Relationship between reproductive management practices and fertility in primiparous and multiparous dairy cows.

The aim of this study was to analyze the impact of reproductive management practices on fertility in primiparous and multiparous dairy cows and to identify the differences by parity. Data on reproductive performance and management of cows were gathered from 34 large commercial Holstein-Friesian dairy herds in Hungary. Individual data on 23 781 cows that calved in the studied herds in 2014 were collected from the national milk recording database and used to calculate the reproductive indices. Farm managers and veterinarians were interviewed in person from May 22 to November 6, 2015 using a questionnaire to collect information about reproductive management practices. The data were statistically analyzed by mixed-effects models. Our results showed that the use of a voluntary waiting period (VWP) was linked to a greater increase in calving-to-conception interval (CCI, P < 0.05) and a greater decline in the chance of pregnancy at 200 days in milk (P200, P < 0.001) in multiparous cows. Estrus synchronization was related to a larger reduction in days-to-first service (DFS, P < 0.001), breeding interval (IBI, P < 0.05), and CCI (P < 0.01) and a greater improvement in P200 (P < 0.001) in primiparous cows. Early pregnancy diagnosis and pregnancy recheck improved IBI (P < 0.01 for both practices), CCI (P < 0.01 and P < 0.001, respectively), and P200 (P < 0.001 for both practices) to a larger extent in primiparous than in multiparous cows. In conclusion, estrus synchronization, early pregnancy diagnosis, and pregnancy recheck led to a greater improvement in fertility in primiparous cows than in multiparous cows.