Perspectivas da avaliação genética multirracial em bovinos no Brasil

Abstract

Availability of large numbers of records from purebred and crossbred animals in cattle organizations, and increased demand from producers to have genetic predictions for both purebred and crossbred animals has renewed interest in the implementation of multibreed genetic evaluation procedures. Multibreed genetic evaluation procedures are currently used for the genetic evaluation of purebred and crossbred animals in most US breed associations. Brazil with its enormous cattle population (167 million), composed largely of Zebu and Zebu crossbreds (80%), and many well-organized large size cattle operations (many with 10,000 cattle or more) is likely to have a substantial number of datasets amenable to be analyzed using multibreed genetic evaluation procedures. Currently, however, only intrabreed genetic evaluation procedures are used in Brazil regardless of the breed composition of cattle populations. Intrabreed procedures ignore interbreed nonadditive genetic effects, and assume that genetic parameters are the same in all breed groups. Multibreed genetic evaluation procedures account for both aspects, thus they should be preferred to intrabreed procedures to genetically evaluate populations composed of purebred and crossbred animals. Multibreed genetic evaluation procedures yield more accurate additive genetic predictions, permit direct comparison of animals of different breed composition, and allow additive and nonadditive genetic improvement in multibreed populations. However, they are more complex computationally, require larger number of genetic parameters, and have problems of confounding and multicollinearity. Here, multibreed populations are characterized, genetic evaluation models, procedures, and implementation issues are discussed, and general comments relative to the Brazilian multibreed situation are made when relevant.