Fertility subindex for improving fertility performance in Iranian Holstein cows.

Different fertility indices were constructed for improving fertility performance in Iranian Holstein dairy cows. Number of inseminations per conception and days from calving to first insemination, each weighted by its economic value, were included as breeding goals in the aggregate genotype definition. Different fertility indices (FI) were constructed with different combinations of available fertility traits: number of inseminations to conception (INS), days from calving to first service (DFS), interval between first and last insemination (IFL), and days open (DO). The fertility index (FI1) that included INS and DFS had the greatest genetic gain for INS (-0.39 insemination), DFS (-7.47 days), and profit ($4.3) per generation. Genetic gain for profit, DFS, and INS including only DO showed slight differences regarding FI1. A selection index that included only INS (DFS) presented the larger (smaller) genetic gains for INS and smaller (larger) for DFS, which were -0.40 (-0.034) and -0.975 (-11.18) inseminations and days, respectively. The result of this study showed that recording INS and DFS are preferable traits for including in a fertility subindex. DO can be used in the absence of other fertility traits.