A meta-analysis to determine the optimal values of precursors in the diet of dairy cows that increase the concentration of conjugated linoleic acid (CLA) in milk

. The concentration of conjugated linoleic acid (CLA) in dairy products derived from ruminants, such as cow’s milk, is mainly influenced by the dietary lipid profile. The current study aimed to establish the relationship between fatty acid (FA) profiles in various diets and the concentration of CLA in bovine milk using a meta-analysis. A total of 63 articles were selected, comprising 35 studies involving oilseeds, 13 – fish oil, and 15 – grass as the sole food source. A general linear model was constructed for each ingredient and CLA concentration was optimised with respect to the FA that showed the greatest effect (C18:0, C18:2 and C18:3) in the model. The relationship between FA concentrations in the diets, presentation method (seeds and pasture), type (seeds), and basal diet (fish oil), and the CLA content in milk was assessed using analysis of covariance, followed by Tukey’s test ( P = 0.05). It has been demonstrated that an increase in the total concentration of C18:0, C18:2, and C18:3 in the diets does not necessarily guarantee a higher CLA level in milk. This phenomenon is attributed to ruminal FA metabolism and metabolic processes within the animal itself. Consequently, it can be concluded that a quadratic relationship exists between the concentration of dietary FAs and the concentration of CLA in milk.