Crossbreeding for dairy production in the lowland tropics of Kenya - II. Prediction of performance of alternative crossbreeding strategies

The predicted performance of nine crossbreeding strategies for milk product ion and reproductive traits and cow live weights (LW) were compared. The st rategies were selected because of their superiority to many others. The dat a were from crosses of Ayrshire (A), Brown Swiss (B), Friesian (F) and Sahi wal (S) cattle. Performances were predicted from the results of a genetic m odel based on additive breed differences, dominance and additive x additive interaction effects for the breeds involved. The crossbreeding strategies were: first cross (F x S), two-breed rotation (AS)(Rot), three-breed rotati on (BFS)(Rot) and two- (F and S), three- (B, F and S) and four-breed synthe tic breeds based on equal and unequal contribution of the foundation breeds . The mean lactation milk yield (MY) of production systems based on F x S, (AS)(Rot) or (BFS)(Rot) cows and in which replacements are raised from with in, was also predicted under varying number of calvings (NL) and reproducti ve performance (RP). At the individual cow level, differences in the predic ted MY between the F x S cross, three-breed rotation and the synthetic bree ds were small. While the F x S cross was superior to the two-breed rotation for predicted MY, its performance was similar for MY expressed per unit of metabolic weight. Among the synthetic breeds, differences in MY expressed per unit metabolic weight were small. At the production system level, it wa s predicted that MY for production systems based on F x S cows become super ior to those based on (AS)(Rot) cows only at a NL higher than 4 and were in ferior to those based on (BFS)(Rot). This study shows that Fx S cows were c losely rivalled by the (BFS)(Rot) and the synthetics. Its inferiority was p articularly shown at the production system level. It is concluded that the first cross is not generally the best suited for dairy production systems i n the tropics. There is the need to promote greater awareness of the potent ial of synthetic breeds and to formulate strategies for developing and expl oiting them. (C) 2000 Elsevier Science B.V. All rights reserved.