Heritabilities and Correlations of Lactation Yields and Fertility for Holsteins

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Abstract
First lactations from a total of 5802 cows in the North Carolina Institutional Breeding project [USA] from 1950-1980 were used. Heritabilities from paternal half-sisters were 0.05 for days open, 0.05 for age at 1st calving, 0.27 for lactation milk yield and 0.29 for fat yield. Corresponding estimates from regressions of cow on dam were 0.13 for days open, 0.06 for age at 1st calving, 0.35 for milk yield and 0.33 for fat yield. Genetic correlations between yields and days open from various methods of estimation and editings of the data were all antagonistic and ranged from 0.35-0.60. Genetic correlations of yield and age at 1st calving were favorable, ranging from -0.10 to -0.36. Heritabilities for days open and genetic antagonism between days open and yield were greater for cows calving prior to the hot summer months than for cows calving in the fall. Heritabilities and variance of sires increased for days open and yield traits from the 1950-1980. For records from 1970-1980, heritability from paternal half-sisters of days open was 0.12. Genetic increase of 1000 kg milk would result in 5-10 additional days open.

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