I22 BODY SIZE AND PRODUCTION EFFICIENCY* EARLE W. KLOSTERMAN Ohio A g r i c u l t u r a l Research and Development Center Wooster, Ohio Beef c a t t l e s e l e c t i o n and performance t e s t i n g procedures i n recent years placed much emphasis upon rate of gain. In a search f o r f a s t gaining animals, numerous new breeds of l a r g e r type have been i n t r o duced and s e l e c t i o n f o r gain has increased mature s i z e i n a number of herds of e x i s t i n g breeds. The National Association of Animal Breeders has i d e n t i f i e d 68 breeds of c a t t l e in t h i s country. A tremendous v a r i a t i o n i n type of c a t t l e i s now a v a i l a b l e t o t h e beef producer. This v a r i a t i o n has led t o many questions. How b i g should c a t t l e be, how f a s t should they gain, what i s t h e r e l a t i o n s h i p between rate of gain and feed efficiency, how much milk should they give, w h a t carcass w e i g h t and grade is most d e s i r a b l e, a r e t h e r e i n t e r a c t i o n s among types of c a t t l e and a v a i l a b l e feed supplies, e t c. A number of experiments have been conducted a t The Ohio A g r i c u l t u r a l Research and Development Center t o obtain information on t h e s e questions. Results of t h e s e experiments have been prepared f o r publication by Klosterman and Parker (1976)~. Detailed d a t a obtained in t h e s e experiments w i l l not be repeated here b u t only t h e conclusions which appear justified. b intenance Energy requirement f o r maintenance is a tremendous overhead which t h e beef industry must c a r r y. Do c a t t l e d i f f e r i n t h e i r requirements f o r maintenance? If so, t h i s v a r i a t i o n does not appear t o be g e n e t i c. Per u n i t of metabolic w e i g h t (W0*75), Hereford and Charolais cows did not d i f f e r s i g n i f i c a n t l y i n amount of feed required t o maintain constant weight. However, f a t cows required l e s s feed per u n i t of w e i g h t than t h i s cows. A beef cow v a r i e s widely i n weight depending upon her condition, a v a r i a t i o n which may be g r e a t e r than t h e a c t u a l v a r i a t i o n i n maintenance needs of t h a t individual. If, f o r example, a 1,000 pound cow i s f a t t e n e d t o 1,200 pounds and then fed as a 1,200 pound * Presented a t t h e 29th Annual Reciprocal Meat Conference of t h e American Meat Science Association, 1976. Klosterman, E. W. and C. F. Parker 1976. Effect of s i z e, breed, and sex upon feed e f f i c i e n c y i n beef c a t t l e. Ohio A g r i c u l t u r a l Research and Development Center, Research B u l l e t i n, ( i n press ).
cow she is l i k e l y t o continue t o gain weight. If, however, she i s starved t o 800 pounds and then a s a 800 pound animal, she i s l i k e l y t o continue t o l o s e weight. Does t h e so-called "easy-keeping" cow have a slower mintenance requirement or does she e a t more than her share of feed? I suspect t h e l a t t e r may be t r u e. Cow Size An experiment was conducted a t OARDC t o measure t h e t o t a l feed e f f i c i e n c y of beef cows of d i f f e r e n t s i z e s and breeds. Individual feed consumption records of cows f o r a f u l l year and t h e i r calves t o choice slaughter condition were obtained during a 4 year period f o r 133 cowc a l f pairs. Milk production of t h e cows and weights, gains and carcass d a t a of t h e i r calves were recorded. These included Hereford, T e r e f o r d x A n g u s, Hereford x Charolais, and Charolais cows varying in s i z e. One h a l f of t h e cows of each breed were bred t o Hereford b u l l s and t h e other half t o C h a r o l a i s b u l l s. The r e s u l t s obtained were studied according t o t h r e e weight c l a s s e s with t h e e f f e c t s of breed removed and according t o breed with e f f e c t s of weight c l a s s removed. Some cows of a l l breeds were included i n each of t h e weight c l a s s e s which averaged 874, 1022 and 1210 pounds. The heavier cows had g r e a t e r weight-to-height r a t i o s (a measure of condition) and weaned s i g n i f i c a n t l y heavier calves. They required more t o t a l feed and t h e i r calves a t e more feed p r i o r t o weaning. The differences among weight c l a s s e s i n t o t a l d i g e s t i b l e n u t r i e n t s (TDN) required per pound of weaning weight were small. Differences in post -weaning performance were not s i g n i f i c a n t amng weight c l a s s e s, b u t calves from t h e l a r g e r cows produced carcasses which were s i g n i f i c a n t l y heavier. Hereford x Angus cross cows produced t h e most milk weaned t h e heaviest calves and required t h e l e a s t TDN per pound of weaning w e i g h t. However, t h e i r calves were t h e least e f f i c i e n t on feed post-weaning. Differences in carcass t r a i t s amng calves out of t h e cow breeds were s i g n i f i c a n t a t t h e 5 percent l e v e l. Calves from t h e Hereford x Angus cross cows graded one-third grade higher than those from Charolais cows and were two weeks younger a t slaughter. Net e f f i c i e n c y ( t o t a l TDN consumed by t h e cow and c a l f divided by pounds of edible portion produced) tended t o be similar f o r a l l s i z e s and breeds of cows a s t h e r e were no s i g n i f i c a n t d i f f e r e n c e s among them in t h i s t r a i t. I r r e s p e c t i v e of condition as it a f f e c t s cow weight, c a l f production by cows of d i f f e r e n t s i z e s appears t o be in proportion t o t h e s i z e of t h e cow. Thus, s i z e of cow per s e seems t o be of minor importance i n c a l f production. I n t h e s e experiments, only 13 percent of t h e metabolizable energy fed t o t h e cow and c a l f was recovered as net energy i n t h e c a l f a t slaughter. Thus, 87 percent w a s required f o r m i n t e m n c e and other nonproductive functions. These d a t a include only' those c m - c a l f p a i r s which completed t h e experiment and hence are based on a 100 percent c a l f
