2 RETROVIRAL INFECTIONS OF PERIPARTURIENT HOLSTEIN CATTLE - A PHENOTYPIC AND GENETIC-STUDY

Environmental and genetic factors affecting prevalences of antibodies to bovine leukosis virus and bovine immunodeficiency-like virus were s tudied on 137 periparturient Holstein cows selected for milk productio n. Environmental effects were obtained by logistic regression, and gen etic parameters were determined using threshold animal models. Cows se lected for high predicted transmitting ability for kilograms of milk f at plus protein had the highest prevalence of antibodies to bovine imm unodeficiency-like virus and the lowest prevalence of antibodies to bo vine leukosis virus. Heritability estimates for susceptibility to retr oviral infections were close to zero.