Management of animal genetic resources for sustainable dairy production systems

The main stream dairy breeds suffer a continuous process of fertility and health decay, due to genetic antagonism with the high milk yield attained through the very successful selection for this trait, as food intake did not sufficiently increase to meet initial lactation requirements inducing negative energy balance. Selection for angularity (dairy form) aggravated the problem, because it resulted in lower body condition cows and inbreeding depression also concurs to the negative outcome. In addition, a negative genetic correlation between milk yield and heat tolerance has been shown in Holsteins. Correcting course seems sensible. However, given the present commercial structure, it seems unlikely that this may be effectively done by selection. Shifting to new breeds, such as the New Zealand Friesian and Jersey and the Norwegian and Swedish Red, might be preferable, particularly in the Latin-America context, where high yield systems are not prevalent and crossbreeding has proved profitable