts b e t w e e n t h ee x p e r i m e n t a l t r e a t m e n t s w i t h in e a c h m o d e l . T h e s t a n d a r d e r r o r o f e a c hm e a n w a s u s e d t o d e t e r m i n e w h e t h e r d e v i a ti o n s w e r e di ff e re n t f r o m z e ro . T h ed e v i a t i o n s o f t h e s i m u l a t e d r e s u lt s o f t h e m o d e l s f r o m t h e e x p e r i m e n t a l lyo b s e r v e d v a l u e s a re p r e s e n t e d a s a p e r c e n t a g e o f t h e m e a n o f t h ee x p e r i m e n t a l l y m e a s u r e d v a l u e in b a r g r a p h s w i t h s t a n d a r d e r r o r b a r s t oshow s t a t i s t i ca l s i gn i f i cance o f t he dev i a t i ons .


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24 R. N. Arnold G. L. Bennet t

R E S U LT S

i m u l a t i o n s w i t h m e a su r e d i n t a k e

All m ode l s e s t ima ted ex pe r ime n ta l re su l ts wi th in 10 to 15 % w hen a ve ragedo v e r a l l a n i m a l s w i t h i n e a c h e x p e r i m e n t a n d t h e n a v e ra g e d a c ro s sexpe r imen ts (F ig . 1). N on e o f the m ode l s we re c lea r ly supe r io r, b u t them ode l s d i ffe red in the i r mispred ic t ions . W i th in expe r imen t (F ig . 2 ), ove r8 0 % o f th e m o d e l s i m u l a t io n s o f t h e v a r io u s c o m p o n e n t s w e re d i ff e re n t(P < 0 .0 5) f ro m t h e e x p e r i m e n t a l r es u lt s. Th e N O m o d e l u n d e re s t i m a t e d(P < 0 .0 5) e m p t y b o d y w e i g h t in a l l t h r e e e x p e ri m e n ts . Th e SA m o d e l

ove re s t ima ted p ro te in and un de re s t im a ted w a te r p lus a sh (P < 0 05) in a lle x p e r i m e n t s a n d t h e LO m o d e l u n d e re s t i m a t e d (P < 0 .0 5) w a t e r p l u s a sh a n de m p t y b o d y w e i g h t f o r a ll e x p e r im e n t s . Em p t y b o d y w e i g h t w a s g e n e ra l lymispred ic ted to a l e s se r ex ten t than body compos i t ion in a l l th reee x p e r im e n t s . Th e p o t e n t i a l d e g re e o fm i s p re d i c t i o n o f p ro t e i n a n d w a t e r p l u sa s h w o u l d a p p e a r t o b e 1 5 t o 2 0 % a n d t h a t o f f a t 2 0 t o 4 0 % w h e n u s in g a n yo f th e fo u r m o d e l s. P r e d i c ti o n o f p e r c e n t a g e c o m p o s i t i o n m a y b e a c c u ra t ef o r s i t u a t i o n s i n w h i c h b o d y c o m p o n e n t a n d e m p t y b o d y w e i g h t a r em i s p re d i c t e d t o t h e s a m e e x t e n t b u t t h e a b s o l u t e d e v i a t i o n w o u l d b e

mispred ic ted fo r bo th . Th i s s i tua t ion d id no t occur ve ry f requen t ly, thus ,p e r c e n t a g e c o m p o s i t i o n w o u l d n o t b e e x p e c t e d t o b e a n y m o re a c c u ra t e l yp re d i c te d t h a n t h e a b s o lu t e w e i g h t s o f c o m p o n e n t s . Th e N O m o d e l w a s b e sti n s i m u l a t i n g p ro t e i n a n d w a t e r p l u s a s h b u t w a s m o re v a r i a b l e b e t w e e ne x p e r i m e n t s t h a n t h e o t h e r m o d e l s in s i m u l a t i n g e m p t y b o d y f a t.

