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IMPLICATIONS OF BREED EVALUATIONS
Posted by : Larry V. Cundiff on Wednesday, December 21, 2005 - 12:37 PM
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| Roman L. Hruska U.S. Meat Animal Research Center |
| Agricultural Research Service |
| U.S. Department of Agriculture |
| Clay Center, Nebraska |
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| Introduction |
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Breeds are an important genetic resource. Breeds can be crossed to benefit from significant effects of heterosis on components of production efficiency and to optimize performance levels in crossbreds that are important in beef production. In this presentation, research results will be reviewed focusing on effects and utilization of heterosis and breed differences, and on the importance of matching genetic potential with consumer preferences and the climatic environment.
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| Heterosis |
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A crossbreeding experiment involving Herefords, Angus, and Shorthorns demonstrated that weaning weight per cow was increased by about 23% due to beneficial effects of heterosis on survival and growth of crossbred calves and on reproduction rate and weaning weight of calves from crossbred dams (Figure 1). More than half of this advantage was due to use of crossbred cows. Effects of heterosis are greatest for longevity and lifetime production of cows (Table 1).
For comprehensive traits such as lifetime production, cumulative effects of heterosis are rather large and the performance of each specific cross usually exceeds that of either parent breed. For example, longevity and lifetime production of Hereford x Angus and Angus x Hereford cows was significantly greater than that of either Straightbred Angus or Herefords. Crossing of Bos indicus and Bos taurus breeds yield even higher levels of heterosis, averaging about twice as large as estimates reported for corresponding traits in crosses among Bos taurus breeds.
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Rotational Crossbreeding |
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In the experiment involving Herefords, Angus, and Shorthorns conducted at the U.S. Meat Animal Research Center (MARC), it was demonstrated that significant levels of heterosis were maintained from generation to generation by rotational crossbreeding of Herefords, Angus, and Shorthorns (Figure 2). The level of heterosis retained was proportional to expected heterozygosity (Gregory and Cundiff, 1980). It is important to use breeds that are reasonably comparable in rotational crossbreeding systems to provide for uniformity in traits such as birth weight to minimize calving difficulty, size and milk production to stabilize feed requirements in cow herds, and carcass and meat characteristics. Breed composition fluctuates widely from one generation to the next with rotational crossbreeding. For example in two-breed rotation after the sixth generation and on the average over all generations, 67% of the genes of the cows are of the breed of their sire and 33% are of the breed of their grandsire, the latter being the same as the breed to which they are to be mated.
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Composite Populations |
Composite populations, developed by inter se mating of animals resulting from crossing of two or more breeds, have management requirements that are comparable to straight-breeding. Results of a comprehensive experiment involving four generations of inter se mating in three composite populations demonstrated that significant levels of heterosis are retained in composite populations (Gregory et al., 1999). In this experiment performance of each composite population (Composite MARC I was 1/4 Charolais, 1/4 Braunvieh, 1/4 Limousin, 1/8 Hereford, and 1/8 Angus; Composite MARC II was 1/4 each Simmental, Gelbvieh, Angus, and Hereford; and Composite MARC III was 1/4 each Pinzgauer, Angus, Hereford, and Red Poll) was compared to performance of the purebreds that contributed to the foundation of each Composite population. Effects of heterosis (F1 minus Purebreds) and retained heterosis in advanced generations (F2 = F1 X F1 matings, F3 = F2 X F2 matings, and F4 = F3 X F3 matings) are summarized in Table 2. Heterosis was maintained proportional to heterozygosity in composite populations. Since heterosis is retained proportional to heterozygosity, significant levels of heterosis can be maintained by rotational crossing of F1 seedstock (e.g, F1 cross Gelbvieh X Angus, or Simmental X Hereford) or by rotational crossing of composite populations (e.g., Brangus, Beefmaster) as well.
