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Genetic evaluation of test day production traits and somatic cell scores
Abstract
Test day records of 104,153 first lactations of Holstein cows, initiated between 1989 and 1993, were used to estimate (co)variance components among milk, fat, and protein yields and somatic cell count, for test days across the first lactation. Total lactation yields of milk, fat, protein, adjusted for 305 days in milk and on mature equivalent basis, and monthly somatic cell counts of 71,750 cows were also used to estimate (co)variance components among the four traits. Test day somatic cell counts were transformed to the log$\sb2$ scale and assigned scores from 0 to 9.9 (SCS), and the arithmetic mean of the available test day SCS was used for 305 d. Each data set was divided into five subsets based on herd identifier. Two-trait analyses with an animal model were used in both cases. For test day records, age at first calving, class of days in milk, and herd-test date were used as fixed effects. For 305 d yields, fixed effects were age at calving and herd-year-season. Pooled estimates of heritabilities were.19,.19,.18, and.13, respectively for milk, fat, protein and SCS. Genetic correlations between milk and fat and milk and protein were.25 and.72, and between SCS and milk, fat, and protein yields were.24,.20 and.36, respectively. Pooled heritabilities for test day traits were small, from.09 for SCS to.13 for milk. Each test day yield was highly genetically correlated with the respective lactation trait, and adjacent yields were highly correlated across the lactation. Genetic correlations between milk in all test days and SCS in the first half of lactation were positive but small. Among test day milk and protein yields, all correlations were consistently positive and large. Genetic correlations between milk or protein yields for test days in mid-lactation and all test day fat yields were close to zero. Estimates from a repeatability model used only on SCS were.08 and.51 for heritability and repeatability, respectively.
Subject Area
Livestock|Genetics
Recommended Citation
Gadini, Claudia Helena, "Genetic evaluation of test day production traits and somatic cell scores" (1997). ETD collection for University of Nebraska-Lincoln. AAI9725122.
https://digitalcommons.unl.edu/dissertations/AAI9725122