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Tenure and Reasons for Disposal of Artificial Insemination Dairy Sires ^{1, 2,}

Department of Dairy Science, University of Florida Institute of Food and Agricultural Sciences, Gainesville

ABSTRACT

Completed life span records of 8,887 United States and Canadian sires of six dairy breeds leaving artificial service during 1939–1964 were analyzed. Over 36% were eliminated for reproductive inefficiency; characteristics or performance of offspring, 16%; disease 14%; problems of semen collection 12%; accident or injury 4%; and miscellaneons 18%. Heterogeneity in reasons for disposal was detected, indicating that frequencies of the different reasons for disposal varied among breeds, and were also changing within breeds over time.

Life span data were grouped into different periods to determine time trends. Average tenure increased from 1.74 years during 1940–1949 to 4.18 years during 1960–1964. Over-all tenure was 3.18 years. Breeds differed in average tenure: Ayrshires, 2.91 years; Brown Swiss, 3.46 years; Guernseys, 2.94 years; Holsteins, 3.40 years; Jerseys, 3.14 years; Milking Shorthorns, 2.90 years. Prediction equations for tenure were calculated for eaeh breed and time period by multiple covariance analyses. The pooled within-breed time period equation was = 3.95 – 0.1352 X + 0.0034 x² where is expected tenure in years and X is age at entry. For those sires which were not culled for undesirable characteristics of their daughters, tenure could be stated as = 4.14 – 0.2245 X + 0.0025 x². Tenure in the artificial insemination studs ranged up to 14.30 years and 28% of the sires were useful at 10 years or older.

¹ Florida Agricultural Experiment Stations Journal Series, no. 3063.

² The financial support of the National Association of Animal Breeders is gratefully acknowledged.