Un abordaje a la Historia
25 Esta observación, el modo de cazar que denomina chaco, voz quechua,
1 24
S e l e ct i on o f r a n g y steers resu l ted i n i n c rea sed beef p ro
d u c t i on ( y i e l d o f l ea n mea t) i n A n g u s , Beef S h o rt h o rn a n d Here ford s tee rs w h en compa red t o s hort-ty p e stee r s of t h ese b reed s . T h e re was , howeve r , con s i d e ra b l e v a r i a t i on i n ca rc a s s compos i t ion
i n each type g ro u p .
T h e ma i n reason f o r t h e i n c reased y i e l d o f l ea n beef was the s u pe r i or i n i t i a l I i v ewe i g h t o f ra n g y steers w h e n se l ected at w e a n i n g . A secon d a ry rea son , of eq u a I i mportance to t h e f i rst
i n Bee f S hort h o r n a n d Hereford types , w a s t h e m o r e rap i d g row th rate o f rangy steers , w h i ch ( b eca u s e o f t h e exper i menta l d e s i g n ) , re s u l ted i n r a n g y stee r s be i ng ovG r - f i n i s hed . Th i s a d ve r s e l y
a f f ecte d t h e i r ca rca s s compos i t i on , b u t w h e n t h e d a ta w e re cor rected for " n o rma l " ca rca s s vJ e i g h t / compo s i t i on re l at i on s h i p s t h e re w a s
I i tt l e d i f f e rence i n t h e a verage compos i t i on o f t h e t y p e g rou p s . Dou bt i s cast on t h e va l i d i ty o f s u c h a n a n a l y s i s o f cova r i a n ce b ec a use o f t h e sma l I r a n g e of we i g h t w i th i n each type g roup a n d t h e ext ra po l at i on ov e r t h e w i d e r r a n g e o f w e i g ht t h a t ex i sted b etween types .
Obv i ou s l y i f t y p e i s a s soc i ated w i t h g rowt h rate t hen s l a ug h t e r a t a constant age wo u l d n e cessa r i l y r e s u l t i n we i g h t d i f f e rences and we i g h t re l ated c h a n ges i n compos i t i on . T h e a n a l y s i s o f eo va r i a n c e i g no red t h i s t act . S e r i a l s l a ug ht e r of r a n d om l y c hosen steers i n each t y p e g ro u p wou I d have p rov i d ed a " b etter11 est i mate
I n c rea s ed y i e l d of b ee t i n r a n g y A n g u s steers w a s not re l ated to growth rate ( no sig ni f i ca nt d i f f e r e n ce b etween t y pes ) but was
re l a ted to s e l ect i on o f heav i er steers a t wea n i ng . A seconda ry rea son for i n c reased beet p rod uct i on i n A n g u s steers w a s t h a t ra n g y stee r s were l ea n e r t h a n s hort stee rs . D i f f e re n ces i n com pos i t i on between t y p es w e r e not l a rg e , mos t b e i ng l es s t h a n two p e rcentage u n i t s . T he re w a s con s i d e ra b l e v a r i a t i on i n compos i t i on a n d ca rca s s d i me n s i on s w i t h i n each t y p e .
T h e study p rov i d es ev i d en ce t h a t v i s u a l s e l ect i o n f or rangy ,
la te r-mat u r in g t y pes of steer s , w i I I i mp rove p rod u ct i o n i n t h e main b ee f b reed s i n New Zea l a n d . T h e t r e n d i s i n t h e r i g h t d i rect i on altho u gh i mp rovemen t i n terms o f carcass compos i t i on ma y not b e large, a n d t he reasons f o r i n c rea sed p roduct i on various .
T he i mporta n ce of h ea v y w ea n i n g we i g h t a n d its e f f ect on s u b s e q u e n t g rowt h and f i nal w e ight h a v e been rev i ewed b y P resto n a n d W i I I is ( 1 97 4 ) .
Facto rs know n to a f f ect wea n i n g w e i g h t w e re rev i ewed b y Preston a n d W i I I i s ( 1 9 7 4 ) , Nico l I ( 1 9 7 5 ) a n d A n d e rson ( 1 9 7 7 ) .
N i co l I showed t h a t va r i at i on i n a ge at wean i ng acco u n ted f o r u p to 4 1 . 9% o f va r i a t i on i n wea n i ng we i g h t i n 7 , 7 70 H e re f o r d wea n e r s a n d 35 . 5% i n 1 6 , 665 A ng us w ea n e r s . Sex w a s t h e n ext most i mportant sou rce of v a r i at i on . V a r i at i o n between h e r d s accou nted f o r 1 5 . 6 a n d
1 5 . 0% o f v a r i at i on i n w e a n i ng we i g h t , r e s pect i ve l y . Oth e r ma i n e f f ects ( ag e of d am , yea rs ) a cco u nted f or l es s t h a n
1 0%
o f v a r i at i oni n wea n i ng w e i g h t a n d most i n t eract i on s les s t h a n 2 % . T h e h erd x
yea r i nt e ract i o n acco u n ted t o r 1 9 . 1 a n d 1 9 . 5% o f w e a n i n g w e i g h t v a r i at i on i n Here f o rd a n d A n g u s h e rd s .
