Abstract:

Records of 384965 parturitions and milk and reproductive performance in subsequent production cycles of 114 526 Black-and-White Polish Holstein-Friesian cows were collected from the SYMLEK database. The animals represented the active population in Pomorze and Kujawy regions, first calved in 2000-2012, and were used or culled until the end of 2013. The GLM and FREQ procedures of the SAS package were used in the statistical calculations. Sex of the calf influenced milk and reproductive performance of Polish Holstein-Friesian dairy cows and the effect was more favourable after a female calf was born. The advantage in milk performance of the cows which gave birth to female calves at first calving may be of importance in modern dairy herds, considering the increasing availability of sexed semen. Significant but small (around 1%) differences in the sex ratio of calves born within factors such as cow’s age or production level in the previous lactation do not allow taking these factors into consideration when controlling the sex of the calves born.

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