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Climatic Factors Affecting Red Meat Production by E.J. Warwick*
INTRODUCTION
T h i s p a p e r i s i n t e n d e d to be an o v e r a l l s u m m a r y of known c l i m a t i c e f f e c t s on r e d m e a t p r o d u c t i o n . G e n e r a l r e c o m m e n d a t i o n s f o r a l l e v i a t i n g d e t r i m e n t a l e f f e c t s a r e g i v e n . R e f e r e n c e s c i t e d in t h e t e x t and l i s t e d in the ' L i t e r a t u r e Cited' s e c t i o n a r e m o s t l y r e v i e w s o r r e c e n t r e s e a r c h p u b l i c a t i o n s . T h e y a r e not i n t e n d e d to be e x h a u s t i v e but w i l l p r o v i d e e n t r 6 e to t h e v o l u m i n o u s s c i e n t i f i c l i t e r a t u r e d i r e c t l y o r i n d i r e c t l y r e l a t e d to t h e s u b j e c t of the p a p e r . A w i d e v a r i e t y of t o p i c s r e l e v a n t to t h e p r e s e n t p a p e r w e r e c o v e r e d in the r e c e n t P r o c . of t h e I n t e r n a t i o n a l L i v e s t o c k E n v i r o n m e n t a l S y m p o s i u m (A. S . A . E . , 1974). The r e a d e r is r e f e r r e d to t h i s p u b l i c a t i o n in i t s e n t i r e t y a s w e l l a s to s p e c i f i c r e v i e w s and r e p o r t s i n c l u d e d in it, s o m e of w h i c h a r e i n d i v i d u a l l y c i t e d s u b s e q u e n t l y . O t h e r r e l e v a n t r e v i e w s and r e s e a r c h r e p o r t s of a b r o a d n a t u r e i n c l u d e B i a n c a (1965), Bond (1967), Bond et a l . (1958), F . A . O . (1968), Hafez (1959), J o h n s o n (1967), McDowell (1972), P h i l l i p s (1958), Shaw (1967), U l b e r g (1958 and 1967), W a r w i c k (1958), W a r w i c k and Bond (1966), and W i l l i a m s o n and P a y n e (1959). C l i m a t i c v a r i a t i o n s affect r e d m e a t p r o d u c t i o n in m a n y w a y s . Some c l i m a t i c e f f e c t s a r e t h e r e s u l t of d i r e c t a c t i o n upon t h e a n i m a l w h e r e a s o t h e r s a r e r e s u l t s of i n d i r e c t e f f e c t s and a r e r e l a t e d to t y p e s and q u a n t i t i e s of feed w h i c h can be grown on s p e c i f i c a r e a s of land, life c y c l e s of i n t e r n a l and e x t e r n a l p a r a s i t e s , and s u r v i v a l of d i s e a s e o r g a n i s m s . INDIRE
CT E FFE CTS
A m o n g c l i m a t i c v a r i a b l e s , p r e c i p i t a t i o n is of p r i m a r y i m p o r t a n c e . Both t o t a l p r e c i p i t a t i o n and i t s d i s t r i b u t i o n have p r o f o u n d e f f e c t s upon both t h e a m o u n t s and n u t r i t i o n a l v a l u e s of f e e d s p r o d u c e d . T e m p e r a t u r e , d a y length, s e a s o n a l t e m p e r a t u r e v a r i a t i o n and s o i l f e r t i l i t y l i k e w i s e have t r e m e n d o u s i n f l u e n c e s upon the a m o u n t s and q u a l i t y of f o r a g e and o t h e r f e e d s p r o d u c e d . Soil f e r t i l i t y i s l o g i c a l l y i n c l u d e d in t h i s g r o u p i n g s i n c e m a n y s o i l c h a r a c t e r i s t i c s a r e i n f l u e n c e d by c l i m a t e . See McDowell (1972, C h a p t e r 6) and W i l l i a m s o n and P a y n e (1958, C h a p t e r 3) f o r d i s c u s s i o n s of f o r a g e q u a l i t y in the t r o p i c s . F o r a g e q u a l i t y i s a p a r t i c u l a r p r o b l e m in t r o p i c a l and s u b t r o p i c a l a r e a s . T y p i c a l l y , t r o p i c a