Age Optimization of First Calving to Achieve the Best Reproductive Performance in Holstein Dairy Cattle

The objective of the present study was to investigate the associations between age at first calving and reproductive performance in Holstein dairy cattle. A total of 4655 reproductive records of Holstein dairy cattle collected between 2013–2018 were used to study the effect of age at first calving (AFC) on dry period (DP), days between calving and first service (CTFS), days open (DO), calving interval (CI), number of services per conception (NSC) and dystocia. Heifers were classified into five age groups based on the age of the first calving 20–22, 23–24, 25–26, 27–28 and 29–32 months, and subsequently, the effect of AFC classes on the studied traits was tested. The effects of AFC on DP, CI, DO, and CTFS were evaluated using the general linear model procedure. Also, a logistic procedure was used to investigate the effect of AFC on NSC and dystocia. Age at first calving significantly affected all the traits investigated except for DP and CTFS. The results of this study showed that decreased AFC led to improvement of reproductive trait. Also, AFC less than 23 months led to an increased incidence of dystocia. It is therefore recommended that the age of first calving should be between 23 and 24 months.