Uniformity of cattle and greater consistency of end product can be provided for with greater precision by use of F1 seedstock or composite populations than by use of rotational crossing of purebreds. For example, with current pricing systems, cattle with 50:50 ratios of Continental to British breed inheritance have more optimal carcass characteristics, experiencing fewer discounts for excessive fatness (yield grade 4 or more) or for low levels of marbling (USDA Standard quality grades or less) than cattle with lower or higher ratios of Continental to British inheritance. This is caused by a strong genetic antagonism between USDA quality grade and percentage retail product (Figure 3). Retail product is closely trimmed (0.0 inches) boneless steaks, roasts, and lean trim (ground beef containing 20% fat). In the Germplasm Utilization Program at MARC, steers representing Continental European breeds (Charolais, Simmental, Braunvieh, Gelbvieh, Pinzgauer) excelled in retail product percentage but had difficulty grading USDA Choice because of lower levels of marbling. British breeds (e.g., Angus, Hereford, Red Poll) excelled in USDA quality grade because of higher levels of marbling but had reduced retail product yield due to excessive fat thickness and fat trim.
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Breed Differences |
Table 1 shows the mating plan for the first eight Cycles of the Germplasm Evaluation (GPE) Program at MARC. Each Cycle is an experiment conducted over a time span of about 10 years. Topcross performance of 34 sire breeds has been evaluated in F1 calves out of Hereford, Angus, or composite MARC III (1/4 Angus, 1/4 Hereford, 1/4 Red Poll, and 1/4 Pinzgauer, starting with Cycle V) dams. Hereford and Angus sires have been used in each Cycle of the program to provide ties for analysis of data pooled over Cycles. Some of the Hereford and Angus sires used in Cycle I were repeated in Cycles II, III and IV (60'-70's sires). Later, many of the Hereford and Angus sires used for the first time in Cycle IV were repeated in Cycle V (80's sires). Similarly, many of the Brahman sires used in Cycle III (70's sires) were repeated in Cycle V and compared to a new sample of Brahman sires born in the 1980's (80's sires). As a general rule in each Cycle, about 200 progeny per sire breed were produced from artificial insemination (AI) to 20-25 sires per breed. Sires were sampled representing young herd sire prospects (non progeny tested sires) for each breed. Starting with Cycle VII, about half of the sires sampled were chosen from lists of the 50 most widely used bulls in each breed according to registrations.
Calves were born in the spring and weaned in the fall at about 7 months of age. Male calves were castrated within 24 hours of birth. Following weaning, steers were fed a diet containing about 2.8 Mcal metabolizable energy per kg dry matter. Data will be presented for steers that were slaughtered in three to four slaughter groups spaced 21 to 28 days apart. All F1 females were retained to evaluate growth, age at puberty, reproduction, and maternal performance in three-way cross progeny produced at 2- through 7- or 8-years of age.
Prominent Bos taurus breeds. In Cycle VII of the GPE Program, the seven most prominent beef breeds in the U.S., according to registrations in breed associations (National Pedigreed Livestock Council, 2002), were evaluated (Table 4). Angus, Hereford, Limousin, Simmental, Charolais, and Gelbvieh had been characterized in Cycle I or Cycle II of the GPE Program (Table 3). Red Angus cattle were evaluated for the first time in Cycle VII.
Sire breed means for final slaughter weight (445 days) and certain carcass and meat traits are shown in Table 6. The differences for slaughter weight (445 days) between progeny of Continental sire breeds compared to British sire breeds were considerably less than when they were evaluated 25-30 years earlier. However, differences between Continental and British breeds in retail product percentage, marbling score, and percentage grading USDA Choice were about the same as they were in Cycle I and Cycle II of the program. Carcasses from progeny of Limousin, Gelbvieh, Charolais, and Simmental sires had significantly higher retail product percentages and yield grades than carcasses from progeny of Hereford, Angus, and Red Angus sires. However, marbling was significantly greater in progeny of Red Angus and Angus sires than in progeny of Charolais, Hereford, Gelbvieh and Limousin sires. Rib steaks from Angus sired progeny were significantly more tender than those from Gelbvieh sired progeny according to shear force evaluations. British breed crosses (Table 7) had a higher percentage of yield grade 4 carcasses than continental European breed crosses (Tables 7 and 8). Results in Cycle VII are consistent with earlier results indicating that cattle with 50:50 contributions of Continental to British inheritance are more optimal for current market grids than cattle with lower or higher ratios of Continental to British inheritance.