l g r a s s e s a r e high in f i b e r and lignin and low in s o l u b l e c a r b o h y d r a t e s (Johnson and Pezo, 1975). Often t h e y a r e v e r y low in d i g e s t i b l e p r o t e i n , e s p e c i a l l y at m a t u r i t y o r a f t e r l e a c h i n g . L i k e w i s e , m i n e r a l content i s often a p r o b l e m . In m a n y t r o p i c a l and s u b t r o p i c a l e n v i r o n m e n t s , e i t h e r t h e r e a r e no a d a p t e d l e g u m e s o r t h e l e g u m e s t h a t c a n be g r o w n have c h a r a c t e r i s t i c s t h a t l i m i t t h e i r u s e f u l n e s s to l i v e s t o c k . Another important indirect Generally speaking, parasite of t h e w o r l d than e l s e w h e r e . t h o s e t r a n s m i t t e d by i n s e c t s
effeet of c l i m a t e r e l a t e s to life c y c l e s of i n t e r n a l and e x t e r n a l p a r a s i t e s . p r o b l e m s a r e m o r e i m p o r t a n t in h u m i d t r o p i c a l and s u b t r o p i c a l a r e a s S i m i l a r g e n e r a l i z a t i o n s can be m a d e about c e r t a i n d i s e a s e s , e s p e c i a l l y ( W i l l i a m s o n and Payne, 1959).
In view of t h e n a t u r e and m a g n i t u d e of i n d i r e c t c l i m a t i c e f f e c t s , t h e y a r e p r o b a b l y by f a r t h e m o s t i m p o r t a n t of all c o n s t r a i n t s upon t h e w o r l d ' s r e d m e a t p r o d u c t i o n .
*) U . S . Dept of A g r i c u l t u r e , A g r i c u l t u r a l R e s e a r c h S e r v i c e , B e i t s v i l l e , Md 20705, USA.
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DIRECT E F F E C T S D i r e c t e f f e c t s of c l i m a t i c v a r i a b l e s on a n i m a l s a r e of m a j o r i m p o r t a n c e . Low t e m p e r a t u r e s often s e r i o u s l y l i m i t a n i m a l p r o d u c t i o n . Chiliing is a m a j o r c a u s e of d e a t h l o s s e s in n e w b o r n a n i m a l s ( W i l l i a m s , 1967). When o l d e r l i v e s t o c k a r e e x p o s e d to e x t r e m e l y low t e m p e r a t u r e s , d e a t h l o s s e s m a y a l s o be high. We a r e a l l f a m i l i a r with the fact that u n d e r b l i z z a r d c o n d i t i o n s in t h e G r e a t P l a i n s of the United S t a t e s and e l s e w h e r e in the w o r l d , l o s s e s a r e o c c a s i o n a l l y c a t a s t r o p h i c . L e s s f a m i l i a r i s t h e f a c t that even in s u b t r o p i c a r e a s , h e a v y d e a t h l o s s e s m a y r e s u l t f r o m c o l d s h o c k . I w e l l r e m e m b e r t r a v e l i n g the length of the State of F l o r i d a in F e b r u a r y 1951 and o b s e r v i n g t h o u s a n d s of c a r c a s s e s of d e a d beef c a t t l e . In t h i s p a r t i c u l a r c a s e , the l o s s e s w e r e due to a p e r s i s t e n t c o l d r a i n a f t e r a p e r i o d of u n s e a s o n a b l y w a r m w e a t h e r . Many of the c a t t l e t h a t d i e d had been u n d e r n o u r i s h e d , but even in s o m e r e a s o n a b l y w e l t n o u r i s h e d h e r d s , l o s s e s w e r e s u b s t a n t i a i . Not only do low t e m p e r a t u r e s c a u s e t h e s e d r a m a t i c l o s s e s , bt~t they a l s o r e d u c e t h e e f f i c i e n c y of a n i m a l p e r f o r m a n c e in at l e a s t two o t h e r w a y s . F i r s t , when t h e a n i m a l is m a i n t a i n e d u n d e r c o n d i t i o n s c o l d enough to r e q u i r e t h e u s e of food e n e r g y to