Effects of Serum Treated Semen, Bulls, and Herdsmen-Inseminators on Conception to First Service in Large Commercial Dairy Herds

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Abstract
Semen from each of 10 Holstein bulls was extended to 15 .times. 106 total spermatozoa per dose in egg yolk-Tris and in egg yolk-Tris containing 20% (vol[volume]/vol) heat-treated heifer serum. Semen was used for 12 mo. by 11 herdsmen-inseminators in 4 commercial dairy herds to inseminate 2820 Holstein cows on the 1st postpartum service. Percentage conception of cows free of clinical disorders at breeding was determined by rectal palpation at 30-60 days after insemination. Addition of serum to the extender did not influence percentage conception. A significant interaction of bull .times. seminal treatment was found. Least squares means of percentage conception to 1st service ranged from 45.3-59.9% among the 10 bulls. When bulls were classified as either high (> 55%), average (50-55%), or low conception (< 50%), approximately 200 first services were required to classify correctly 80-90% of the bulls. Least squares means of conception rates ranged from 40.1-62.7% among the 11 herdsmen-inseminators. Addition of heat-treated homologous heifer serum to the extender does not influence conception in a predictable fashion; fertility inherent to the bull significantly influences conception; and inseminator skill affects conception greatly.