EXPERIMENTAL RESULTS ON CROSSBREEDING CATTLE FOR BEEF PRODUCTION ~ L. V. CUNDIFF :2

Transcription

1 S EXPERIMETAL RESULTS O CROSSBREEDIG CATTLE FOR BEEF PRODUCTIO ~ L. V. CUDIFF :2 U. S. Department o/ Agriculture ELECTIO and crossing of breeds are potential methods available to create genetic improvement. If non-additive and additive genetic variation are both important then improvement will be maximized by combining systematic crossbreeding with selection among and within breeds. In this manner, crossbreeding allows for utilization of heterosis and combining of desired characteristics in commercial cattle that would not be present in any parent breed alone. The purpose of this paper will be to review experimental results relating to choice of breeds. Considerable research has been conducted and much is in progress in the United States, primarily as a result of beef cattle breeding regional projects (W-l, XC-1 and S-10). The parameters of primary importance in choice of breeds are breeding values determined by average gene effects for the breeds and heterosis effects determined by interaction of gene effects and differences in average gene frequency between breeds (Willham, 16). The optinmm effect of crossbreeding would be realized by systematic crossing of breeds that excel in their breeding value for net merit and express maximum heterosis. Breeds can differ greatly in specific components of net merit and still be approximately equal overall. Crossing Herefords, Angus and Shorthorns These breeds of British origin, particularly Herefords and Angus are numerically the most prominent in America. For years they have been used for commercial production primarily as straightbreds. Breeding Value. Several experiments have provided information on the relative differences among these breeds. Herefords, Angus and Shorthorns have been involved in a heterosis experiment conducted by the Animal 1 Presented at the Beef Cattle Session of the 61st Annual Meeting of the American Society of Animal Science, Purdue University, August Beef Cattle Research Branch, Animal Husbandry Research Division, A.R.S., U.S.D.A., Lincoln, ebraska. 64 Husbandry Research Division, U.S.D.A. and the University of ebraska at Fort Robinson, ebraska (Gregory et al., 165; Gregory et al., 166a, b,c; Wiltbank et al., 166; Wiltbank et al., 167). The means for a number of performance traits based on breed of sire and breed of dam effects using both straightbred and crossbred data from these studies are presented in table 1. The heterosis experiment at Virginia has also involved Herefords, Angus and Shorthorns (Gaines et al., 166, 167; Vogt et al., 167). Results from these studies are summarized in the same manner as the Fort Robinson data in table 2. Differences among breeds for percent calf crop born and weaned have been small and not significant (Gaines et al., 166; Wiltbank et al., 167). Weaning weights were similiar for the three breeds in the Fort Robinson experiment (Gregory et al., 165). However, partitioning weaning weight into its two components, that due to the transmitted average gene effects upon the individual itself and that due to average gene effects upon the maternal environment, indicates that the superiority of Herefords in growth impulse over Angus and Shorthorns is offset by their below average maternal ability. Damon et al. (161) found that Herefords exceeded Angus in general combining ability for 180 day weight and that Angus exceeded Herefords in maternal abil- ity. The data reported by Gaines et al. (166) indicates that Herefords are deficient in maternal ability and slightly superior to Angus and Shorthorns in preweaning growth. Estimates of milk prodnction have been greater for Angus (Melton et al., 167; Schwulst et al., (168) and Shorthorn (Schwulst et al., 168) than for Herefords. Gregory et al. (166a, b) found that Hereford heifers gained more rapidly and steers more rapidly and efficiently postweaning than Angus or Shorthorns. Similiar results were observed for postweaning gain in Herefords and Angus by Damon et al. (161) and for postweaning gain and feed efficiency by Butler et al. (162) and Pahnish et al.