1 26
Ken n e d y a n d Hen d e r son ( 1 975 ) reported t h at h e r d s acco u nted f o r 24 to
4 1 %
o f va r i at i on i n wea n i n g we i g ht and f rom 3 1 to 4 4%of v a r- i a t i on i n yea r ! i n g we i g ht w h i l e o t h e r f a ctor s ( yea rs , s i r-es , yea r - h erd , yea r-s i re ) a c co u nted f o r l es s t ha n
1 0%
o f v a r i a t i on i nw_ea n ing w e i g h t . Ever i tt , J u ry a n d lrJ a r d ( 1 9 7 5 ) s howed a h i g h l y s i g n i f i ca n t e f f ect o f p re-t ra n s f e r e n v i ronmen t s on t h e s u b s eq u e n t w e i g h t s o f F r i es i a n , H e r e f o r d x F r i es i a n a n d S i mme n t a l x F r i es i a n steers wh i c h were g ra z e d on d i f f erent f a r ms to 1 6 weeks o f �ge t h e n t ra n s f e r red to a common e n v i ronmen t . On average 97% o f t h e d i f f e rence i n t r a n s f e r I i v ewe i g ht p e r s i sted a y ea r l at e r .
Between h e r d d i f f e rences a re so u rces of v a r i a t i on i n w ea n i n g we i g h t i n t h e A n g u s ( T r i a l X I ) a n d Beef S h ort h o r n t y p e s , b u t not i n t h e
A n g u s ( T r i a l X ) a nd Here f o r d t y p e s . Age , s i re a n d d a m e f f ects w e re
u n kn ow n . Ba rton ( 1 967 ) a n d P reston a n d W i I I i s ( 1 9 7 4 ) rev i ewed
t h e s u bj ect of I i ve a n i ma l j u d geme n t a n d f o u n d t h a t mo re " exp e r i e n c ed " p e rsons w e r e a b l e to d i s c e r n b etween co n f o rmat i on ty p es to a g reate r extent -t- h a n l es s " ex p e r i enced " o n e s .
I n t h e p resent exp e r i me n t t h e catt l e were se l ected by expe r i enced catt l emen , b ut a s ea ch t y p e w a s se l ected ( w i t h i n a b reed ) b y d i f f e rent peop l e t h e o p p o rt u n i ty ex i sted f o r d i f f e r e n t
i nt e r p retat i on s o f s h a p e b ut t h i s i s a n u n known f a ctor h e r e .
T hese resu l t s w i I I b e o f u s e to catt l emen w ho h a ve to se l ect steers w i t h o u t acce s s to p e r f o rma nce reco r d s o r I i vew e i g ht mea s u re men t s . S uc h p u rc ha ses occ u r ma n y t i mes d a i l y t h ro u g h o u t New Zea l a n d a t sa l eya r d s a n d o n f a rms w h e n store c a t t l e a r e bou g h t so l e l y o n t h e b a s i s o f v i s u a l a p p ra i sa l .
l t i s s ug g e sted t h a t w h e re p o s s i b l e t he v i s ua l a s se s sment of steers s ho u l d be ma d e i n con
j
u n ct i on w i t h p er forman c e r eco r d s to eva l uate a n i ma l s on t h e b a s i s o f pe r f o rma n c e cha racte r i st i c s1 28 REFERENCES
A b ra ha m , H . C . , Ca r p e nt e r , Z . L . , King, G . T . a n d But l e r , 0 . D .
( 1 968 ) . Re l at i on s h i p s o f ca rca s s we i g ht , con f o rmat i on a nd ca rca s s mea s u reme n t s a n d t h e i r u s e i n p red i ct i n g b e e f ca rca s s c u t a b i l i ty . J . A n i ma l Sc i . 604-6 1 0 .
A I ! d e n , W . G . ( 1 97 0 ) . T h e e f f ec t s o f n u t r i t i on a l d ep r i vat i on on t h e s u b s eq u e n t p ro d u c t i v i ty o f sheep a n d catt l e . N u t r i t i on A b s t r a c t s a n d Rev i ews 4 0 : 1 1 67- 1 1 84 .
A n d e r s e n , B . B . ( 1 9 7 7 ) . ( Genet i c i n v e s t i gat i on s on g rowt h , body d eve l opme n t a n d f ed ut i l i z at i on i n d u a l p u rpose c a tt l e . )
Beret n . Statens No . 4 4 8 .
A n d e rson , W . J . ( 1 97 7 ) . Inf lu e n ce o f p l a ne o f n u t r i t i on on t h e p rod u ct i v i ty o f A n g u s h e i f e r s : Master o f Sc i ence
T h e s i s 1 9 1 p p .
Anon ymo u s ( 1 966 ) . A compa r i son o f t h e g rowt h o f d i f f e rent t y p e s of catt l e f o r b e e f p ro d u c t i on . Report o f maj o r b ee f resea rch p roj ect . Roy a l Sm i t h f i e l d C l u b , Lon d o n .
Anonymo u s ( 1 9 7 5a ) . Ame ndme n t s to t he export g ra d i ng s y stem . T h e New Zea l a n d Meat Prod u c e r 3 : ( 4 ) 8- 1 0 .