T h e d i r e c ti o n o f b ia s in p r e d i ct io n o f b o d y c o m p o s i t io n a n d e m p t y b o d yweigh t fo r t r ea tm en ts (F igs 3 to 6 ) was the s am e as the ove ra l l b ia s fo r each

~ / ' / / / / / / , . , ' )

O J

N O

S A

L O

[ ] P R T iI FAT

WAT E R

E W

/ / / / / / / Z

2 ~ 1 0

|

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1 0 2 0

M I S E S T I M AT I O N

Fig 1 The extent of misestimation in simulating experimentally measured empty body andchemical weights of cattle by four growth models when averaged across three experiments


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FER (34) OJC

SIM 148) I

[ ] m O T FAT

[ ] WATER ~I ~ . ~ARN (20) ~ W

. , . , --60 -40 -20 20

MISESTIMATION

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40 60

FER (34)

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I~ PROT[] FAT WATER[ ] B B W

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FER (34)

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LO

[ ] PR T FAT

[ ] WATER BBW

20 40 608 0 - 4 0 . 2 0 0 20 40 60 60 40 .20

MISESTIMATION MISESTIMATION

Fig. 2. The averag eexten t of misestimation n simulatingexperimentallymeasured growthand com position of cattle by four grow th models for three experiments.

exp e r im en t (F ig . 2 ) fo r 79 % , 69 % , 70 % an d 83 % of the 96 p red ic ted v a lues(4 b o d y c o m p o n e n t s x 1 4 t r e a t m e n t s ) f o r t h e O J , N O , SA a n d LO m o d e l s ,r e sp e c ti v el y. Th e b i a s e s in e s t i m a t i n g e m p t y b o d y c o m p o s i t i o n fo r t h ev a r i o u s t r e a t m e n t g ro u p i n g s d i f f e r e d m o re b e t w e e n e x p e r i m e n t s t h a nb e t w e e n t r e a t m e n t s w i t h i n a n e x p e r i m e n t . Th e re w a s n o e x p e r i m e n t a lt r e a t m e n t g ro u p t h a t w a s c o m m o n t o a l l t h r e e e x p e r i m e n t s b u t s e v e ra lt r ea t m e n t s w e r e c o m m o n t o t w o e x p e ri m e nts . C o m m o n t r ea t m e n t s

p ro v i d e d a c o m p a r i s o n fo r c o n s t a n c y o f bi as i n e s t im a t i n g w e i g h t g a i n a n db o d y c o m p o s i t i o n a c ro s s e x p e ri m e n t s . I f b ia s es a r e o p p o s i t e b e t w e e ne x p e r i m e n t s, t h e n e x p e r i m e n t a l c o n d i t i o n s o r m o d e l i n p u t s d i ff er e d b e t w e e ne x p e r i m e n t s a n d i n d i c a t e th a t t h e m o d e l s v a ry i n t h e i r a b il it y t o p r e d i c t ag iven s i tua t ion .

Th e O J , N O a n d SA m o d e l s p ro d u c e d le ss p o s it iv e d e v i a t io n s (P < 0 .0 5)fo r f at a n d e m p t y b o d y w e i g h t f o r st ee rs f ed th e c o rn g r a i n d ie t c o m p a re dw i t h t h e s il ag e d i e t i n th e F E R e x p e r i m e n t b u t t h is w a s r e v e r se d in t h e A R Ne x p e r i m e n t (F i g s 3 t o 6 ) . Th e d e v i a t i o n s i n e s t i m a t e d f a t a n d e m p t y b o d yw e i g h t f o r g r a i n a n d s il ag e d ie ts f o r t h e O J , N O , a n d SA m o d e l s w e re s im i l a rw h e n a v e ra g e d a c ro s s t h e tw o e x p e r im e n t s . Av e ra g e d ry m a t t e r i n t a k e w a ss imi la r fo r the ca t tl e on the s i lage an d g ra in d ie ts in the A R N expe r imen t (8 3and 8 .4 kg /hea d /day , re spec tively ). Ho w ever, s tee rs fed s il age consu m ed m ore


