Effect of Herd Environment on the Genetic and Phenotypic Relationships Among Milk Yield, Fertility, and Somatic Cell Score in Holstein...
- ISBN-10
- 0591924161
- ISBN-13
- 9780591924169
- Pages
- 135
- Language
- English
- Published
- 1998
- Author
- Hector Juarez Castillo
Description
A total of 248,230 first parity records of Holstein cows calving from 1987 to 1994, daughters of 588 sires in 3,042 herds were used to evaluate genotype by environment interactions in mature equivalent milk yield (MEM), lactation mean somatic cell score (LMSCS), and conception rate at first service (CRFS). Herds were classified into low and high management groups using three different criteria to differentiate production environments. Phenotypic means for MEM and body weight at first calving were greater in high than in low management herds, while low management herds had higher phenotypic means for LMSCS, CRFS, and age at first calving than high management herds. Genetic parameters were modeled using multiple trait linear models. For the complete data set heritability estimates for MEM, LMSCS, and CRFS, were 0.276, 0.103, and 0.015. Heritabilities and genetic and phenotypic correlations were consistent regardless of the environmental classification criteria. For low management herds, heritabilities for MEM, LMSCS, and CRFS averaged 0.232, 0.101, and 0.020, while for high management herds average heritabilities were 0.283, 0.097, and 0.009. For the low management herds, genetic (and phenotypic) correlations between MEM and LMSCS, MEM and CRFS, LMSCS and CRFS averaged 0.247, $-$0.407, and $-$0.228, ($-$0.055, $-$0.174, and $-$0.037), while for the high management herds they averaged 0.178, $-$0.304, and $-$0.139, ($-$0.089, $-$0.171, and $-$0.034). The genetic correlations between pairs of traits were consistently lower in high than in low management groups, suggesting a genotype by environment interaction. These changes suggest that differences of management between the two management levels reduces considerably the antagonistic genetic association between the traits studied. Breeding programs designed to increase milk yield at the same time that to reduce the genetic increase of LMSCS and the rate of genetic deterioration of CRFS must take into account the magnitude of the differences in the expected correlated responses in LMSCS and CRFS in the two levels of management.
