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Genetic Aspects of Milk Yield and Reproductive Performance¹

Department of Animal Science, Iowa State University, Ames 50011

ABSTRACT

The genetic relationship between milk yield and reproductive performance was investigated in 72,187 records with breeding information from 201 California dairy herds. Traits characterizing reproductive performance were days to first and last breeding, days open, and number of services; their heritabilities in primaparous cows were 4, 4, 2, and 1. Genetic correlations between reproductive performance and 60-day, 180-day, and 305-day fat-corrected-milk-yields were positive, indicating that higher producing cows were bred later, took longer to conceive, and required more services per conception. Genetic correlations were highest between measures of reproductive performance and 305-day yield but were less for the 180-day and 60-day yields which were unaffected by pregnancy.

¹ Journal Paper No. J-9633 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 1053.

² Department of Dairy Science, University of Illinois, Urbana 61801.

³ Department of Animal Science, University of California, Davis 95616.

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