ASSOCIATIONS OF THE BOVINE MAJOR HISTOCOMPATIBILITY COMPLEX DRB3 (BOLA-DRB3) ALLELES WITH OCCURRENCE OF DISEASE AND MILK SOMATIC-CELL SCOREIN CANADIAN DAIRY-CATTLE

Potential associations were investigated between bovine leucocyte anti gen (BoLA) alleles and occurrence of disease. Cows (Holstein n = 835; Jersey n = 66) were examined for polymorphisms of the second exon of t he BoLA-DRB3 gene, using the polymerase chain reaction (PCR), followed by digestion of the amplified fragments with three restriction endonu cleases. Disease occurrences were recorded for each cow throughout one lactation. Milk somatic cell count data were retrieved through the Da iry Herd Improvement records and converted to somatic cell score (SCS) . There were no effects of BoLA alleles on SCS in Jersey cows, but BoL A-DRB3.2(star)16 was significantly associated (P less than or equal to 0.05) with lower SCS in Holsteins. Since the number of Jerseys was re latively small and prevalence of diseases in this population was low, health records of Jerseys were not analyzed further. BoLA associations with occurrence of disease in Holsteins were investigated using a log -linear model. There was a significant (P less than or equal to 0.05) association between BoLA-DRB3.2(star)23 and occurrence of severe masti tis, from which coliforms were the most commonly isolated bacteria. Th e BoLA allele (star)3 was associated with a lower risk of retained pla centa (P less than or equal to 0.05) and alleles (star)6 (P less than or equal to 0.05) and (star)22 (P less than or equal to 0.05) with a l ower risk of cystic ovarian disease. Although more studies are require d to confirm the present findings, it can be concluded that BoLA allel es may have potential usefulness as genetic markers of higher or lower risk of disease occurrence in cows.