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Use of records of bovine somatotropin treated cows in genetic evaluation
Abstract
Predicted breeding values (PBV) for dairy cattle may be biased when DHI records of bST-treated cows are used in genetic evaluations. Test-day records and 305-d lactation records of 12,745 Holstein cows obtained from the North Carolina State Dairy Records Processing Center were used to estimate the effects of bST and to predict breeding values on milk production traits and somatic cell score (SCS). Average percentages of increase due to bST treatment in the latter part of lactation were 3.9, 4.8, 4.0, and 2.9 for milk, fat, protein, and SCS, respectively. These differences increased with the number of postpartum days after the peak or middle of lactation. To assess the potential for bias in genetic evaluations, breeding values for milk, fat, and protein yields and SCS were predicted and compared using a 305-d lactation model and test-day models with and without adjusting for effects of bST. Correlations between PBV for 305-d lactation records adjusted and unadjusted for bST were ranging from.996 to.999 for the top 2% of cows and the top 10% of sires. These results suggest that bias of PBV due to ignoring bST treatment or genotype by bST interaction might be small. Correlations between PBV from a 305-d lactation model and a test-day model which defined the lactation curve by each season were higher than for other models for any production trait. Test-day records of 1503 Holstein cows in second lactation were used to investigate the influence of bST treatment in first lactation on lactating cows in second lactation. The effects of bST on milk, fat, and protein yields, and SCS were estimated using a test-day model. Cows receiving bST in the first lactation produced less milk and protein in the second lactation than cows not receiving bST in the first lactation, although most of the contrasts were not statistically significant. Cows receiving bST in the first lactation had lower SCS in second lactation than the other cows with some significant differences.
Subject Area
Genetics|Biostatistics|Livestock
Recommended Citation
Tsuruta, Shogo, "Use of records of bovine somatotropin treated cows in genetic evaluation" (1998). ETD collection for University of Nebraska-Lincoln. AAI9902979.
https://digitalcommons.unl.edu/dissertations/AAI9902979