124 crop slaughtered. Actual efficiency of production is somewhat lower than this and emphasizes the importance of culling non-productive cows from the herd. bturing Rate Rate of growth has been highly emphasized as an important production trait in beef cattle. However, the relationship between growth rate and efficiency of feed utilization among cattle of various types and sizes fed to similar carcass grade or degree of finish has not been significant. The important difference among individual cattle is not their rate of absolute gain but rather their rate of gain per unit of weight, relative gain. When fed to a constant grade, there is a highly significant relationship between relative gain and feed efficiency. Feedlot studies at OARDC and elsewhere have shown that earlier maturing types of cattle (small vs. large or heifers vs. bulls) eat more feed per unit of weight and finish at younger ages and lighter weights than later maturing types. The market generally prefers a certain degree of finish and discounts those cattle which are underfinished or over finished. Excessive finish can easily be avoided by slaughtering when the cattle are ready, however, under-finished cattle must be fed for longer periods of time. Hence, rate of mturing becomes an important trait in beef cattle. C. F. Parker at OARDC has derived a measure of maturing rate from an expression of relative gain as follows: which reduces to: 1 Age of slaughter This function measures rate of growth relative to the body weight at which time the desired degree of finish is attained. Feed consumption data obtained in the cow-size experiment, where calves were fed to a constant low choice grade, were used to correlate the term 1/Age at slaughter with feed efficiency. The correlation between this term and total TDN consumed by the cow and calf was -0.52, indicating that animsls with faster rates of maturity were more efficient. This relationship was highest with TDN required by the calf on feed following weaning (r = -0.63) and less (r = -0.22) with TDN required by the cow. This expression of maturing rate simply means that those cattle which produce the most carcass weight of the desired grade at the youngest age are the most efficient.
Energy Requirements for Gain NRC, Nutrient Requirements of Beef Cattle, indicate that heavier steers and heifers require more NE gain per unit of gain than lighter weight calves. These increases are generally considered to be due to changes in body composition and a question was raised if different sizes of cattle of different weights but with similar composition have different requirements. A three-year experiment was conducted to study this problem. Three groups, 212 head, of weanling heifer calves sired by Angus, Charolais, Jersey and Brown Swiss bulls out of Angus and Charolais dams were individually fed at either 1.5 or 2.0 times their maintenance energy requirement for 210 days. One-half of each breed type was fed each level of feed which was calculated from Woe75 and increased with individual weight gain each 14 days. As would be expected, average daily gain and energy per unit of gain were significantly different between the two levels of feeding in favor of the higher level. Although there were significant differences among breed types in initial weight and hence, in amounts of feed fed, there were no significant differences among them in absolute rate of gain. However, heifers with Angus breeding gained significantly faster per unit of metabolic size, relative gain, and required significantly less feed per unit of gain. There were no significant interact ions among breed types and levels of feeding in rate or efficiency of gain. These results indicate that larger type calves require more net energy per unit of absolute gain and that NRC requirements are accurate when applied to different breeds, crosses and sizes of cattle. Interactions Among Cattle and Feed Supplies Data on interactions which may exist among types of cattle of the same sex and types of diet are somewhat limited. However, differences among bulls, steers and heifers in rate of gain, feed intake per unit of weight, rate of maturing and carcass weight and composition are very similar to differences which exist among different sizes of cattle. If this analogy between sex and size may be mde and the two may be considered together, there appear to be definite interactions amng types of cattle and either types of diet or feeding systems. In a crossbreeding experiment, significant interactions between both breed (Hereford and Charolais) and sex (steers and heifers) and two systems of management were found. The two systems of management were: creep-feeding and finishing immediately following weaning vs. no creep-feeding, wintering, grazing for 60 days and finishing in dry lot. In combining the two sources of variation, breed and sex, it appeared that Charolais steers were best adapted to the early finishing system and Hereford heifers to the deferred system of management. It is well known that heifers finish more easily than steers and if bulls are to be finished at young ages they must be fed high energy rations.
