^^^/Jy^ Ag84Te Composite Breeds To Use United States Department of Heterosis and Breed Agriculture Agricultural Differences To Improve Research Service Efficiency of Beef Production Technical Number 1875 If) cooperatJon with the Institute of October 1999 Agriculturs and Natural Resources, University of Nebraska-Lincoln United States Department of Agriculture Composite Breeds To Use Agricultural Heterosis and Breed Research Service Differences To Improve Technical Bulletin Number 1875 Efficiency of Beef Production October 1999 In cooperation with the Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln K.E. Gregory, LV. Cundiff, and R.M. Koch Gregory is a research geneticist and Cundiff a research leader, U.S. Depart- ment of Agriculture, Agricultural Research Service, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933. Koch is a professor emeritus. University of Nebraska, Department of Animal Science, Institute of Agriculture and Natural Resources, Lincoln, NE 68583-0908. Abstract Gregory, K.E., L.V. Cundiff, and R.M. Koch. 1999. While supplies last, single copies of this publication Composite Breeds To Use Heterosis and Breed may be obtained at no cost from Keith Gregory, Differences To Improve Efficiency of Beef Produc- USDA-ARS, Roman L. Hruska U.S. Meat Animal tion. U.S. Department of Agriculture Technical Research Center, P.O. Box 166, Clay Center, NE Bulletin No. 1875, 81 pp. 68933. This report is a summary of results from a long-term Copies of this publication may be purchased from experiment of 15 years conducted with beef cattle at the National Technical Information Service, 5285 the Roman L. Hruska U.S. Meat Animal Research Port Royal Road, Springfield, VA 22161; telephone Center. The study estimated the retention of hetero- 703-605-6000. sis for major bioeconomic traits in composite popu- The United States Department of Agriculture lations (established with contributions by four or (USDA) prohibits discrimination in all its programs five purebreeds) and evaluated the potential of using and activities on the basis of race, color, national these composite populations to achieve and maintain origin, gender, religion, age, disability, political optimum performance levels and to maintain high beliefs, sexual orientation, and marital or family levels of heterosis. At least 13 scientific papers were status. (Not all prohibited bases apply to all pro- published from this project, resulting in numerous grams.) Persons with disabilities who require alter- conclusions, presented here. native means for communication of program This publication will be of use to scientists, students, information (Braille, large print, audiotape, etc.) and extension specialists interested in beef cattle should contact USDA's TARGET Center at 202- breeding and genetics; beef cattle breeders; and 720-2600 (voice and TDD). others with interests in the beef cattle industry. To file a complaint of discrimination, write USDA, Keywords: beef cattle breeding, breed composition, Director, Office of Civil Rights, Room 326-W, breeding, calves, cattle, crossbreeding, composite Whitten Building, 14th and Independence Avenue, breeds, genetics, genotype, heritability, heterosis, SW, Washington, DC 20250-9410 or call 202-720- heterosis retention, heterozygosity, inbreeding, 5964 (voice or TDD). USDA is an equal opportunity phenotype provider and employer. Issued October 1999 Contents Executive summary iv Rationale for development of composite breeds iv Conclusions from experimental results iv Introduction 1 Experimental procedure 2 Populations 2 Mating procedure 5 Management of heifers and cows 6 Feeding of young heifers and young bulls 7 Data collection 7 Growth, feed efficiency, and carcass and meat data of castrate males 7 Analysis of data 9 Results and discussion 9 Heterosisand heterosis retention 9 Differences among parental breeds 23 Inbreeding coefficients 49 Genetic and phenotypic variances 49 Heritabilities 49 Genetic correlations 55 Phenotypic correlations 67 Adjustment factors for age of dam 67 Composite breed formation c 67 References 72 Glossary 73 111 Executive Summary Rationale for Development of Composite Breeds 7. Composite breeds offer the opportunity to (a) use high levels of heterosis on a continuing 1. Heterosis (hybrid vigor) for major bioeconomic basis if population size in seedstock herds is traits, including reproduction, calf survival, sufficiently large or if periodic introduction of maternal ability, growth rate, and longevity of new genetic material is made to avoid inbreed- beef cattle is important. Heterosis can be used to ing, (b) achieve and maintain optimum breed increase weight of calf weaned per cow exposed (additive genetic) composition needed to match to breeding by 20 percent. Crossbred cows performance characteristics of different compos- remain in the herd 1.3 yr longer and have a 30 ite breeds to each of a wide range of production percent greater lifetime production than straight- situations and to different market requirements, bred cows. and (c) achieve and maintain uniform perfor- mance levels from one generation to the next. 2. Large differences exist among breeds of beef cattle for major bioeconomic traits, including growth rate and size, composition of gain, milk Conclusions From Experimental Results production, dystocia (calving difficulty), age at puberty, and climatic and nutritive adaptability. 