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Life Span and Livability of Crossbred Dairy Cattle^{1, 2,}

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

ABSTRACT

Records of lifetime reproductive performance on a population of over 1,000 cows were provided by a cooperating Florida institutional dairy herd for the years 1939–64. All animals had freshened one or more times. About 85% were straightbred Jerseys (registered or grade) or Holsteins, 7% Jersey-Holstein crosses, and 8% Jersey-Guernsey crosses of various order. Registered Jerseys were not used for cross-breeding; tests of heterosis involved only the grade Jerseys and Holsteins and their crosses. About 88% of all cows were culled for reasons suggesting an innate weakness in livability, but no evidence of heterosis was detected. Average age at first calving of all cows was 28.8 months; productive life span, 42.4 months; total life span, 71.2 months; parturitions, 3.5. Jerseys differed significantly from Holsteins for these traits by +1.9, +9.9, and +10.7 months, and +0.7 parturitions, respectively. Jersey-Holstein crosses performed at levels suggesting lack of heterosis. Performance of Jersey-Guernsey crosses was consistently poorer than that of Jerseys, Holsteins, or their crosses. Other findings included: Abortion rates of crossbreds and straightbreds were 5.3 and 3.5%, respectively, differing at P < 0.05; twinning rates were 1.4 and 1.6% (not significantly different). The apparent lack of heterosis in livability and life span of cattle after freshening suggested that dairymen hoping to make improvements in these traits by crossbreeding would be disappointed.

¹ Florida Agricultural Experiment Stations Journal Series, no. 2397.

² Support for Miss Curl by the National Science Foundation Science Summer Research Participation Program is gratefully acknowledged.

³ Department of Agricultural Economics.