Genetic and Phenotypic Relations of Milk Production and Postpartum Length with Health and Lactation Curve Traits by Lactation

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Abstract
Milk, including its components, is the most important trait for dairy cattle. The relationship of 26 other traits with milk production was quantified both genetically and phenotypically to investigate any unfavorable responses associated with increased production. Traits with antagonistic positive correlations with 305-day mature-equivalent milk production included postpartum length, locomotive cost and days dry. Postpartum length was calving interval or days in last lactation for terminal records. Traits with favorable negative correlations with milk production included culling rate, rate of decline in milk production per week, and mammary cost. Culling rate was a binomial variable defining whether a cow was eliminated from the herd during her lactation. Heritability of mature-equivalent milk production declined as lactation number increased: 0.27 .+-. 0.02 in 1st, 0.21 .+-. 0.02 in 2nd, 0.16 .+-. 0.02 in 3rd and 0.15 .+-. 0.02 in 4th lactation. The maximum heritability of postpartum length was 0.06 .+-. 0.01 in the 1st lactation. Heritabilities of culling rate and days dry were less than 0.05. More than 62,000 records of progeny of 323 sires were analyzed.
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