m a i n t a i n n o r m a l body t e m p e r a t u r e s , l e s s e n e r g y is a v a i l a b l e for p r o d u c t i o n , and g r o s s e f f i c i e n c y of p r o d u c t i o n s u f f e r s . The c r i t i c a l 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 below w h i c h f e e d e n e r g y m u s t be u s e d f o r body t e m p e r a t u r e m a i n t e n a n c e v a r y g r e a t l y with s p e c i e s , age, l e v e l of feeding, and t y p e of c o a t . E f f e c t s of low t e m p e r a t u r e s a r e g r e a t l y a c c e n t u a t e d by wind ( A m e s , 1974; A m e s and Insley, 1975) and r a i n . In s e v e r e c a s e s a n i m a l s m a y have to b r e a k down body t i s s u e s a s a s o u r c e of e n e r g y f o r t e m p e r a t u r e m a i n t e n a n c e . B l a x t e r (1965) c o n c i s e l y c o v e r s a w i d e r a n g e of b a s i c and a p p l i e d a s p e c t s of t h e s e problems. Second, u n d e r at l e a s t c e r t a i n c o n d i t i o n s of p r o l o n g e d e x p o s u r e to low 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 r a t i o n d i g e s t i b i l i t y is s u b s t a n t i a l l y r e d u c e d ( C h r i s t o p h e r s o n , 1975; W e s t r a and C h r i s t o p h e r s o n , 1975; Young and C h r i s t o p h e r s o n , 1974). O v e r a l l e f f e c t s of low t e m p e r a t u r e s on e f f i c i e n c y of p r o d u c t i o n can be l a r g e . M i I l i g a n and C h r i s t i son (1974) in a 7 - y e a r s t u d y of 1,970 s t e e r s fed at Saskatoon, S a s k a t c h e w a n , w i t h bedding and s h e l t e r f r o m wind, found t h a t a v e r a g e d a i l y g a i n s in D e c e m b e r , J a n u a r y and F e b r u a r y w e r e only 70% a s high as g a i n s d u r i n g the r e s t of t h e y e a r and t h a t 220 kg of a d d i t i o n a l f e e d w a s r e q u i r e d to r e a c h s l a u g h t e r weight f o r s t e e r s fed d u r i n g t h i s p e r i o d . R e c e n t r e s e a r c h ( H o l m e s and M c l e a n , 1974; M y r e s and Bowland, 1973; and V e r s t e g e n and Van d e r Hel, 1974) h a s e x t e n d e d knowledge of t e m p e r a t u r e e f f e c t s on swine u n d e r d i f f e r e n t h o u s i n g s i t u a t i o n s . The e f f e c t s of high t e m p e r a t u r e s upon a n i m a l p e r f o r m a n c e have been the s u b j e c t of a g r e a t d e a l of r e s e a r c h . H e r e t h e b a s i c p r o b l e m is k e e p i n g body t e m p e r a t u r e s f r o m e x c e e d i n g n o r m a l l e v e l s . In o r d e r to o v e r c o m e t h i s b a s i c p r o b l e m , a n i m a l s r e d u c e f e e d i n t a k e . The r e d u c e d f e e d i n t a k e r e d u c e s the a m o u n t of m e t a b o l i c heat p r o d u c e d and thus a i d s in the m a i n t e n a n c e of n o r m a l body t e m p e r a t u r e . W h e n e v e r a n i m a l s r e d u c e feed intake, t h e i r p e r f o r m a n c e is r e d u c e d (McDowell, 1972, C h a p t e r s 3 and 4). R e d u c e d f e e d i n t a k e is only one of the a d v e r s e effects of high t e m p e r a t u r e s . Other a d v e r s e e f f e c t s i n c l u d e i n t e r f e r e n c e with n o r m a l e s t r u a l c y c l e s , r e d u c t i o n s in s p e r m p r o d u c t i o n and q u a l i t y , r e duced v i a b i l i t y of n e w l y f e r t i l i z e d ova, and, in e x t r e m e c o n d i t i o n s , t e r m i n a t i o n of e s t a b l i s h e d p r e g n a n c i e s {Gwazdaushas et a l . , 1975; I n g r a h a m , 1974; I n g r a h a m et a l . , 1974; R o l l e r and S t o m baugh, 1974; and Stott, 1974). The e f f e c t s of both high and low t e m p e r a t u r e s upon l i v e s t o c k a r e i n t e n s i f i e d at h i g h e r h u m i d i t y l e v e l s (McDowell, 1974, p p . 