2 CROSSBREEDIG CATTLE TABLE 1. BREED EFFECTS FOR HEREFORDS, AGUS AD SHORTHORS I U.S.D.A. AD EBRASKA EXPERIMET AT FORT ROBI- SO (USIG ALL DATA--STRAIGHTBRED AD CROSSBRED) " Trait Hereford Angus Shorthorn Calves born, % Calves weaned, % Weaning weight, kg Individual effects, kg Maternal effects, kg --.0 q ~ 5.4 Postweaning--steers Daily gain, kg day, weight TD per unit gain from weaning to 400 kg Carcass grade b Retail product, % Fat trim, % Bone, % et merit,~ $ Postweaning--heifers a Daily gain, kg day weight, kg Age at puberty, days Weight at puberty, kg a Daily gain, kg day weight, kg Age at puberty, kg Weight at puberty, kg Mature weight, kg a Adapted from Gregory et al. (165; 166a, b c), Wiltbank et al. (166, 167) and L. V. Cundiff et al,' (unpublisked data). b ~high good, 10=low choice. e et merit is the value of the retail product minus feed costs from weaning to slaughter (452 days). dheifers born in 160 to 61 were fed a low level of energy associated with development to be bred as 2-year-olds. Heifers born in 162 to 63 were fed a moderate level of energy for development to be bred as yearlings. (16). In the Virginia experiment (Vogt et al., 167) postweaning gains were similiar for all three breeds. Angus and Shorthorns have exceeded Herefords in marbling and carcass grade (Damon et al., 160; Butler et al., 162; Gregory et al., 166c; Gaines et al., 167; Pahnish et al., 16). Detailed carcass cut-out of cattle in the Fort Robinson experiment (Gregory et al., 166c) revealed that Herefords and Angus contained more retail product and less fat trim than Shorthorns. When composition and efficiency of growth were combined into net merit computed as the value of retail product taking into account carcass grade and deducting feed costs from weaning to slaughter the Herefords exceeded the Angus and Shorthorns by 3.5% and 5.3%, respectively. The results reported by Damon et al. (160) also indicate that Herefords contain a higher percent lean and less fat than Angus or Shorthorns. Butler et al. (162) observed Herefords contained a FOR BEEF PRODUCTIO 65 higher percent of retail product in the round and loin than Angus, but a lower percent in the chuck. When heifers were fed and managed to be bred as yearlings the average age and weight at puberty was less for Shorthorns than Angus which in turn was less than that for Herefords (Wiltbank et al., 166). Age and weight at puberty were similiar for Angus and Shorthorns on the lower energy level associated with development to be bred as 2- year-olds and Angus and Shorthorns reached puberty at younger ages and lighter weights than Herefords. Recent analysis of weight and skeletal measurements taken on these females when they ranged from 6 to years of age indicates that Herefords are larger at maturity averaging 537 kg in mature weight compared to 46 kg and 48 kg in Angus and Shorthorns, respectively (L. V. Cundiff et al., unpublished data). All traits considered, including components of fertility, maternal ability, growth, efficiency of gain, carcass merit and mature size, it appears that the differences in total net merit may be relatively small. Crossing among these breeds will combine desired characteristics, but the major benefit of crossing British breeds is dependent on the degree of heterosis. Heterosis /or Individual Effects. Results on the effect of heterosis among British beef breeds from a number of experiments have been summarized by Mason (166) and Warwick (168). Table 3 presents the summary prepared by Warwick (168) for heterosis effects in first cross calves. TABLE 2. BREED EFFECTS FOR HEREFORDS, AGUS AD SHORTHORS I VIRGIIA EXPERIMET (USIG ALL DATA-- STRAIGHTBRED AD CROSSBRED) a Trait Hereford Angus Shorthorn Calves born, % Calves weaned, % Weaning weight, kg Individual effects, kg Maternal effects, kg Postweaning--steers Feedlot daily gain, kg Slaughter weight, kg Carcass grade b I. 5 Fat thickness, mm I. 3 Postweaning--heifers Feedlot daily gain Slaughter weight Carcass gradeb Fat thickness, ram a Adapted from Gaines et al (166), Vogt et al. (167) and Gaines et al. (167). b 10~-average good, ll~high good, 12~low choice.

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4 CROSSBREEDIG CATTLE FOR BEEF PRODUCTIO 67 Calving rate has been reported in six studies. Results favored crossbred matings in three. The weighted average advantage is 1.3%. Survival of crossbred calves has been higher in all six experiments in which it has been reported. The weighted average advantage is 3.0%. In five out of six experiments calf crop weaned has been greater for crossbred calves than for straightbred calves. Weaning weight of crossbred calves was superior to straightbreds in 12 of 13 experiments summarized by Warwick (168) with a weighted average advantage of 4.