A1 and A2 are allotypes of bovine IgG2a which differ significantly in their primary structure, allotope expression and the products of pepsin digestion. An analysis of 754 beef cows from 14 different breeds at the Meat Animal Research Center (MARC), Clay Center, NE, demonstrated a significant difference in the distribution of A1 and A2 among breeds but failed to find any correlation between the clinical disease history of the animals tested and their A-allotype. The proportion of all animals with either a history of infectious or respiratory disease (43.3 ± 3.5 and 17 ± 0, respectively) was the same among A1 A1, A1 A2 and A2 A2 animals. Similarly, there was no preferential association between allotype and clinical disease within any one breed. A very high incidence of A1 homozygotes was found among Angus (84%), Brown Swiss (100%), Limousin (87%), MARC I (87%) and Pinzgauers (88%). In contrast, Herefords had a high incidence of A2 A2 homozygotes (41%) as did Brahmans (46%) and Gelbveih (34%). The distribution of A1 A1, A1 A2 and A2 A2 animals within any breed was totally consistent with the concept that A1 and A2 represent Mendelian co-dominant alleles. These data suggest that, among vaccinated female beef cattle in a normal environment, A-allotypy plays no role in the propensity for clinical disease as defined in this study. It does not rule out such an association in non-vaccinated, severely stressed animals and in calves exposed to severe outbreaks of an infectious agent.
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