Heritability and Repeatability of Fertility of Dairy Sires

Heritabilities and repeatabilities were derived from nonreturn data of young sires in the sire sampling program and of the proven sires in the Eastern Artificial Insemination Cooperative, Inc., 1965 through 1974. Effects of season and time were minimized by deviation of monthly nonreturn rate for each sire from the monthly average of his contemporary group. The weighted average of deviations was the fertility rating. Heritabilities from half-sibs were for young sires .21 on 274 sons, .22 on 252 sons, for proven sires .35 and 28 sires (liquid semen), and from regression of son on sire .20 on 161 pairs. Repeatability was .12 on 34 sires which had fertility ratings with frozen semen as young sires and as proven sires. There was considerable selection of sires when frozen semen was from proven sires. Some sires had only 12% of their services to cows in Dairy Herd Improvement Associations while others had as high as 51%. Where random-like service exists as in a well-designed young-sire-sampling program, genetic differences among sires in nonreturns can be discerned.