~. Postweaning growth, slaughter weight or yearling weight have been reported in experiments. Variations in age at final weight, feeding and management procedures, and sex makes an overall summary difficult. However, all except one experiment favor crossbreds and suggest an overall advantage of 2 to 4%. Results from the Fort Robinson experiment (Gregory et al., 166a, b); indicate that the level of heterosis was lower (3.3%) for steers on a growing fattening ration than for heifers on a low level of feeding associated with development for replacement (6.5%). The effect of heterosis on growth rate was also related to age. Heterosis tended to decrease with increasing age after approximately 1 year. Results indicate that heterosis for feed efficiency is small. However, in the time constant feeding periods of six experiments where it has been reported the crossbreds have shown a slight advantage or no difference in spite of their heavier weights throughout the feeding periods (Warwick, 168). Significant heterosis effects have been reported for carcass traits associated with growth such as carcass weight, rib-eye area (Gregory et al., 166c; Gains et al., 167), weight of boneless, closely trimmed retail product adjusted for age, and net merit computed as the value of the boneless closely trimmed retail product minus feed costs from weaning to slaughter (Gregory et al., 166c). The effects of heterosis on carcass traits not directly related to growth such as boneless, closely trimmed retail product adjusted for carcass weight, cutability, grade and palatability have been small (Kincaid, 162; Gregory et al., 166c; Gaines et al., 167). Wiltbank et al. (166) reported significant heterosis effects on age at first heat of heifers. Crossbred heifers showed heat 41 days and 35 days earlier than straightbred heifers on low and moderate levels of feeding, respectively. This is important when breeding heifers as yearlings to calve as 2-year-olds. Recent analysis on weights and measurements taken on cows ranging from 6 to years of age in the Fort Robinson experiment indicate that heterosis had a significant effect on weight, wither height and condition of cows at maturity. Crossbred cows were 21.6 kg heavier than straightbred cows. When condition score was held constant, the effect of heterosis on mature weight was reduced to 12.5 kg indicating that about 40% of the additional weight of the crossbreds was associated with fatness (L. V. Cundiff et al., unpublished data). This suggests that the effect of heterosis on metabolic size is somewhat less than that on weight unadjusted for condition (Klosterman, Sanford and Parker, 168a). The weighted averages presented in table 3 should be useful as an indication of expected heterosis effects. However, they are probably more applicable for Hereford-Angus crosses than crosses involving Shorthorns, since 13 of the 14 experiments involved Herefords and Angus while Shorthorns were included in only 5. Also, the Fort Robinson results indicated significantly less heterosis (P.05) for Angus-Shorthorn crosses than for Hereford-Angus or Hereford-Shorthorn crosses for a number of traits involving growth, feed efficiency and carcass composition (Gregory et al., 166a,b,c); indicating that, for these traits, the frequency of genes with non-additive effects are more similar between Angus and Shorthorns than between Herefords and Angus or Herefords and Shorthorns. Heterosis /or Maternal Ability and Reproduction'. The results summarized above indicate that heterosis is greatest for traits of low to moderate heritability (early growth) and least for traits of high heritability (postweaning growth and carcass merit). Thus, the primary benefit of heterosis might be expected in fertility and maternal ability of crossbred cows. Crossbred and straightbred cows are currently being compared in a number of experiments. Complete reports are not available for most of these studies but preliminary data from five experiments are given in table 4. The results are not consistent, but weighted averages show advantages for the crossbred cows of 4.7% calf crop raised and 5.6% in calf weaning weight. When the advantage in percent calf crop

5 68 CUDIFF TABLE 4. HETEROSIS EFFECTS FOR FERTILITY AD MATERAL CHARACTERS I CROSSBRED AD STRAIGHTBRED BRITISH BREED COWS o. matings Heterosis effects Location and dates Breeds ~ Fort Robinson, U.S.D.A., ebr. 162 to 168 A, H, S Miles City, c U.S.D.A., Mont. 165 to 167 A, H Virginia c 163 to 166 A, H, S Louisiana c. a 161 to 165 A, H Georgia ~' a A, H Weighted average ~ Straight- Cross- Calf Calf bred bred Calves crop wean. cows cows born weaned wt. %b %b % ~ ; a Breeds involved in experiment: A~Angus, H----Hereford, S=Shorthorn. Comparisons are made between crossbred and straightbred cows when both are raising crossbred calves, either by the same sire of a third breed or by crossbred bulls to produce calves of the same genotype. b The difference between percent calf crop in crossbred cows and percent caif crop in straightbred cows (not expressed relative to straightbred mean). e Based on table presented by Warwick (168). a A portion of the stralghtbred cows were bred for stralghtbred calves. ns nr e The results of each experiment were weighed by ~ where ns denotes number of straightbred matings and ne denotes number of crossbred matings. weaned and the advantage of maternal