Abstract
Genetic correlations of heifer fertility and first-parity yield usually were negative and opposite in sign from genetic correlations of first-parity fertility and yield. Most estimates of genetic correlation between heifer and first-parity fertility were not significantly different from zero. Increasing yield may improve genetic potential for fertility, but stress of increased yield may overcome genetic potential for improved fertility. Days open and 305-day yield for first parity were considered with index selection; sires were evaluated on daughter performance. Days open had a small influence on the selection index; genetic gains in days open for first parity were largely offset by correlated losses in service period for heifers. Restricted index selection, holding days open constant, required considerable economic importance of days open.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 306-314 |
| Number of pages | 9 |
| Journal | Journal of Dairy Science |
| Volume | 66 |
| Issue number | 2 |
| DOIs | |
| State | Published - 1983 |
Bibliographical note
Funding Information:The authors acknowledge with gratitude the help of R. W. Everett, Cornell University, in matching breeding receipts and DHI production files. We also acknowledge the financial support of Eastern Artificial Insemination Cooperative, the National Association of Animal Breeders, and Grant 1-3-79 of the USA-Israel Binational Agricultural and Development Project.