Theoretical and practical ways to improve meat and milk production in the tropics by selection within local Bos indicus breeds, within Bos taurus x Bos indi- cus composite populations, upgrading of Bos indicus with Bos taurus breeds and through different crossbreeding programs have been discussed by various authors and summarized by Mason and Buvanendran (1982), Gregory et al. (1982) and Hickman (1979). Only few publications (Auriol, 1984? Chacko et al., 1985; Donegan and Roberts, 1984) exist on successful programs but numerous reports in developing agencies (FAO, 1985; SDC, 1985) indicate that many possibilities have been exploited and that various breeding programs in the tropics resulted in a considerable improvement of meat and/or milk production. The problem is that many reports are based on small numbers of animals kept under various conditions and observed over a short period. Main reasons for the realized improvement are generally crossbreeding programs which combine the adaptability of Bos indicus breeds to harsh environments, the production potential of the Bos taurus breeds and lead to large heterosis effects characteristic for Bos taurus x Bos indicus crosses. The problem of the appropriate breeding policy, the optimum Bos taurus inheritance in tropical cattle populations, the suitability of different Bos taurus breeds to be crossed with local zebu breeds have been discussed in a large number of reports (FAO, 1984; FAO, 1985? SDC, 1985) and publications, for example Meyn and Wilkins (1974, 1975), Mason (1974), Cunningham (1979, 1981) Frisch and Vercoe (1982) , Hickman (1981) , Cartwright (1982) , Syrstad (1985) and many others. The main conclusion is that Bos taurus inheritance should not exceed 50 to 75 %. In other words, the existence of genotype x environment interactions is generally accepted. There is no consensus about breeding policies and merits of different Bos taurus breeds for crossbreeding programs in the tropics.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume IX. Breeding programs for dairy and beef cattle, water buffalo, sheep, and goats., , 165–176, 1986
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