3 0 - 3 2 ) . A L L E V I A T I O N OF U N F A V O R A B L E C L I M A T I C E F F E C T S F o r r u m i n a n t production, an e s s e n t i a l a p p r o a c h is to t a k e m e a s u r e s t h a t w i l l i n c r e a s e t h e y i e l d and q u a l i t y of f o r a g e s . In a r e a s of low p r e c i p i t a t i o n , d r o u g h t - t o l e r a n t p l a n t s p e c i e s c a n be grown, s t o c k i n g r a t e s can be a d j u s t e d to l e v e l s c o m p a t i b l e w i t h s u s t a i n e d c a r r y i n g c a p a c i t y on r a n g e s and o t h e r g r a z i n g land, and i r r i g a t i o n w a t e r c a n be u s e d j u d i c i o u s l y . Use of d r o u g h t - t o l e r a n t p l a n t s is a l o c a t i o n - s p e c i f i c p r o b l e m . No r e c o m m e n d a t i o n s can be m a d e o t h e r than upon t h e b a s i s of s p e c i f i c r e s e a r c h a d a p t e d to a given l o c a t i o n . Stocking r a t e s a r e i m p o r t a n t w o r l d w i d e . A l m o s t i n v a r i a b l y we find that g r a z i n g a r e a s u s e d upon a ' c o m m o n s ' b a s i s a r e o v e r s t o c k e d . O v e r s t o c k i n g has been h i s t o r i c a l l y i m p o r t a n t and is thought to have been a m a j o r f a c t o r in d e s e r t i f i c a t i o n of l a r g e a r e a s of the e a r t h ' s s u r f a c e . It r e s u l t s in keeping a n i m a l s at o r n e a r m a i n t e n a n c e n u t r i t i o n a l l e v e l s w i t h
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r e s u l t a n t Low outputs of m e a t and m i l k p e r unit of feed n u t r i e n t s consumed. Unfortunately, o v e r stocking is continuing in many a r e a s and is c u r r e n t l y a p r o b l e m of m a j o r p r o p o r t i o n s , p a r t i c u l a r l y in the Middle E a s t ( F . A . O . , 1972). Use of f e r t i l i z e r s can have m a j o r effects on total yield of f o r a g e . Rational f e r t i l i z e r use must r e s t upon r e s e a r c h c a r r i e d out under conditions of specific locations to d e t e r m i n e r e s p o n s e s and to equate them with cost. With the r e c e n t w o r l d - w i d e i n c r e a s e s in f e r t i l i z e r p r i c e s , making g e n e r a l r e c o m m e n d a t i o n s is much m o r e difficult now than it would have been a few y e a r s ago. A n u m b e r of steps can be taken to i m p r o v e f o r a g e quality and t h e r e b y i n c r e a s e animal p e r f o r m a n c e . The f i r s t and m o s t obvious approach is to take advantage of genetic v a r i a t i o n . Selection of t y p e s to be grown in a specific a r e a should be on both i n t e r - and i n t r a s p e c i e s b a s e s . Selection of types within s p e c i e s which have the g r e a t e s t potential for production of high quality forage is an a r e a of r e s e a r c h that has begun to b e a r fruit only within c o m p a r a t i v e l y r e c e n t y e a r s . The outstanding example of a new f o r a g e s e l e c t e d s p e c i f i c a l l y for its ability to i m p r o v e animal p e r f o r m a n c e is C o a s t c r o s s - 1 b e r m u d a g r a s s (Burton, 1972; Burton et a l . , 1967; Utley et a l . , 1974). A l a r g e number of b e r m u d a g r a s s s e l e c t i o n s and hybrids w e r e s c r e e n e d for f o r a g e d i g e s t i b i l i t y using the in vivo nylon bag technique. A hybrid identified as outstanding was designated C o a s t c r o s s - 1 . Subsequent animal evaluation d e m o n s t r a t e d s u p e r i o r p e r f o r m a n c e when it was fed as e i t h e r hay and p a s t u r e . I b e l i e v e plant b r e e d e r s have not yet explored the full range of p o s s i b i l i t i e s of breeding s p e c i f i c a l l y for nutritional value. C e r t a i n l y it is one of the m o s t intriguing a r e a s for future effort. F e r t i l i z a t i o n , in addition to i n c r e a s i n g yield, also is a m a j o r d e t e r m i n a n t of forage quality. In many a r e a s of the w o r l d i n c r e a s e d attention should be given to h a r v e s t i n g and p r e s e r v i n g f o r a g e s at s t a g e s of m a x i m u m nutritional value before the quality has d e t e r i o r a t e d as a r e s u l t of m a t u r i t y , d o r m a n c y or leaching. A second m a j o r p o s s i b i l i t y for i n c r e a s i n g efficiency of r e d m e a t production is control of p a r a s i t e s and d i s e a s e s . Reduction of l o s s e s due to internal and e x t e r n a l p a r a s i t e s and to d i s e a s e s depends upon (1) the diagnosis of the situation, (2) the development of management s y s t e m s for m i n i m i z i n g l o s s e s and (3) the use of a p p r o p r i a t e t h e r a p e u t i c t r e a t m e n t s . Reducing s t r e s s on a n i m a l s is a t h i r d a r e a of m a j o r i m p o r t a n c e in i m p r o v i n g animal production under unfavorable c l i m a t i c situations. Means a v a i l a b l e for this a r e many and v a r i e d , and p o s s i b i l i t i e s a r e often l i m i t e d only by the ingenuity of the r e s e a r c h e r or livestock p r o d u c e r . Many effective p r o c e d u r e s have t h e i r origins in antiquity. A p r i m e example is m i g r a t o r y l i v e s t o c k production s y s t e m s in which a n i m a l s a r e p a s t u r e d at lower elevations during the cool s e a s o n s of the y e a r and at higher elevations during the s u m m e r months. Someone has said that t h e s e s y s t e m s a r e n e a r l y ideal because in some a r e a s both l i v e s t o c k and h e r d e r s a r e able to live at 22°C the y e a r round! Moving l i v e s t o c k with s e a s o n a l w e a t h e r changes is only one p o s s i b i l i t y of adapting livestock production to existing conditions. A m y r i a d of other p o s s i b i l i t i e s include avoiding e i t h e r mating or b i r t h of young during s e a s o n s of unfavorabie weather, avoiding the fattening of a n i m a l s on high e n e r g y r a t i o n s during the hotter months of the y e a r , and using n a t u r a l bodies of w a t e r for cooling a n i m a l s during e x t r e m e s u m m e r heat, to cite a few e x a m p l e s . F o r the c o m m e r c i a l l i v e s t o c k p r o d u c e r , the question is often one of providing s h e l t e r or some other means of t e m p e r a t u r e control, or both. P o s s i b i l i t i e s range f r o m the v e r y s i m p l e to the most sophisticated. Much r e s e a r c h has shown that for reducing s t r e s s due to high t e m p e r a t u r e s , anything that tends to effect reductions of even a few d e g r e e s will l i k e l y benefit animal production. P e r