GENETIC AND PHENOTYPIC RELATIONSHIP BETWEEN REPRODUCTION AND MILK-PRODUCTION

Records of fertility and milk production of 7117 lactations of Israeli Friesian cows from kibbutzim in Israel were analyzed. The objectives were to investigate the additive genetic effect on reproduction and the phenotypic and genetic relationship between reproduction and milk production. Fertility traits were measured in the period prior to the lactation in which milk production was measured. The phenotypic relationship between days open and milk production traits in the succeeding lactation was positive. Abortions and retained placenta were associated with decreased milk and delayed conception. The genetic analysis was based on a minimum of 2, 10, or 50 cows per sire. Heritabilities of days open and fat-corrected milk per milking day were around .05 and .15. The genetic correlation between the two traits was .62 to .72. The regression of the breeding value of kilogram fat-corrected milk per milking day was approximately 7. © 1979, American Dairy Science Association. All rights reserved.