Type, Body Size and Breeding Efficiency of Ayrshire Cow Families

Summary Data on type, body size, breeding efficiency and length of service period of 19 cow families were analyzed by the analysis of variance. Estimates of the variance components were obtained by equating the sample values to the expected sums of squares. The family averages for weight, breeding efficiency and length of service period varied considerably. These differences were not significant, however, with 0 -2 f accounting for only a small portion of the total variation. The significant differences between families for type and height at withers could be partially attributed to environment and to the sires that were used on these cow families. Except for wither height, the sire variance was somewhat larger than that attributed to the family influence. The error variance explained more than half the total variation in every characteristic studied. The low relationship between members of the same cow family may account for the small amount of variance attributed to family differences. It appears that under present breeding practices the genetic variance between families is too small for family selection of type, body size and breeding efficiency to be very effective.