h a p s the most thoroughly studied example is the feedlot situation in the I m p e r i a l Valley of C a l i f o r n i a in which r e s e a r c h has shown that the u s e of shades, the use of cable or pipe fences r a t h e r than planks to p r o m o t e a i r movement and r e d u c e r a d i a n t heat loads, and the use of cooled drinking w a t e r , evap o r a t i v e c o o l e r s , s p r a y s to promote cooling through evaporation, and m e c h a n i c a l a i r conditioning all w e r e effective in i m p r o v i n g animal p e r f o r m a n c e , e s p e c i a l l y with a n i m a l s of European b r e e d s (Ittner et a l . , 1958; M o r r i s o n et a l . , 1973). Much information is also a v a i l a b l e on protection of swine f r o m e x t r e m e s of high t e m p e r a t u r e s and the effects on production of deviations f r o m optimum (Bond, 1974). S i m i l a r l y , for protection of c a t t l e f r o m e x t r e m e s of cold, the use of windbreaks, o p e n - f r o n t e d sheds, c l o s e d buildings, and c l o s e d buildings with heat, all a r e effective in reducing t e m p e r a t u r e s t r e s s upon the animal (Hegg et a l . , 1974; MeDowell, 1974; Pontif et a l . , 1974; Self and Hoffman, 1974; W i l l i a m s , 1967). Natural windbreaks, taking advantage of topography or t r e e growth, can be v e r y useful when a v a i l a b l e .
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When the s u i t a b i l i t y of a p a r t i c u l a r s t r u c t u r e o r p r o c e d u r e is being studied, t h e b a s i c c o n s i d e r a t i o n m u s t i n c l u d e biology, e n g i n e e r i n g and e c o n o m i c s . To m a k e r a t i o n a l c h o i c e s , t h e p r o d u c e r m u s t have a v a i l a b l e (1) knowledge of p r o b a b l e d e l e t e r i o u s e f f e c t s of the p a r t i c u l a r s t r e s s o r s t r e s s e s upon his a n i m a l s if not c o n t r o l l e d , (2) e n g i n e e r i n g a b i l i t y to r e d u c e o r e l i m i n a t e s t r e s s e s at m i n i m u m c o s t s , and (3) e c o n o m i c s k i l l s to equate p o t e n t i a l l o s s e s with the c o s t of a l l e v i a t i o n . G e n e r a l r u l e s can s c a r c e l y be given. In r e c e n t y e a r s r e s e a r c h a t t e n t i o n has been given to t h i s p r o b l e m (Hahn, 1974; O s b u r n and Hahn, 1968 and 1974). S e v e r a l m a t h e m a t i c a l a p p r o a c h e s have been d e v e l o p ed f o r c h a r a c t e r i z i n g and m o d e l i n g t h e r m a l r e l a t i o n s in m e a t a n i m a l s , t h e i r r e q u i r e m e n t s f o r s h e l t e r and p r e d i c t e d p e r f o r m a n c e at given 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 ( B u t c h b a k e r et a l . , 1973; P a i n e and B u t c h b a k e r , 1971; P a i n e et a l . , 1974; P e t r i t z and B r o k k e n , 1974; T e t e r et a l . , 1973). R e g a r d l e s s of m e t h o d s u s e d , d e t e r m i n a t i o n s m u s t be b a s e d upon e ~ r e f u l s t u d y and knowledge of e a c h i n d i v i d u a l s i t u a t i o n . Some s i t u a t i o n s have been w e l l r e s e a r c h e d w h e r e a s o t h e r s a r e s t i l l d e p e n d e n t upon a d d i t i o n a l knowledge. I a m t h i n k i n g p a r t i c u l a r l y h e r e of q u e s t i o n s such as "how m u c h c a n be i n v e s t e d in s h e l t e r f o r r a n g e c a t t l e to g u a r d a g a i n s t t h e o c c a s i o n a l c a t a s t r o