Impact of the fatty acids in the diet on milk fat content: analysis from a database of commercial farms
Controlled trials have shown that milk fat content can be affected by dietary fatty acids. The purpose of this study was to evaluate the impact of dietary fatty acids on milk fat content in commercial dairy herds using multiple regression procedure. Data recorded by Valacta (Dairy Center of Expertise, Québec-Atlantic) from 2009 to 2011 were used for the analysis. The fatty acid content in feed ingredients (16:0, 16:1, 18:0, cis 18:1, trans 18:1, 18:2 and 18:3), not originally in the database, were obtained from CNCPS V6.1, INRA Tables of Feed Composition, and peer-reviewed articles. Test-day records from Holstein cows in early- (1-50 DIM) and peak- (51-100 DIM) lactation during winter months were used, giving 2,491 records over the 3-yr period from 1,585 cows and 143 herds. Statistical analyses were performed using the MIXED procedure of SAS with herd and cows(herd) as random effects. Independent variables were included in the final equation when P ≤ 0.10. The variables used as covariates in the regression were DIM and estimated breeding value for fat composition (EBV_FAT). Variables tested to explain milk fat concentration were: forage NDF + 0.5 × concentrate NDF content (NDF_NRC), NFC content, buffer intake (BUFF), and intake of previously listed individual fatty acids. Multiple regressions for data from early lactation records (n=390; R2=0.43) included, in addition to the covariates, the variables 18:0 (quadratic), cis 18:1 (quadratic), 18:2, and BUFF. For peak-lactation records (n=422; R2=0.49) the variables included were 16:0 (quadratic), 16:1, 18:0 (quadratic), trans18:1 (quadratic), 18:2 (quadratic), NFC (quadratic), NDF_NRC (quadratic), and BUFF. The nonlinear relationships observed for several fatty acids retained in the model could be explained by the heterogeneity of fatty acid sources on commercial farms (forages, cereal grains, oil seeds, fat supplements in the form of triglycerides, free fatty acids or calcium salts, etc.), and their interaction with numerous feed ingredients. The current study gives insight into the relationships between individual dietary fatty acids and milk fat content in the context of commercial milk production.
Keywords: Dietary Fatty Acids, Milk Fat, Lactating Dairy Cows