Aspects of the genetics of bovine blood systems : linkage, heterosis, gene frequency and association with production traits

Data from two separate beef cattle herds, the University of Tennessee (UT) Plateau Experiment Station Angus herd and the Virginia Polytechnic Institute (VPI) and State University herd at Front Royal, Virginia, containing Angus, Shorthorns, and Herefords, were utilized to investigate some of the genetic aspects of bovine blood systems. Analyses for linkage revealed that genes responsible for blood groups are not located on the sex chromosome. Attempts to find linkage between genes responsible for the F-V and R'-S' blood systems proved inconclusive. Studies of heterozygosity in the UT Angus herd using combinations of double homozygotes and heterozygotes between the F-V and R'-S' blood systems found heterozygotes in most cases to have higher least-squares means for production traits than homozygotes. More significant differences (.003 < P < .10) were found between double homozygotes and heterozygotes when sire effects were removed from models than when sire effects were included, indicating that confounding of blood type and sire can be extreme. Gene frequency analyses revealed that random drift caused drastic changes in the frequency of blood type genes of the VPI herd as several significant Differences (P < .05 or P < .01) in gene frequencies between years were observed. Analyses of variance were performed on various body and weight production traits to determine if associations of these existed with blood types within a system or with combinations of blood types of two systems. The Z and J systems were found involved with the majority of the associations revealed in the VPI herd. The phenotypes Z0/Z0 and J0/J1 occurred most frequently. Numerously more associations were found in the analyses involving combinations of blood types of two systems than in analyses dealing with blood systems separately. The transferrin system and the R'-S' and F-V blood systems were found in the majority of associations in the UT herd. In a comparison of observed and expected heterozygosis of the F-V blood system in the VPI herd, significant differences (P < .05 or P < .005) were found in three of the seven years studied in Angus and in one of the seven years studied in Herefords. Expected values were almost always less than observed values, but the intensity of inbreeding was probably not sufficient to reduce the frequency of heterozygotes appreciably, if at all.