Genetic selection programs for resistance to mastitis.

INTRODUCTION Interactions. Occurrence of disease results from an interaction of host, environment, and agent (Martin et al., 1994). An increase in the incidence of disease occurs around parturition (van Dorp et al., 1999) during which the immune system is impaired (Preisler et al., 2000). Recording of visible disease of different etiologies, i.e., environmental, contagious, metabolic, and trauma are usually grouped under one main heading, such as clinical mastitis (CM).