Post-weaning growth and puberty traits are shown in Table 9. Sire breed differences between British and Continental sire breeds for body weights at 400 or 550 days in progeny of sires born in Cycle VII (born in 1999-2000) were not as great as they were in Cycle I and II (1970-1974) of the GPE Program and reflected considerable re-ranking among breeds. However, hip heights and frame scores were significantly greater for heifers with Simmental, Charolais, and Limousin sires than for those with Angus and Red Angus sires. Age at puberty was greater in Limousin sired heifers than all other sire breeds and younger in Gelbvieh sired heifers than in Hereford sired heifers. Breeds that have had a history of selection for milk production (e.g., Simmental and Gelbvieh) reached puberty earlier than breeds that have not been selected for milk production (all other breeds).
Data reported for reproduction and maternal performance are especially preliminary, representing only the first of seven calf crops to be produced by the F1 females (Table 10). Breed of sire of the F1 dams calving at 2 years of age was not a significant source of variation for any of the traits summarized, except 200-day weaning weight per calf weaned. Weaning weights of progeny raised by F1 females with Gelbvieh and Simmental sires were significantly heavier than those with Charolais, Limousin, and Angus sires. Weaning weights of progeny raised by F1 females with Hereford sires were significantly lighter that those by any other sire breed, except Red Angus. Contrasts between British and Continental European breeds are less than half as great for direct and maternal weaning weight today as they were 25 to 30 years ago.
Tropically adapted breeds. Use of Bos indicus x Bos taurus crosses (e.g., Brahman X Hereford) is greatly favored in the subtropical regions of the U.S. In a cooperative effort between the Subtropical Agricultural Research Station, (ARS, USDA and the University of Florida), Brooksville, Florida and MARC, weaning weight per cow exposed was significantly greater for the Bos indicus x Bos taurus F1 crosses (Brahman x Hereford, Brahman x Angus, Sahiwal x Hereford, Sahiwal x Angus) than for the Bos taurus x Bos taurus F1 crosses (Hereford x Angus, Angus x Hereford, Pinzgauer x Hereford, Pinzgauer x Angus) at both locations, but the advantage was especially large in Florida (Figure 4). Results at MARC also indicated that cow efficiency (pounds of calf gain per unit of feed consumed by the cow and calf), estimated during lactation in summer months, was exceptional for Bos indicus x Bos taurus relative to Hereford-Angus crosses (Table11), which were in turn relatively efficient compared to other Bos taurus x Bos taurus crosses (Table 12). Reproduction rate, weaning weight per cow exposed and cow efficiency is outstanding in Bos indicus x Bos taurus F1 crosses, especially in subtropical climatic environments, but their advantages are tempered by older age at puberty and reduced meat tenderness as the proportion of Bos indicus increases. Concerns about meat quality and reproduction rate at young ages have prompted introduction and evaluation of other tropically adapted germplasm in cooperative research efforts involving MARC and research stations in subtropical regions of the U.S. (i.e., Texas, Oklahoma, Florida, Georgia, and Louisiana) with contributing projects to Regional Project S-277.
In Cycle V of the Germplasm Evaluation Program at MARC (Table 13), tropically adapted Tuli, Boran and Brahman sire breeds were evaluated relative to Hereford and Angus crosses. The Tuli, a Sanga type of cattle (non humped), originates from Africa. Semen from nine Tuli bulls was imported from Australia for use in the experiment. Tuli were introduced into Australia from Zimbabwe in 1990 by embryo transfer. Semen from eight Boran bulls was imported from Australia for use in the experiment. Borans are a pure Zebu breed (Bos indicus, humped) that evolved in southern Ethiopia and are believed to have been developed for milk and meat production under stressful tropical conditions. Boran cattle were also introduced into Australia from East Africa (Zambia) by embryo transfer at the same time as the Tuli.
Performance of Nellore crosses, also shown in Table 15, were estimated by adding the deviation of Nellore crosses from Hereford and Angus crosses produced in Cycle IV to the mean of Hereford and Angus crosses produced in Cycle V (The least significant differences between Nellore crosses and other breeds can be approximated by multiplying 1.5 times the least significant difference shown in Table 15 for Cycle V contrasts).
