COMPARISON OF SUMMARIZED SIRES AND SAMPLING SIRES IN ARTIFICIAL-INSEMINATION .1. PRODUCTION AND REPRODUCTION

A breeding project was initiated in 19 state-owned Holstein herds in Pennsylvania to determine the differences in reproduction and production traits between daughters of summarized sires and sampling sires available from AI organization. Each herd was divided randomly into two groups; females in one group were bred to summarized sires, and females in the other group were bred to sampling sires. First service conception rates were similar for the two groups of sires (46.3% for summarized and 45.6% for sampling sires). Services needed to produce a milking daughter averaged 6.65. There were no significant differences between the two groups of females for any of the reproductive or management factors studied. Although not significantly different, lactational yields tended to be higher for daughters of summarized versus sampling sires. The summarized sires used in the project were of higher transmitting ability for production traits than the average of summarized AI sires and the sampling sires were about average of all sampling sires at the time of use. Breeding group differences in first generation daughter yields were similar to sire transmitting ability differences.