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Type Differences and Blood Antigens in a Guernsey Herd¹

ABSTRACT

The original data of this study were the records of a Guernsey herd over a period of 9 yr., during which an inbreeding program had been followed The pedigrees were examined as complete herd pedigree maps, as pedigree maps of the descendants of the main sires and as pedigree maps of cow families. Only slight and irregular differentiation into separate lines had taken place.

Many of the animals had been scored for the following thirteen characters: shoulders, neck, legs, barrel, tailhead, rump, loin, back, skin, ribs, fore udder, rear udder and teats. The presence or absence of some forty blood antigens had been recorded. The main object of this investigation was to determine whether any of the scores for, type were influenced by the presence of the various antigens.

The regression coefficients of score on inbreeding hint at slightly decreasing desirability of the character with increasing inbreeding. The half-sib correlations indicated heritability to be high for ribs, fore udder and teats. The scores in these three characters were adjusted by least squares analyses to remove the effects of variations in time of classification, in age and in inbreeding. Using these corrected scores, the intrasire regressions of daughters on dam indicated the heritability of these three characters to be between 0.34 and 0.50.

The eleven antigens which had zygotic frequencies nearest to 0.5 were selected as being most likely to demonstrate their effects, if any, on the three selected type scores. In only one of 33 analyses did the difference between the mean of the scores of those animals possessing the antigen and the mean of those not possessing it reach the 0.05 level of significance, although seven other differences approached this level. The average F value in these analyses was 1.80. This mean F value may indicate that some of the antigens do have real, though small, effects on some of the type scores, although other interpretations are not excluded. The only tenable genetic explanation of such joint effects seems to be pleiotropy of the genes controlling the antigens. Where genes at many loci control the expression of a continuous character, the correlation between the presence of an antigen, controlled by genes at only one of those loci, and the continuous character is unlikely to be large.

¹ Journal paper J-1818 from the Iowa Agricultural Experiment Station, Ames. Project 1053.

² Now Research Officer, Commonwealth Scientific and Industrial Research Organization, Sydney, N.S.W., Australia.