Results indicate that Tuli cattle, produce crossbred progeny with carcass and meat characteristics more similar to progeny sired by British Bos taurus breeds (i.e., Hereford and Angus) than to progeny sired by Bos indicus breeds (i.e., Brahman or Boran) (Table 13). However, Tuli crosses had relatively low average daily gains. Performance of Nellore crosses was comparable to that of current Brahman crosses for preweaning and postweaning growth rate, weight and percentage of retail product. Tuli and Boran crosses were significantly younger at puberty and had higher reproduction rates as 2-year-olds than Brahman crosses (Table 14). However, at 3 years of age or older, reproduction rate did not differ among Nellore, Brahman, Boran and Tuli sired females. At all ages, maternal weaning weight was greater for Nellore and Brahman than Boran sired F1 cross females which were in turn greater than Tuli sired F1 cross females. Tuli germplasm may be useful to replace a portion of Bos indicus breeding and maintain tropical adaptation without detrimental effects on meat tenderness, provided they are crossed with other breeds that optimize size and growth rate. Cooperative research efforts have been completed recently to evaluate reproduction and maternal performance of F1 cows by Tuli, Boran and Brahman sires at research stations located in subtropical regions of the U.S. (i.e., Florida, Georgia, Texas, Louisiana and Oklahoma. However, data have not yet been pooled and analyzed over all locations to assess the importance of genotype-environment interactions for these traits.
In Cycle VIII of the GPE Program Brangus, Beefmaster, Bonsmara, and Romosinuano are being evaluated relative to Hereford and Angus crosses. Beefmaster and Brangus were included in Cycle VIII because of they are prominent breeds used extensively in subtropical regions of the U.S. ranking 8th and 9th in registrations among U.S. beef (Table 4). Bonsmara are a composite breed that was developed in South Africa from approximately 50% Africaner (an African Sanga breed), 25% Hereford, and 25% Shorthorn foundation matings. Semen was used from 19 Bonsmara bulls purchased from Mr. George Chapman, Amarillo, TX who imported the breed into the United States. Semen from 20 Romosinuano bulls was used. The Romosinuano breed was developed primarily in Colombia and introduced into the U.S. from Venezuela at the Subtropical Agricultural Research Station (STARS), ARS, USDA and the University of Florida, Brooksville, FL. The Romosinuano is a Criollo (domestic) breed of Central America that traces back to Bos taurus cattle introduced from Europe about 400 to 500 years ago.
Preliminary data for growth and carcass traits of steers are summarized in Table 15. These results are preliminary representing only the first of two calf crops to be evaluated in this Cycle of the program. Beefmaster, Brangus, Angus, and Hereford have not differed significantly in final slaughter weight (432 days), all of which were significantly heavier than Bonsmara and Romosinuano. Angus had significantly lower percentages retail product but higher levels of marbling and a greater percentage grading USDA Choice than the other breeds.
Half of the Brangus, Beefmaster, Bonsmara, and Romsinuano females being produced at MARC are being transferred at about 8 months of age from MARC to Louisiana State University to evaluate Genotype-environment interactions. Thus, data summarizing growth and puberty characteristics of females in Tables 16 and 17, are especially preliminary. The Brangus, Beefmaster, Brangus, and Romsinuano sired progeny represent only about 25% of the females to being evaluated in the cooperative experiment. Early results on growth of heifers are consistent with that of steers indicating that Romosinuano and Bonsmara females expressed lighter body weights at 400 or 550 days of age and shorter hip heights at 550 days of age than Beefmaster, Brangus, Angus, or Hereford. Early indications are that Romosinuano may reach puberty at significantly older ages than Angus, Herefords and Brangus. However, differences among sire breeds in pregnancy rate have not been significant to date.
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Implications |
The beef industry is challenged to 1) reduce costs of production to remain competitive in global markets, 2) match genetic potential with the climate and feed resources available in diverse environments, 3) reduce fat and increase leanness of products to gain greater acceptance of consumers, and 4) improve palatability, tenderness, and consistency of beef products. Use of heterosis and breed differences through use of crossbreeding or composite populations, and selection of breeding stock to exploit genetic variation within breeds can all be used to help meet these challenges.