ability of crossbred cows are combined, a sizable advantage is indicated for the crossbred cow over the straightbred cow when both are raising crossbred calves. For example, in the Fort Robinson experiment, preliminary analysis indicates that a 14% advantage in favor of crossbred cows has been realized for pounds of calf weaned per cow in the breeding herd. This does not take into account the 3% advantage in percent calf crop weaned and the 4.5% advantage in weaning weight of crossbred calves over straightbred calves indicated in the first phase of this experiment (Cundiff et al., 16). When these effects are combined and the effects on postweaning growth and carcass merit are included, results indicated that production per cow exposed for breeding can be increased 20 to 25% by systematic crossing of British breeds. Charolais Crosses Charolais have increased rapidly in numbers in recent years and are now recognized as an important beef breed in America. Research has been hampered by scarcity of Charolais cows. Thus, most of the early research involved top cross evaluation on other breeds. Breeding Value. The first top cross evaluation, conducted in Louisiana (Damon et al., 15a,b, 160) involved Charolais, Hereford, Angus, Shorthorn, Brahman and Brangus bulls bred to Angus, Brahman, Brangus and Hereford cows (table 5). Calves by Charolais bulls were heaviest at weaning and slaughter and produced carcasses with a higher percent lean and lower percent fat. Their carcasses graded more than 2/3 of a grade lower than those of Angus and Shorthorns and more than 1/3 of a grade lower than those of Hereford sires, but their lean was as tender as that of any of the British beef breeds. Similar results were observed in top crosses on British dairy breeds in Great Britain (Edwards et al., 166) with the additional observation that feed conversion was better in Charolais x British dairy breed crosses than in British beef x British dairy breed crosses. More recently an experiment involving purebred and percentage Charolais cows (3/4 or more Charolais) in reciprocal crosses with Herefords has been reported by Klosterman, Cahill and Parker (168b) at the Ohio Station (table 6). An experiment involving purebred bulls and percentage Charolais cows in reciprocal crosses with Angus and Herefords has also been conducted by the Animal Husbandry Research Division, U.S.D.A. and Montana Agricultural Experiment Station (Pahnish et al., 168, 16) at Miles City, Montana (table 7). A similiar project is in progress at the Missouri Station. These experiments and other top cross studies have confirmed that Charolais cattle are superior in pre- and post-weaning growth rate and produce carcasses grading 1/3 to 2/3 of a grade lower which contain a higher pro-

6 ~q Z Z Z m z ~ r/? m ~ z g M 4 o m 0 Z M M M tm o~ CROSSBREEDIG CATTLE FOR BEEF PRODUCTIO ~22~'" 44~64~ ~mm~m~ ~W6WWdU 6666~6 m e~.~ ~.5-- ~OOQQ 6 TABLE 6. OHIO RESULTS FROM HEREFORD, CHAROLAIS AD RECIPROCAL CROSSBREDS ~ Here- Cross- ford Charolais bred Heterosis umber day weaning weight, kg % Avg daily gain on feed, kg 0.8 1, % Slaughter weight, kg 385. i % Edible portion, % a/o Fat trim, % I% Bone, % % Carcass grade b , /15 grade Tenderness e Klosterman et al. (168). Low, average and high good--16, 17, 18. e 1--extremely tough to 10--~extremely tender. portion of lean and less fat than cattle of British beef breeds. Fertility of Charolais cattle has not been adequately characterized due to the shortage of cows in experimental herds and the amount of time and number of matings required for precise estimates. It is generally recommended that Charolais bulls should not be bred to straightbred or crossbred heifers of British breeds to avoid calving difficulty in their first parturition. Edwards et al. (166) indicated that Charolais bulls appear to cause more calving difficulty than British beef breeds. This was associated with a longer gestation period and heavier birth weights of Charolais sired calves. Klosterman et al. (168b) reported that Charolais cows tended to wean smaller percentages of calves than Herefords when bred straight, but a higher percentage when crossed. Hereford cows weaned a lower percent of crossbred than straightbred calves and greater calving difficulty was experienced in Hereford cows with Charolais sired calves than straightbred calves. However, more than 80% of the total calving difficulties involved first-calf, 2-year-old heifers. Only limited calving problems were experienced following the first calf regardless of the breed or cross. Charolais, Hereford and Angus sires did not differ significantly in causing calving difficulty in Hereford and Charolais cows in the Missouri experiment (Sagebiel et al., 168). However, Charolais and Hereford sires did cause more difficulty and differed significantly when bred to Angus cows. Calving difficulty was experienced in 3~o and 2e/o of the Angus cows bred to Charolais and Hereford bulls, respectively. Calving difficulty was greater in first calf heifers bred to Charolais bulls than in second and third calf cows.

