Genetic correlations among female fertility, 305-day milk yield and persistency during the first three lactations of Japanese Holstein cows

The genetic correlations between reproductive traits in cows and milk-production traits (305-day milk yield and lactation persistency) were estimated by using first-lactation records (representing 476,284 Japanese Holstein cows), second-lactation records (380,474 cows), and third-lactation records (267,344 cows). The reproductive traits evaluated were: days from calving to the first insemination (DCF); conception rate for the first insemination (CR); number of inseminations (NI); and days open (DO). Persistency was defined as the difference between milk yields at 240 and 60 days in milk. Genetic parameters for reproductive traits (DCF, CR, NI, and DO) were estimated within each lactation by using a four-trait animal model. The genetic correlations between reproductive traits and milkproduction traits were estimated by using a three-trait (one reproductive trait and two milk production traits) linear model. The genetic correlation estimates within the first lactation were similar to those of the other lactations, suggesting that the genetic relationships among fertility, 305-day milk yield, and lactation persistency were constant over the first three lactations. The genetic correlations among reproductive traits were fairly strong, but those of DCF with CR and NI were relatively weak. Antagonistic genetic correlations, which ranged from 0.17 to 0.39 in absolute value, between reproductive traits and persistency were revealed. Therefore, when selecting to increase lactation persistency, indicators of female fertility have to be included in the genetic evaluation to reduce undesirable side effects on fertility in cows. (C) 2014 Elsevier B.V. All rights reserved.