1. High levels of heterosis were observed for These are traits where the optimum is deter- growth rate, reproduction, and maternal traits, mined by production environment and by including milk production. market requirements. 2. Heterosis differed among composite populations 3. About 55 percent of the cows in the U.S. beef for some major bioeconomic traits. Results breeding herd are in units of 100 or fewer cows. suggest that specific cross heterosis is impor- This involves about 93 percent of the farms and tant, that is, the level of heterosis for traits may ranches that have beef cows. vary among breed crosses. 4. Crossbreeding systems can achieve high levels 3. Generally, retained heterosis in advanced of heterosis. However, optimum crossbreeding generations was equal to or greater than ex- systems are difficult to adapt in herds that use pected based on retained heterozygosity in the fewer than four bulls. three composite populations. 5. Fluctuation in breed composition between 4. Results suggest that although there is generally generations in rotation crossbreeding systems a high relationship between retained heterosis can result in considerable variation in level of and retained heterozygosity, the relationship is performance among cows and calves for major not linear for all situations, that is, for some bioeconomic traits unless breeds used in the traits and in some breed combinations, retained rotation are similar in performance characteris- heterosis may be greater or less than expected tics. based on retained heterozygosity. 6. Use of breeds with similar performance charac- 5. Even though results suggest that specific cross teristics restricts the use that can be made of heterosis is of some importance, it is not fea- breed differences to optimize average genetic sible to have estimates of F^ heterosis and of merit for major bioeconomic traits. This in- heterosis retained in advanced generations of a cludes traits such as growth rate and size, large number of specific breed combinations in carcass composition, milk yield, and age at order to choose breeds as contributors to spe- puberty. cific composite populations (breeds). Thus, the IV use of average values for F^ heterosis and of 10. Large differences among parental breeds were retained heterosis based on genetic expectation observed for growth rate and size; dystocia; age in advanced generations of inter se mated at puberty; scrotal circumference; maternal composite populations is suggested for Bos traits, including milk production; and carcass taurus breeds. composition. 6. These results, generally, support the hypothesis 11. Composites were generally intermediate to that heterosis in cattle can be accounted for by parental breeds for carcass composition and dominance effects of genes. Thus, heterosis in more nearly approached the optimum carcass breed crosses involving Bos taurus breeds can composition, for example, Hereford, Angus, and likely be accounted for by recovery of accumu- Red Poll (British breeds) had more carcass fat lated inbreeding depression that has occurred in than is optimum, whereas the continental breeds breeds since their formation. tended to have less carcass fat than is optimum to meet current market requirements in U.S. 7. Estimates of genetic standard deviations and beef production systems. phenotypic coefficients of variation were similar for parental purebreds combined and for com- 12. There is limited opportunity to select among or posite populations combined for most within breeds to achieve high levels of marbling bioeconomic traits. Estimates of heritability or high levels of fat in the longissimus muscle were similar for parental purebreds and compos- simultaneously with achieving a high percent- ites. Thus, no increase in genetic variation was age of retail product in the carcass. These results observed in composite populations relative to suggest that the most logical approach to resolu- contributing purebreeds. The similarity of tion of the genetic antagonism between favor- genetic variation for composites and contribut- able carcass composition and less favorable