Repeat breeding (RB) has been defined as failure to conceive from three or more regularly spaced services in the absence of detectable abnormalities, and cause economic loss on the farm owing to a declining conception rate. This study aimed to evaluate the reproductive characteristics of RB in Japanese Black cattle by assessing the longitudinal effect of RB at a low parity on subsequent fertility raised in commercial cow-calf operations. Data used in this study were collected from 764 farms in Miyazaki. Data from 2005 until 2014 comprised 158,945 AI records with 80,453 parity records for 22,565 cows. The effect of RB at heifers and parities 1 and 2 cows on subsequent fertility and survival on four consecutive parities was investigated. The results showed that cows with the number of inseminations to conception (INS) of ≥4 at a low parity had a higher probability of being RB again at subsequent parities compared with cattle with INS 1 or 2. Additionally, the degree of the negative effect of an INS ≥4 on fertility and survival increased as they became older. On the other hand, cows with an INS of 2 had similar fertility and survival with those with an INS of 1. In summary, this study suggests that repeat breeders at a low parity have a higher probability of RB again at subsequent parities compared with cattle with INS 1 or 2, and the negative effect of an INS ≥4 increases as parity increases.
Keywords: Culling rate; Infertility rate; Japanese black cattle; Number of inseminations to conception; Repeat breeder.
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