7 700 CUDIFF TABLE 7. U.S.D.A. AD MOTAA (MILES CITY) RESULTS FROM HEREFORD (H), AGUS (A) AD CHAROLAIS (C) AD RECIPROCAL CROSSBREDS Trait H A C HA HC AC Preweaning (sexes combined) a umber Birth weight, kg Heterosis (%) day weight, kg Heterosis (%) Weaning score Heterosis (unit) Postweaning (steers) b umber Days on feed * A.D.G. on test, kg Heterosis (%) Gain per cwt, TD Heterosis (%) Carcass grade Heterosis (unit) a Adapted from Pahnish et al. (16). b Adapted from preliminary unpublished summary prepared by Pahnish et al. c Steers were slaughtered as they reached relatively uniform final weights. The average final weight was kilograms. a Lower values are for higher grades; Prime: High (2), Middle (4), Low (6); Choice: High (8), Middle (10), Low (12); Good: High (14), Middle (16), Low (18). Data to characterize maternal ability of the Charolais is limited. Melton et al. (167) reported that milk production of Charolais cows was persistantly higher than that of Angus and Herefords measured in six periods from 77 to 224 days post-partum. Partitioning of recently published data from the Miles City experiment (Pahnish et al., 168) indicates that about 7 kg of the 45 kg advantage of Charolais over Hereford and Angus in weaning weight was due to an advantage in maternal ability. This is relatively small compared to the estimated 38 kg advantage associated with transmitted additive gene effects expressed in the individual itself. Heterosis Effects. Heterosis effects in first cross calves between Charolais and British beef breeds have been reported by Klosterman et al. (168b, table 6) and Pahnish et al. (168, 16, table 7). Also, an analysis has recently been completed on postweaning and carcass traits of short-fed (183 to 18 days) and long-fed (251 to 267 days) heifers in the Missouri experiment (John F. Lasley et al., unpublished mimeo, table 8). The effects of heterosis on weaning weight (steers and heifers combined) and postweaning gain (steers only) are in close agreement for Hereford-Charolais crosses in the Ohio and Miles City experiments. Somewhat greater heterosis has been observed in the Missouri experiment for weaning weight of this cross. This may be associated with the difference in management involving fall calving and creep feeding in the Missouri experiment. Results from the Missouri station (Lasley et al., 16) indicate that the effect of heterosis on postweaning growth is greater in Charolais-British crosses when they are fed out in a short period of 183 to 18 days immediately after weaning than when they are fed out in a longer postweaning period of TABLE 8. HETEROSIS EFFECTS AMOG HERE- FORD (H), AGUS (A) AD CHAROLAIS (C) BREEDS I SHORT-FED AD LOG-FED HEIFERS AT THE MISSOURI STATIO (Unpublished Data) Trait Short-feda Long-feda HA HC AC HA HC AC o. crossbreds o. straightbreds % % % % % % Initial wt Avg daily gain Slaughter wt S -- 1 Carcass grade } Tenderness Retail cuts, wt S S 3 2 Fat trim, wt Bone, wt Retail cuts, % Fat trim, % Bone, % a Short-fed: fed out immediately following weaning in a 183 to 18 day period; Long-fed: fed out immediately following weaning in a 251 to 267 day period. The same ration was used in both periods.

8 CROSSBREEDIG CATTLE FOR BEEF PRODUCTIO to 267 days. A significant breed by method of management interaction was detected in the Ohio data for edible portion per day of age (Klosterman et al., 168b). Cattle which were creep fed and finished out immediately following weaning produced more pounds of edible portion per day of age than those in the deferred system (not creepfed, wintered to gain.454 to.567 kg per head daily, grazed for about 60 days without grain and then fattened in dry lot). However, the advantage of Charolais and Charolais-Hereford crosses over Herefords was greater when creep fed and finished immediately after weaning than in the deferred system indicating that the rapid growth rate of the large Charolais breed can be utilized best by liberal feeding at a young age. A significant breed-management system interaction was also reported by Klosterman et al. (168b) for marbling score. The Hereford and crossbred calves exceeded the Charolais more in marbling at the younger age than at the older age of the deferred system. Results from Miles City (table 7) and Missouri (table 8) suggest that the effect of heterosis on weaning weight and postweaning growth may be less in Charolais- Angus and Charolais-Hereford crosses than in Hereford-Angus crosses. There is a tendency in both experiments for heterosis to be less in Charolais-Angus than Charolais- Herefords. The effect of heterosis on carcass quality and composition has also been small in all three experiments (Klosterman et al., 168b; Pahnish et al., 168, 16; John F. Lasley et al., unpublished mimeo). Yet, the average performance of the breeds would indicate that there are marked differences between breeds in frequency of genes effecting growth rate and carcass composition and grade. The similar if not lower levels of heterosis in Charolais-British breed crosses suggests that the genes responsible for expression of these traits are quite additive in their effects. This indicates that with respect to these traits, the primary benefit of using Charolais in crossbreeding programs with British breeds will be to combine desired characteristics--more specifically to increase growth and proportion retail product and to decrease fat trim of the British breeds and improve carcass grade of the Charolais. The effect of heterosis in Charolais-British crosses on fertility and maternal ability is not known. This is currently being evaluated TABLE. BRAHMA-BRITISH CROSSBREED- IG--CALF CROP WEAED EXPRESSED AS DEVIATIOS FROM BRITISH AVERAGES (WARWICK, 168) a Dams Brahman- Sires British British Brahman British 0 -[-7.6% % Brahman --2.