Genotype by environment interactions can result in bulls having different genetic merits applicable to different environments. Beef cattle have traditionally been finished on pasture in New Zealand. The desire to meet perceived market requirements for meat quality has encouraged progeny testing and led to feedlotting. The objectives of this study were to evaluate sires on the basis of performance of their pasture-finished steer progeny, their feedlot-finished steer progeny and to compare the assessments of these sires from offspring in each environment. Fourteen Angus sires had progeny in both environments comprising 54 pasture-finished steers and 148 feedlot-finished steers. Estimated Breeding Values (EBVs) of each sire were obtained separately for eight traits that were measured for both pasture and feedlot progeny. Product-moment correlations between sire EBVs based on pasture-finished progeny and EBVs based on feedlot-finished progeny averaged 0.11 (range -0.16 meat colour to 0.50 subcutaneous fat depth). The expected distributions of these correlations between EBVs were obtained by simulation for a range of null hypotheses determined by the true genetic correlation between performance in the two environments using Monte Carlo simulation. The expected distributions of correlations between environments were determined for differing numbers of progeny per sire and for the effect of preselecting prior to entering the progeny test. The distributions of correlations were used to determine whether the low observed correlations between EBVs estimated from each environment were likely to have arisen from chance sampling or were truly indicative of genotype by environment interaction. Based on actual progeny numbers per sire in each environment there were significant (P=0.05) sire by finishing environment interactions for most traits analysed. Increasing the number of progeny per sire would increase the chance of detecting such interactions, in that case separate progeny testing programmes for each environment may be necessary.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 192-195, 1997
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