Selection of Dairy Cow Families For Superior Ferttility
The objective of this study was to determine if dairy cow families could be used to select for superior pregnancy rate. Holstein cow records in 13 southern states were obtained from Animal Improvement Laboratory of USDA. Cows were included from historical records dating back to birth year of 1981 or 1982 as the foundation cows. Historical records included cows calving and completing lactations through August, 2005. Cows from various generations were then put in maternal family groups using dam identification within herd. Standardized milk production and pregnancy rate (based on days open) deviations were obtained within herd-year-season. A family value was calculated by averaging the first and second lactations across parity by degree of relationship to the individual (free of progeny information) for generation one though four. Each family entered into one of three groups based on average deviations milk production, pregnancy rate, and combining pregnancy rate and milk into a selection index. Analysis was performed on fifth generation members to determine if milk production and pregnancy rates in the fifth generation were significantly associated with historical performance of the respective cow families. Average of the standardized values for milk production has improved (8,542 to 10,275 kg) from generation one to five while pregnancy rate decreased from (26.91 to 18.28) in the same period for cow families having daughters represented in the fifth generation. After adjustments for sire predicted transmitting ability (PTA), maternal-grandsire PTA, and family group for milk or pregnancy rate in the model the effect of maternal cow family remained highly significant for pregnancy rate (P < 0.05, R2=0.0759) and milk production (P < 0.05, R2=0.1192) when single trait selection was utilized. Utilizing a selection index with equal weights for milk and pregnancy rate the effect of the maternal cow family remained significant (P < 0.05, R2=0.0208) but pregnancy rate was not significant (P > 0.05, R2=0.0106). The findings provide evidence that pregnancy rate and milk production are inherited through the maternal lineage. Thus, there may be potential economic value in considering maternal family history for pregnancy rate when selecting future bull dams.
Advisor:Dr. Kevin Anderson; Dr. David Dickey; Dr. Gene J Eisen; Dr. Steven Washburn; Dr. Roger L McCraw
School:North Carolina State University
School Location:USA - North Carolina
Source Type:Master's Thesis
Keywords:animal science and poultry
Date of Publication:12/05/2008