% +3.% % a Weighted average figures from Texas Tech., Monog. o. 1, 164 and Florida Bull. 673, 164. at Miles City and Ohio and is to be done at Missouri. Brahman Crosses with British Breeds Considerable research has been conducted in the Southern region of the United States on crossing of Brahman and British breeds through the cooperative efforts of U.S.D.A. and Agriculture Experiment Sations involved in Southern Regional Project S-10. Much of these data were summarized and reported by Kincaid (162). More recent reports have been included in the reviews by Mason (166) and Warwick (168). Some of the more pertinent results are summarized in tables, 10, 11 and 12. Breeding Value. The results indicate that straightbred Brahmans are lower in calf crop weaned than British cows (table ). This is due to lower calving rate and lower survival from birth to weaning (Cartwright et al., 164). Weaning weight of straightbred Brahman calves have been somewhat higher than those of Herefords and Shorthorns and similiar to Angus. Results indicate that the maternal ability of the Brahman is superior to the Hereford (Damon et al., 161; Kincaid, 162; Cartwright et al., 164) but less than that of the Angus (Damon et al., 161). Herefords appear to be superior to the Brahman in preweaning growth impulse (Damon TABLE 10. FERTILITY OF BRITISH, BRAH- MA AD BRITISH-BRAHMA CROSSBRED COWS I LOUISIAA a % calf crop o. Breed of cow matings Born Weaned Angus Hereford Brahman Angus-Brahman b Hereford-Brahman b a Turner et al. (168). b Reciprocals combined.

9 702 CUDIFF TABLE 11. BRAHMA-BRITISH CROSSBREED- IG--GAI TO WEAIG EXPRESSED AS DEVIATIOS FROM BRITISH AVERAGES (WARWICK, 168) '~ Dams Brahman- Sires British British Brahman British % 1 I. 4% Brahman 10.8% 15.6% 1.2% a Adapted from Southern Series Cooperative Bull. o. 81, 162, summarizing extensive research in several Southern states. et al., 161; Cartwright et al., 164). Postweaning growth of the Brahman is less than that of straightbred British breed calves (Kincaid, 162; Cartwright et al., 164). Results indicate that when slaughtered as yearlings, British bred steers have higher carcass grades and show higher percentages of fat than Brahman steers, while Brahman steers have higher percentages of lean and bone (table 12). Lean to bone ratios in the th rib favor the British breeds slightly. Tenderness as measured by the Warner-Bratzler shear technique and eating quality as measured by paired eating tests have shown the British breeds significantly better than the Brahman. On the average, eating quality and tenderness declines in British-Brahman crosses as Brahman blood increases (Kincaid, 162). Heterosis Effects. Results indicate that the effect of heterosis on calf crop weaned in F1 Brahman-British calves is small. The data summarized by Warwick (168, table ) would indicate that it is only i%. However, the effect of heterosis on fertility of the crossbred Brahman-British cow is quite large TABLE 12. BRAHMA-BRITISH CROSSBREED- IG--SOME GROWTH AD CARCASS CHARACTERS OF FED STEERS) (WARWICK, 168) ~ Brahman- British British crosses Brahman Slaughter age (days) Carcass wt. per day of age (kg) Dressing percent th rib cut % lean 52.I % fat % bone Carcass grade +good avg good -~-st. Warner-Bratzler shear b Adapted from Southern Series Bull. o. 81, 162, summarizing data from several Southern states. b Kilograms of force required to shear a 1-inch core of cooked meat. Smaller figures indicate more tender meat. (13.8%, table ). Table 10 gives additional data from Louisiana (Turner, Farthing and Robertson, 168) indicating heterosis effects of 12.1% in Brahman-Angus cows and 18.8% in Brahman-Hereford cows. Heterosis is expressed to a high degree in weaning weight of first cross calves and in weaning weight of calves from crossbred cows. Cartwright et al. (164) estimated that the effect of heterosis in first cross Hereford- Brahman calves was 15.