Phenotypic, Genetic, and Environmental Relationships of Milk Production and Type Ratings of Holstein Cows

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Abstract
Data from 233 Holstein cows with 671 lactation records and 2272 classification scores from the New Jersey Agricultural Experiment Station were analyzed. Milk records were adjusted to a 2X, 305-day M.E. basis; type scores were adjusted for the effects of age, season, stage of lactation, classifier and year. Repeatability of single lactation records for milk yield, 4% FCM yield and fat yield ranged from 0.53 to 0.56, with an estimate of 0.75 for fat percentage. Heritabilities of single records for the 3 measures of yield were 0.12 to 0.14, and for fat percentage, 0.69. Heritability estimates for the average number of records per cow (2.88), and for an infinite number of records per cow, were also calculated. Repeatability of type scores based on a single classification ranged from 0.24 to 0.56, with heritabilities ranging from 0.09 to 0.27. Phenotypic, genetic and environmental correlations were calculated from components of variance and covariance for all combinations of variables. Phenotypic correlations between over-all rating and measures of yield ranged from 0.13 to 0.15; between subratings and yield, from 0.18 to 0.20 for dairy character to 0.05 to 0.07 for rump. Correlations between fat percentage and type were essentially zero. Environmental correlations between type and measures of yield were positive and ranged from 0.05 to 0.21. Genetic correlations were also positive but low; the highest was 0.26 between fat yield and dairy character. Genetic correlations among type scores ranged from -0.02 to +1.11. Among measures of milk production the following genetic correlations were obtained: milk yield with 4% FCM yield 0.78, with fat yield 0.74, and with fat percentage -0.02; 4% FCM yield with fat yield 0.96, with fat percentage 0.13; fat yield with fat percentage 0.21. Moderately low heritabilities and low genetic correlations between measures of type and production indicated that relatively little progress can be expected in the improvement of milk production due to selection for type.