Fernando Díaz, Juan Sánchez-Duarte, and Alvaro Garcia
This work has been accepted for the 2020 Annual Meeting of the American Dairy Science Association, West Palm Beach, Florida, June 21-24.
Linoleic acid (C18:2) is an unsaturated fatty acid commonly found in dairy ration feed ingredients that may inhibit milk fat synthesis. The objective of this study was to evaluate the effects of dietary C18:2 intake on lactating dairy cow performance. Sixteen trials that added corn (0.7-2.8% of DM) or soybean oil (0.5-7.4% DM) to the diet in 14 published articles (2000-2019) were included.
A mixed model meta-analysis was conducted using the random effect of study weighing by the inverse of the standard error of the means squared. Intakes of oleic (C18:1), linolenic (C18:3), rumen unsaturated fatty acids load (RUFAL), and all possible two-way interactions and quadratic effects were included in the models. Multicollinearity was quantified with the variance inflation factor (VIF). The best-fit model was chosen based on the lowest Akaike information criterion (AIC) and Root mean square error (RMSE). Residual vs. fitted values and Q-Q plots were used to identify the heteroscedasticity and normality of the final models, respectively. Marginal and conditional R2 explained the variance of the final models. No interactions, but high multicollinearity (VIF˃3), were observed between dietary C18:2 intake and intakes of C18:1, C18:3, and RUFAL. Therefore, intakes of C18:1, C18:3, and RUFAL were removed from the models.
Increasing dietary C18:2 intake from 143 to 760 g/day linearly decreased DM intake, 4% fat-corrected milk, milk fat concentration, and milk fat yield. Milk protein concentration and yield, however, were not affected by increasing dietary C18:2 intake. Results of this meta-analysis show that ingredients containing high concentrations of linoleic acid should be limited in lactating cow diets when the objective is to maximize milk production performance.
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