% and that the effect on maternal ability of crosbred dams was.5%. In the data summarized by Warwick (168, tables, 11) crossbred Brahman-British calves exceeded British straightbreds by about 11% in weaning weight and the crossbred cow exceeded the British cows in both calf crop weaned and weaning weight. The combined advantages of 7.6% in calf crop and 15% in weaning weight demonstrates that the Brahman-British cow is highly productive when bred to British bulls. The effect of heterosis on postweaning gain in Brahman-British crosses, although somewhat lower than that for preweaning gain, if also quite high. Cartwright et al. (164) estimated that it was 11.0% in Hereford- Brahman crosses, Kincaid (162) reported that the effect of heterosis on growth from birth to about 15 months of age was 11.5%, which was 7% above the gain of British breeds. Kincaid (162) reported that carcass traits not directly related to growth rate showed little evidence of heterosis and crosses usually were near the average of their parents (table 12). In general, heterosis effects are similar in pattern, being inversely related to heritability, but they are greater among Brahman-British crosses than among crosses of the British breeds. For example, Kincaid reported that heterosis effects of 11.5% and 4%, respectively, for gain from birth to about 15 months of age. As was pointed out by Willham (16) this is to be expected since the Brahman is obviously more divergent from the British breeds than they are one from another. However, an additional factor may share responsibility for the extremely large heterosis effects observed in Brahman- British breed crosses. It is generally recognized that British breeds are not well adapted in the Southern regions of the United States. or is this region as tropical as the conditions under which the Brahman (Zebu) originally

10 CROSSBREEDIG CATTLE FOR BEEF PRODUCTIO 703 evolved. It seems logical that heterosis would be maximized when comparison is made in an intermediate environment between the crossbred (additively intermediate) genotype and the average of the two parent breeds, neither of which are perfectly adapted. The presence of genotype-environment interaction involving Brahman, and British breeds and their crosses has been demonstrated in several studies. Brahmans and their crosses are more heat tolerant than British breeds (Kibler, 157). Rollins, Carroll and Ittner (164) observed that 3/4 Hereford-I/4 Brahman calves gained more rapidly than Hereford calves in the summer both on pasture and in the feed lot, but the reverse was true for feed lot gains during the fall and winter in the Imperial Valley of California. Crosses with Breeds Based on Brahman-European Foundations ew breeds have been used to only a limited extent in crossbreeding experiments. In the data reported by Damon et al. (15a,b; 160) calves by Brangus bulls were lighter at weaning than those by Charolais, and Hereford and slightly lighter than those by Shorthorn and Brahman (table 5). Their postweaning gain and carcass composition was similar to Brahman sired calves. Warner-Bratzler shear values indicated their lean was somewhat more tender than Brahman but less tender than Charolais or British breed sired calves. However, Brangus cows weaned heavier calves than Angus, Hereford or Brahman females when all were bred to the same six breeds of bulls (Damon et al., 15a) suggesting that heterosis is retained in the Brangus for maternal ability. Heterosis for weaning weight of first cross Angus-Brangus and Brahman- Brangus calves of 3.6% and 3.8%, respectively, was less than that of.7% in Angus-Brahman crosses (Damon et al., (161). Heterosis effects for calving percent in crossbred Angus-Brangus and Brahman- Brangus cows of 3.7% and 11.6%, respectively, and 12.1 for Angus-Brahman cows% were reported by Turner et al. (168). In another study still in progress, straightbred Santa Gertrudis, Angus and Polled Herefords are being compared with rotation crosses and criss crosses of the same three breeds. To date the Santa Gertrudis has had faster growth rates both before and after weaning than either of the other straightbred groups and has exceeded most crossbred groups. There has been some indication of hybrid vigor for growth in crosses with other breeds (Warwick, 168). Also, a recent study at the Texas station has shown that Santa Gertrudis in top crosses with several other breeds ranked above Brahman and Hereford but below Charolais and Charbray in general combining ability for 180-day weaning weight and final weight at 11 to 16 months of age (Warwick, 168). Dairy and Dual Purpose-- Beef Breed Crosses Several dairy breeds are receiving increased attention as prospects for crossbreeding in commercial beef production. Dairy breeds vary greatly in production character- istics. Holsteins gain more rapidly than Herefords and Angus but rate of gain in Jerseys is less (Cole et al., 163). Herefords and Angus grade significantly higher but are fatter than Holsteins and Jerseys (Cole et al., 163). Steaks from Jerseys were more tender than those from other breeds in the Tenessee experiment (Ramsey et al., 163), but differences between Jerseys and Herefords were not significant. Brown Swiss cows have been handled under range conditions along with the Charolais, Angus and Hereford cows at Miles City, Montana (Pahnish et al., 168, 16). Crossbred calves out of Brown Swiss cows sired by Charolais, Angus and Hereford bulls have been heavier at weaning than crossbred calves out of Charolais, Angus and Hereford cows sired by the same bulls (table 13). The crossbreds with