Influence of genetic merit on reproductive performance of dairy cattle on commercial farms

Abstract

Reproductive performance has been reported to be declining within the UK dairy herd due to continued selection for increased milk production. The aim of the current work was to assess the influence of genetic merit for milk production (as described by PIN₉₅, the index in use at the time), and level of herd performance on reproductive performance. Fertility records from seven commercial dairy farms over a two-and-a-half year period between August 1997 and January 2000, providing a total of 1003 cow records (with a mean genetic merit of 38·6 (±0·80) PIN₉₅) were collected. The influence of genetic merit for milk production, herd mean 305-day milk yield and their interaction on the reproductive performance of individual dairy cattle was estimated. Additionally, 90-day milk yield, 90-day body condition score and deviation from herd mean 305-day milk yield were also investigated for their influence on fertility. A series of regression models using the Proc GLM procedure in SAS were run using data from those cows that conceived during the monitoring period (n=874) (PIN₉₅=38·8±0·83). The models included the variables, year of calving, month of calving and parity. The results showed that days from calving to conception and services per conception increased significantly both with herd 305-day milk yield, and within herds with deviation from herd 305-day milk yield level. Calving to conception also increased with reduced body condition score of cows at 90 days postpartum. Genetic merit (PIN₉₅) was not significantly related to these fertility measurements.