p h i c l o s s t h a t m a y o c c u r only once in m a n y y e a r s ? " T a k i n g a d v a n t a g e o f g e n e t i c v a r i a t i o n in a n i m a l s i s a f o u r t h a p p r o a c h to i m p r o v i n g a n i m a l p r o d u c t i o n u n d e r c o n d i t i o n s of c l i m a t i c s t r e s s . D i f f e r e n t s p e c i e s w e r e d o m e s t i c a t e d and a r e now r e a r e d in d i f f e r e n t p a r t s of t h e w o r l d . P a t t e r n s of d o m e s t i c a t i o n i n d i c a t e that, c o n s c i o u s l y o r unc o n s c i o u s l y , m a n has been u t i l i z i n g g e n e t i c v a r i a b i l i t y f o r t h i s p u r p o s e f r o m the beginning of r e c o r d e d h i s t o r y . F u r t h e r , u n d e r p r i m i t i v e c o n d i t i o n s , m o s t l i v e s t o c k h e r d s and f l o c k s p r o b a b l y w e r e kept in a s i n g l e l o c a t i o n o r in m o r e o r l e s s c o n s t a n t m i g r a t o r y p a t t e r n s . U n d e r t h e s e c o n d i t i o n s , t h e r e w a s w i t h i n - s p e c i e s n a t u r a l s e l e c t i o n f o r t y p e s with a b i l i t y to s u r v i v e and r e p r o d u c e in t h e e n v i r o n m e n t s c h a r a c t e r i s t i c of t h e i r m a n - m a d e h a b i t a t s and with w h a t e v e r i n t e n t i o n a l s e l e c t i o n m a n m a y have u s e d . Only when m o d e r n m a n began d e m a n d i n g that a n i m a l s o c c u p y e c o l o g i c a l n i c h e s for w h i c h t h e y w e r e not d e s i g n e d did g e n e t i c a d a p t a t i o n to s p e c i f i c e n v i r o n m e n t s b e c o m e a r e a l p r o b l e m . M a n ' s f u r t h e r d e m a n d s that a n i m a l s p r o d u c e at l e v e l s f a r g r e a t e r than e v e r a t t a i n e d in n a t u r e o r in p r i m i t i v e c i r c u m s t a n c e s have a c c e n t u a t e d the p r o b l e m . The n a t u r e and m a g n i t u d e of g e n e t i c d i f f e r e n c e s in a d a p t a b i l i t y to s p e c i f i c e n v i r o n m e n t s a r e i n c o m p l e t e l y u n d e r s t o o d . Thus, g e n e r a l r e c o m m e n d a t i o n s cannot be m a d e at t h i s t i m e (McDowell, 1972, C h a p t e r 5). Many r e s e a r c h e r s have c o m p a r e d p h y s i o l o g i c a l and p r o d u c t i o n r e s p o n s e s of Zebu ( Bos ir~li~ ) with E u r o p e a n b r e e d s (B0s taur~) of c a t t l e at high 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 . Z e b u t y p e s have a g r e a t e r a b i l i t y to m a i n t a i n n o r m a l body t e m p e r a t u r e s . This a b i l i t y i s r e l a t e d to l o w e r m e t a b o l i c h e a t p r o d u c t i o n and l o w e r d i g e s t i v e c a p a c i t y t h a t p r o b a b l y l i m i t s t h e a p p e t i t e . In s o m e s i t u a t i o n s , Z e b u t y p e s a r e m o r e p r o d u c t i v e than E u r o p e a n b r e e d s ; but, g e n e r a l l y s p e a k i n g , d i f f e r e n c e s s e e m to be m o r e highly r e l a t e d to s u r v i v a l a b i l i t y than to high p r o d u c t i o n l e v e l s . Z e b u - E u r o p e a n c r o s s b r e d s have u s u a l l y e x h i b i t e d a g r e a t d e a l of h e t e r o s i s and often e x c e e d p r o d u c t i v i t y of e i t h e r p a r e n t a l t y p e by wide m a r g i n s (Koger, et a l . , 1975; K o g e r et a l . , 1973). In s o m e h i g h - t e m p e r a t u r e s i t u a t i o n s , r a t e and e f f i c i e n c y of gain of Z e b u - E u r o p e a n c r o s s b r e d t y p e s have not been i m p r o v e d by c o o l e d d r i n k i n g w a t e r o r o t h e r p r o c e d u r e s to a s g r e a t an e x t e n t a s i s t r u e of E u r o p e a n b r e e d s ( L o f g r e e n et a l . , 1975; M o r r i s o n et a l . , 1974). A p p a r e n t d i f f e r e n c e s in a d a p t a t i o n of d i f f e r e n t s t r a i n s of beef c a t t l e of a E u r o p e a n b r e e d to a s u b t r o p i c e n v i r o n m e n t have been o b s e r v e d (Butts et a l . , 1971). P r e s e n t l y , t h e i m p o r t a n c e of w i t h i n b r e e d d i f f e r e n c e s in a d a p t a t i o n to s p e c i f i c e n v i r o n m e n t s is not w e l l u n d e r s t o o d . Sheep b r e e d s i n d i g e n o u s to w a r m c l i m a t e s have c h a r a c t e r i s t i c s thought to be a d a p t i v e (McDowell, 1972), but s h e e p have not been s t u d i e d a s e x t e n s i v e l y a s c a t t l e . Meat a n i m a l p r o d u c e r s should m a k e e v e r y e f f o r t to t~tilize e x i s t i n g knowledge c o n c e r n i n g t h e p r o d u c t i o n p o t e n t i a l of d i f f e r e n t g e n e t i c t y p e s in t h e i r p a r t i c u l a r e n v i r o n m e n t a l s i t u a t i o n s in d e t e r m i n i n g t y p e s to u s e in e i t h e r s t r a i g h t b r e e d i n g o r c r o s s b r e e d i n g p r o g r a m s . Much k n o w l e d g e of t h i s kind i s a v a i l a b l e f o r m a n y a r e a s of t h e w o r l d , but t h e r e a r e o t h e r a r e a s w h e r e k n o w l e d g e i s v e r y l i m i t e d . Undoubtedly, t h e c o m p l e t e r a n g e of g e n e t i c v a r i a t i o n p o t e n t i a l l y a v a i l a b l e to l i v e s t o c k p r o d u c e r s has been s t u d i e d v e r y , v e r y s u p e r f i c i a l l y . However, enough i n f o r m a t i o n i s a v a i l a b l e to i n d i c a t e that p o t e n t i a l s a r e e n o r m o u s . O p p o r t u n i t i e s e x i s t both f o r s e l e c t i n g b e t w e e n s p e c i e s and u t i l i z i n g g e n e t i c v a r i a b i l i t y as it o c c u r s within s p e c i e s . Once a t y p e o r c r o s s h a s been s e l e c t e d f o r c o m m e r c i a l p r o d u c t i o n in a g i v e n a r e a , s t u d f l o c k s o r h e r d s f o r t h e p r o d u c t i o n of b r e e d i n g m a l e s should be m a i n t a i n e d in t h e s a m e e n v i r o n m e n t .
190 SUMMARY
Environmental d i f f e r e n c e s due to c l i m a t i c f a c t o r s have profound d i r e c t and i n d i r e c t effects on efficiency of r e d m e a t production. Alleviation of unfavorable effects depends on understanding them and applying a p p r o p r i a t e c o r r e c t i v e action. Depending upon the n a t u r e of the c l i m a t i c s t r e s s , actions to be taken m a y include : (1) i m p r o v i n g quantities of a v a i l a b l e feed by management p r o c e d u r e s such as control of g r a z i n g intensity, (2) i m p r o v i n g quality of feedstufts by using a p p r o p r i a t e genetic types of crop plants and other techniques, (3) controlling p a r a s i t e s and d i s e a s e s , (4) p h y s i c a l l y changing the environment through p r o v i s i o n of s h e l t e r or by other a p p r o a c h e s as e c o n o m i c a l l y justified, and (5) using genetic types of l i v e s t o c k best adapted to specific situations. REFERENCES
AMES, D.R. (1974)
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