Genotype X environment interactions in dairy cattle: a New Zealand perspective

Abstract

AbstractIn recent genotype X environment studies between New Zealand and Canada, yields of fat and protein from Holstein Friesian (HF) cows were similar for daughters of sires from both countries, but Canadian daughters produced larger volumes of milk (6500 kg v. 3300 kg) and were taller. There was no interaction between the sire's national strain and the daughter's environment but there was a significant interaction between-individual sires within-strain and the daughter's environment so that the correlations between the sire proofs in the two countries were approximately half of the expected values.In New Zealand, milk production by cows of high or low genetic merit has been found to be affected similarly by differences in stocking rate, level of feeding and body condition at calving, providing no evidence of a large genotype X management interaction, although there is some evidence of an interaction between the effects of breed size and feeding, with smaller breeds being affected less severely by lower feeding level and clear evidence of genotype by milking management interactions. Over the past 40 years the need for pre-milking stimulation in New Zealand cows has been reduced or eliminated by inadvertent selection. Other recent evidence suggests that progress for genetic tolerance to once-daily milking may be possible.It can be concluded that interactions between group-average genotype and nutritional environment are not likely to have important effects on milk solid yields, at least within the HF breed, within the range of conditions normally found in temperate dairy systems, and provided that the environment is imposed from birth. However, there are likely to be significant interactions between the genotype of individual sires and environment and thus appropriate assessment and ranking of sires in each environment is essential.