Effects of heterosis increase production per cow about 20 to 25 percent in Bos taurus crosses (e.g., Angus X Hereford) and at least 50 percent in Bos indicus X Bos taurus breed crosses (eg., Brahman X Shorthorn). Significant levels of heterosis are maintained by rotational systems of crossbreeding and in composite populations. Rotational systems of crossbreeding provide for more effective use of heterosis than composite populations for any specific number of breeds. However, uniformity of cattle and greater consistency of end product can be provided for with greater precision by use of F1 seedstock or composite populations than by use of rotational crossing of pure breeds.
No one breed excels in all traits of importance to beef production. Thus, crossing of two or more breeds can be used to optimize performance levels. In temperate environments, genetic potential for retail product and marbling are more nearly optimized in cattle with 50:50 ratios than in cattle with higher or lower ratios of Continental to British inheritance.
To limit costs of production and improve efficiency of production a strong influence of tropically adapted germplasm is needed in subtropical regions of the U.S. In the hotter and more humid climates of the Gulf Coast, about 50:50 ratios of Bos indicus to Bos taurus inheritance may be optimal. A little further north (e.g., Southeastern Oklahoma, central Arkansas, Tennessee and parts of North Carolina), 25:75 ratios of Bos indicus: Bos taurus inheritance may be optimal in cow herds. In temperate climates (e.g., Nebraska), crosses with 50% or more Bos indicus inheritance suffer increased mortality when calves are born in colder seasons and reduced average daily gains in feedlots during winter months. Use of F1 Brahman cross cows, Nellore, or Boran F1 cross cows or rotational crossing of composite breeds such as Beefmaster, Brangus, Bonsmara, or Santa Gertrudis are especially appropriate in subtropical environments. If replacement requirements for suitably adapted females are met and terminal crossing is feasible, then a Bos taurus breed can be used to optimize carcass and meat characteristics and increase market value of terminal cross slaughter progeny.
In developing composite populations with an overall level of 50% tropical adaptation, it may be appropriate to substitute a portion (e.g., 25%) of non Bos indicus germplasm for Bos indicus germplasm from such breeds as the Tuli, Romosinuano, or Senepole to maintain tropical adaptation and improve meat tenderness, provided they are crossed with other breeds that optimize size and growth rate. However, additional research is needed to determine optimum contributions of Bos indicus, British Bos taurus, Continental Bos taurus, tropically adapted Sanga breeds, and tropically adapted Criollo breeds from Central and South America in beef production in subtropical environments of the U.S.
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References |
| Cundiff, L. V., K. E. Gregory, and R. M. Koch. 1974. Effects of heterosis on reproduction in Hereford, Angus, and Shorthorn cattle. J. Anim. Sci. 38:711-727. |
| Green, R. D., L. V. Cundiff, G. E. Dickerson, and T. G. Jenkins. 1991. Output/input differences among non-pregnant, lactating Bos indicus-Bos taurus and Bos taurus-Bos taurus F1 cross cows. J. Anim. Sci. 69:3156-3166. |
| Gregory, K. E. and L. V. Cundiff. 1980. Crossbreeding in beef cattle: Evaluation of systems. J. Anim. Sci. 51:1224-1241. |
| Gregory, K. E., L.V. Cundiff, and R. M. Koch. 1999. Composite breeds to use heterosis and breed differences to improve efficiency of beef production. U.S. Department of Agriculture, Agricultural Research Service. Technical Bulletin 1875 pp. 1-75. |
| Jenkins, T. G., L. V. Cundiff, and C. L. Ferrell. 1991. Differences among breed crosses of cattle in the conversion of food energy to calf weight during the preweaning interval. J. Anim. Sci. 69:2762-2769. |
| National Pedigreed Livestock Council Annual Report, Directory, and Career Opportunities. 2002. pp. 1-20. |
| Olson, T. A., K. Euclides Filho, L.V. Cundiff, M. Koger, W.T. Butts, Jr., and K. E. Gregory. 1991. Effects of breed group by location interaction on crossbred cattle in Nebraska and Florida. J. Anim. Sci. 69:104-114. |
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Pinpoint Brangus
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Beef Sire Selection Manual
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U.S. Department of Agriculture
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