Prospects For Enhancing Genetic Resistance to Disease in Dairy Cattle

Abstract

There is now substantial evidence that genetic selection in dairy cattle, soley for improved production, is associated with rising disease incidence. Diseases such as mastitis are multifactorial with complex etiology, which despite elaborate farm management schemes, costs the US dairy industry approximately $2 billion annually, and the Canadian industry between $500-700 million. Direct losses result from cow deaths, culling, milk discard, and antibiotic therapy of clinical disease. Although dollar losses from subclinical mastitis are much more difficult to estimate, these may be the most significant due to chronically reduced milk yields and altered milk composition of affected cows. Unfortunately, effective vaccines for the prevention of complex diseases such as mastitis, have not yet been realized. In addition, the relative lack of understanding of how genetic and physiological host factors influence immunological defense has hampered progress in the development of effective alternate preventatives. However, there is now evidence from numerous species that immune responsiveness and disease resistance are partly genetically regulated traits, and that enhancement of these traits based on genetic selection is feasible. In cattle, several genetic markers and immune response traits have been identified which have some association with mastitis or other economically relevant diseases, but these require confirmation in the context of breed and pertinent physiological status of the cow prior to use in selection schemes. Nonetheless genetic approaches to improve livestock performance and health hold great promise as environmentally sound alternatives to improved animal health, which at the same time should help alleviate concerns over the hazards and costs associated with conventional disease and production management.