Crossbreeding Dairy Cattle. III. First-Lactation Production

Abstract

The actual first-lactation yields of milk, milk fat, FCM, and per cent milk fat of 379 cows in the Illinois crossbreeding experiment were analyzed. Holstein and Guernsey bulls were bred to foundation cows of both breeds to produce Generation 1 crossbreds and purebreds. The F1 crossbreds were mated to sires of both pure breeds, after which a crisscrossing plan was followed. In addition, purebred groups were maintained each generation. There were significant additive genetic differences between the breeds in all generations, and the effect associated with breed of sire was larger than that for breed of dam. In Generation 1 the difference between crossbreds and purebreds was not statistically significant for any of the production traits. Orthogonal linear, quadratic, and cubic regressions were fitted to records for purebred and crossbred groups in Generations 2 and 3. Linear trends from Guernseys through the crossbreds to Holsteins were statistically significant, but neither of the other regressions approached significance. Thus, little evidence of heterosis from crossbreeding per se was found in Generations 1, 2, or 3. Interactions of sires of the same breed with the breeding of the dam were generally unimportant, except in Generation 3 where some inconclusive evidence of the specific combining ability was noted. Numerous significant differences in the general combining abilities of the various sires used were evident. © 1966, American Dairy Science Association. All rights reserved.