Quantification of the effects of energetic nutrients on fat content of cow milk

Abstract

A decreased fat content of milk seems to be a necessity for the future at least in European countries. This can be obtained by genetic or nutritional ways. This paper tries to quantify possibilities offered by nutrition. Fat is the milk solid that can be the most easily modified in a nutritional way. Propionic acid, glucose, trans₁₀ C18:1 and trans₁₀, cis₁₂ CLA are the nutrients identified to reduce milk fat content and acetic acid and butyric acid are those that increase milk fat content. Seven meta-analyses of literature data of trials giving these nutrients as perfusions or as protected forms were performed. As a result, the efficiency to reduce milk fat content is - 0.006, - 0.003, - 0.09, and - 1.8 g/kg per gram of added nutrient for propionic, glucose, trans₁₀C18:1, and trans₁₀, cis₁₂ CLA and - 0.007, - 0.002 g/kg per gram of subtracted nutrient for butyric and acetic acids respectively. The mechanisms involved in these responses are reviewed. In the decrease of milk fat content induced by a 30 % increase of concentrate, glucogenic precursors (propionic acid and glucose) explain 54 % of the drop of milk fat content, trans₁₀ containing fatty acids (trans₁₀C18:1 and trans₁₀, cis₁₂CLA) explain 34 %, and precursors of de novo fatty acid synthesis (acetic, and butyric acids) explain 21 %. In conclusion, a decrease of milk fat content with some diets is multi-factorial, and a pluri-nutrient approach is proposed in replacement of the usual mono-nutrient approach in order to understand the variations of milk fat content.