Milk fat saturation and reproductive performance in dairy cattle

Unsaturated fatty acids (UFA) cannot be synthesized by mammalian cells due to a lack of desaturase enzymes. Combined with their limited supply to the small intestines, UFA have been proposed as nutraceuticals to ameliorate dairy cow fertility. However, field studies based on a large number of animals are lacking on this subject. Therefore the aim of the present study was to analyze a large dataset containing individual cow fertility records from dairy herds and link fertility key-performance-indicators like conception rate to first insemination (CRFI), days in milk to first insemination (DIMFI) and days in milk to conception (DIMCONC), to the level of UFA in bulk tank samples, the latter being a proxy for the dietary fatty acid profile on these herds. Within the two year study period, information from 15,055 lactations and 35,433 bulk tank milk samples was collected on 90 herds. The multilevel logistic regression model used, revealed a decreased CRFI on herds with a higher bulk tank UFA level. The decrease in CRFI was larger for higher producing herds. Increased bulk tank UFA was furthermore associated with higher DIMFI which, together with the lower CRFI, subsequently increased DIMCONC. Interestingly, higher variability in UFA, expressed by an increased coefficient of variation, was associated with an increased CRFI and decreased DIMFI and DIMCONC. In conclusion, the present study demonstrates that increasing the UFA content of milk should not be a goal as such when supplementing UFA to dairy cows as higher bulk tank UFA are associated with worsened fertility results.