10/25

26 R. N. Arnold G. L. Bennet t

S I L A G E 1 2 )

C O R N 1 2 )

RESTR I O)

G A I N 1 8 )

M A I N T 1 6 )

S M A L L 17 )

L A R G E 17 )

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F E R.-L

~Ezzz=: m

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q

m l ~

S I M

A D L I B 2 4 )

R E S T R 2 4 )

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STEER 14)

H E I F E R 1 4 )

P E R I 1 4 )

P E R 2 1 4 )

PER 3 2 0 )

F ig 3

S I L A G E 1 O )

CORN I O)

- I M P t O )

, I M P I O )

- 6 0

-c

A R N

[ ] P R O T ~ i ~

I I FAT

[ ] WATER ,.~

E B W , - ~

- 4 0 - 2 0

miD

0 2 0 4 O 8 0


T h e a c c u r a c y o f th e O J m o d e l i n si m u l a t in g m e a s u r e d g r o w t h a n d c o m p o s i t i o n o fc a t t l e f o r v a r i o u s t r e a tm e n t g r o u p s o f t h r e e e x p e r im e n t s


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S I L A G E ( 1 2 )

CORN ( 12 )

RESTR ( 1O)

G A I N ( 1 8 )

M A I N T ( 1 6 )

S MA L L (1 7 )

L AR G E ( 1 7 )

PER 1 ( 1O )

PER 2 ( 1 2 )

PER 3 (12)

F E R

, i i

P

r J J f f f 1 ~ 4

, . I I

,I.

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14

I

I

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A D L I B ( 2 4 )

R E S T R (2 4 )

A N G U S (2 4 )

H O L S T (2 4 )

B U L L ( 2 0 )

S T E E R (1 4 )

HEIFER (I 4 )

PER 1 14)

P E R 2 (1 4 )

P E R 3 (2 0 )

Fig 4

S IL A G E (1 0 )

CORN ( I O)

- I M P t O )

+ I M P 1 O )

A R N

[ ] P R O T FA r[ ] WATE R ~ ~ E BW -c :

6 0 4 0 -20

I I - -

0 2 0 4 O 6 0


The accuracy of the N O model in simulating measured growth a nd composition ofcattle for various treatment groups of three experiments


12/25

28 R. N. Arnold G. L. Bennett

S I L A G E ( 1 2 )

C O RN ( 1 2 )

RESTR ( I O)

G A I N ( 1 8 )

M A I N T ( I 6 )

SM ALL ( 1 7 )

L A R G E ( 1 7 )

P E R I ( 1 0 )

P E R 2 ( 1 2 )

PER 3 ( 1 2 )

F E R

,,d

1

I

B ~I P

I,,

r

S I MA D L I B ( 2 4 )

R E S T R ( 2 4 )

A N G U S ( 2 4 )

H O L S T ( 2 4 )

B U L L ( 2 0 )

S T E E R ( 1 4 )

H E I F E R ( 1 4 )

P E R 1 ( 1 4 )

P E R 2 ( 1 4 )

P E R 3 ( 2 0 )

Fig 5

S I L A G E ( 1 0 )

C O R N ( 1 0 )

- I M P ( I O )

* I M P ( I O )

A R N =

[ ] PRO T '-:::[ ] FAT[ ] WAT E R E S w

- 6 0 - 4 0 - 2 0

Ih

0 2 0 4 0 6 0


T h e a c c u r a c y o f th e S A m o d e l i n s im u l a t in g m e a s u r e d g r o w t h a n d c o m p o s i t i o n o fc a t t le f o r v a r i o u s t r e a tm e n t g r o u p s o f t h r ee e x p e r im e n t s


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S I L A G E 1 2 )

CORN 1 2 )

RESTR I O)

GAIN 1 8 )

M A I N T 1 6 )

S M A L L ( 1 7)

LARGE 1 7 )

PER I 10 )

PER 2 12 )

PER 3 1 2 )

F R

e : / f / / 1 / .

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Cattle Growth and Composition