Genetic Relationship Between Production and Breeding Efficiency

Breeding and production records of 10,-907 Holstein and 10,537 Guernsey lactations from Adohr Milk Farms, Camarillo, California, were analyzed, to determine the phenotypic and genetic parameters o£ milk and fat production and five measures of breeding efficiency.The five measures of breeding efficiency were: days open, calving interval, days from parturition to first breeding, days from first breeding to conception, and services per conception.The relationship between 120-day milk and fat production and breeding efficiency was essentially zero.Regressions of breeding efficiency on production indicated that breeding efficiency increased slightly as production increased.The regressions of breeding efficiency on age indicated that breeding efficiency increased slightly as cows got older.The herltability of breeding efficiency was low, approximately 0.05.Heritabilities of 120-day milk and fat production were 0.18 and 0.17 for Guernseys and 0.09 and 0.06 for Holsteins, respectively.Genetic correlations between ]20-day lactation production and breeding efficiency were significant and relatively large (approximately 0.50).Due to the low heritabilities of breeding efficiency, selection for breeding efficiency or lactation production would not change breeding efficiency materially.High production and reproductive efficiency are necessary for a cow to maintain a long, economically productive life.The measurement of this is universally accepted as the total units produced.Reproductive efficiency has many measures used with about equal frequency.Johansson (6) discussed fhe merits and dis-,o.dvantages of each measure.