126 It i s, t h e r e f o r e, apparent t h a t i f it i s most economical t o feed lower energy r a t i o n s, they w i l l be b e s t u t i l i z e d by e a r l y m t u r i n g types of c a t t l e which consume more feed per u n i t of weight and if high g r a i n r a t i o n s a r e t o be f e d, l a t e r maturing c a t t l e w i l l produce heavier, more d e s i r a b l e carcasses. If e a r l y maturing c a t t l e a r e f e d high grain r a t i o n s a t young ages, they must be slaughtered a t light weights or they w i l l become excessively f a t. Carcass Weight Supplies of f i n i s h e d, slaughter c a t t l e vary w i t h c a t t l e numbers and supplies of feed grains, however, a desired degree of f i n i s h i s generally preferred with both underf inished and overf inished c a t t l e s e l l i n g a t a discount. Much discussion has been given t o a most preferred slaughter weight, however, in t h e market, s i z e independent. of f i n i s h appears t o be of much l e s s importance than t h e desired degree of f i n i s h It i s my understanding t h a t t h e packer is a b l e t o r e a l i z e some n e t savings per pound of carcass beef handled by processing l a r g e r type c a t t l e. Although of r e a l e c o n a i c importance t o t h e packer, t h i s saving may be minor when r e l a t e d t o t o t a l c o s t s of beef production. There i s a l s o some demand, perhaps limited, f o r l i g h t e r weight, f i n i s h e d cattle. Experiments have been conducted w i t h c a t t l e of various breeds and s i z e s t o determine t h e i r energy requirements f o r maintenance, growth and f i n i s h i n g. Differences i n maintenance requirements of mature cows d i d not appear t o b e genetic b u t were influenced by condition. When t o t a l feed required by t h e cow f o r one year and her c a l f t o slaughter condition were measured i n pounds of edible beef produced per u n i t of energy consumed, t h e r e were no s i g n i f i c a n t differences among cows of d i f f e r e n t s i z e s o r breeds. When f e d t o a s i m i l a r degree of f i n i s h, t h e r e were no s i g n i f i c a n t d i f f e r e n c e s among s i z e s of c a t t l e i n feed required per u n i t of g a i n. There was a s i g n i f i c a n t r e l a t i o n s h i p between feed e f f i c i e n c y and r e l a t i v e gain, gain per u n i t of weight, but not between e f f i c i e n c y and absolute gain. It was concluded t h a t NRC energy requirements a r e accurate when applied t o d i f f e r e n t breeds, crosses and s i z e s of c a t t l e. Differences among types of c a t t l e were similar t o d i f f e r e n c e s among sexes. E a r l i e r maturing types were found t o consume more feed per u n i t of w e i g h t and t o f i n i s h a t younger ages and l i g h t e r weights. Heifers of small type appear b e s t s u i t e d t o deferred systems of management o r lower energy d i e t s and s t e e r s of l a r g e r type t o feeding high energy d i e t s a t young ages.
Traits which seem of importance for increasing energetic efficiency in beef cattle are feed intake or gain per unit of metabolic size and the ability to finish at a desirable carcass weight. Those cattle which will produce the most carcass weight of the desired grade at the youngest age will be the most efficient. This trait my be measured as the reciprocal of age at slaughter when carcass composition is constant. * * * Dave Anderson: To begin this session is another good friend, Dr. Bill Moody, Professor of Animal Science, University of Kentucky. Dr. Moody received his Doctorate at Missouri. He has done Postgraduate work at Wisconsin and most recently at the Research Institute in England. Today, Bill will be reviewing a most timely topic in which he will discuss the differences in the characteristics of beef from animals fed on different feeding regimes.