Fat supplementation of dairy rations and its consequences on milk quality in dairy cows

Abstract

Fat supplementation of dairy rations is often practised. This decreases milk protein content, especially the casein fraction. The causes are up till now not well known. A part of this effect is related to the dilution of the proteins in a higher milk volume since total protein secretion is not greatly altered. The decrease in protein content is very slight in early lactation where the positive effect on milk yield is less marked than in mid-lactation. Fat supplementation has a variable effect on butterfat. This effect depends on the balance between the increase in dietary long-chain fatty acid uptake by the udder and the decrease in mammary synthesis of short-and medium-chain fatty acids. The content of milk in polyunsaturated fatty acids is in most cases not increased, due to ruminal hydrogenation of dietary fatty acids. Encapsulation of lipids by protected proteins is the only technique which prevents ruminal hydrogenation of polyunsaturated fatty acids. Some kinds of lipid supplementation lead to a lowering of the organoleptic value of dairy products, especially through oxidation and rancidity.