Brown Swiss breeding were comparable to the beef crossbreds in postweaning gain and were only 1/6 of a grade lower in carcass grade. In specific beef x Brown Swiss crosses, the Charolais x Brown Swiss crosses were the growthiest, but the Brown Swiss crosses sired by bulls of the British breeds graded more favorably in the carcass. An extensive heterosis project involving Brown Swiss, Holsteins, Angus and Hereford cattle in a semi-confinement fall-calving management program is currently in progress at the Iowa Station (R. L. Willham, personal communication). Preliminary analysis of weights taken at birth, 60, 0, 120 and 180 days on the first calf crop (36 calves) indicate major maternal differences and ranked Holsteins over Brown Swiss, Angus and Herefords in that order. Breed of sire effects were

11 704 CUDIFF TABLE 13. MILES CITY, U.S.D.A. AD MO- TAA, RESULTS: COMPARIG BROW SWISS DAMS AD BEEF BREED DAMS I CROSSES WITH BEEF BREED SIRES ~ (205 DAY WEAIG WT., SEXES COMBIED) Cross b umber Mean H B 32 kg 253 A B C B Comparison Mean difference I-IB-HC AB-AC 23** 12 HB-HA CB-CA 41"* 44** AB-AH CB-CH 34** 43** a Pahnish et al. (15). ~H=Hereford, A=Angus, C~Charolais, B~Brown Swiss; breed of sire is identified by the first letter and breed of dam by the second. ~ P~.OI. a less important source of variation, but favored Brown Swiss over Holsteins which in turn were heavier than Angus and Herefords. Heterosis effects for 180 day weight were.1% for beefxbeef crosses, 6.4% for beef x dairy and 6.4% for dairy x dairy crosses. Feed consumption of the first calf dairy heifers was greater than that of the first calf beef heifers during the lactation period, though body weight change favored the beef heifers. Rebreeding performance was better in Angus, Herefords and Holsteins than in Brown Swiss. A heterosis project involving Milking Shorthorn and Angus straightbreds and reciprocal crosses is in progress at the Indiana Station (K. J. Drewry and T. G. Martin, personal communication). To date, straightbred and crossbred calves out of Milking Shorthorn dams have gained faster before and after weaning than the straightbreds and reciprocal crosses out of Angus cows. Straightbred Angus have graded average choice while the other three breed-groups have graded low choice. Appreciable heterosis has been expressed for growth. Conclusions Crossing British breeds will combine desired characteristics of Herefords, Angus and Shorthorns but the major benefit will be accrued through the cumulative effects of heterosis on fertility, maternal ability and growth rate. It appears conservative to conclude that production per cow exposed for breeding can be increased 20 to 25~o by systematic crossing of British breeds. About half of this advantage is dependent upon the use of crossbred cows to take advantage of heterosis for maternal ability and reproduction. More data are needed to characterize Charolais straightbreds and crossbreds for fertility, maternal ability and productive efficiency. Data already available indicate that they have promise as an important sire breed. They transmit outstanding growth rate and improve carcass composition primarily as a result of their superior breeding value for these characteristics. However, they reduce carcass quality grade. The role of the Brahman in the South in crossbreeding programs for commercial production has long been recognized. The Brahman and British breeds compliment each other for a number of production traits and express heterosis to a higher degree than has been observed between any other breeds. Data on new breeds based on Brahman- British foundations are too limited to draw definite conclusions. With the exception of superior milk production, rapid growth and large mature size of Holsteins and Brown Swiss, the same is true with regard to dairy breeds and other exotic sources of germ plasm just now coming on the scene. Literature Cited Butler, O. D., T. C. Cartwright, L. E. Kunkle, F. A. Orts, G. T. King and D. W. Lewter Comparative feedlot performance and carcass characteristics of Hereford and Angus steers. J. Anim. Sci. 21:28. Cartwright, T. C., G. F. Ellis, Jr., W. E. Kruse and E. K. Crouch Hybrid vigor in Brahman Hereford crosses. Texas Agr. Exp. Sta. Tech. Monogr. 1. Cole, J. W., C. B. Ramsey, C. S. Hobbs and. R. S. Temple Effects of type and breed of British, Zebu and dairy cattle on production, palatability and composition. I. Rate of gain, feed efficiency and factors affecting market value. J. Anim. Sci. 22:702. Cundiff, L. V., K. E. Gregory, R. M. Koch, G. E. Dickerson and R. D. Humphrey, 16. Hybrid vigor in beef cattle. 16 ebraska Beef Cattle Rep. E.C p Damon, R. A., Jr., S. E. McCraine, R. M. Crown and C. B. Singletary. 15a. Performance of crossbred beef cattle in the Gulf Coast region. J. Anim. Sci. 18:437. Damon, R. A., Jr., S. E. McCraine, R. M. Crown and C. B. Singletary. 15b. Gains and grades of beef steers in the Gulf Coast region. J. Anita. Sci. 18: Damon, R. A., Jr., R. M. Crown, C. B. Singletary and S. E. McCraine Carcass characteri.~tics

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