Influence of type of diet on the fat constituents of goat and sheep milk

Abstract

The specific composition of milk fat of the small ruminant makes it especially valuable nutritionally and for consumer health. The aspects of the nature and composition of the animal's diet that have an influence on the fat content of its milk and its composition has been reviewed. The various studies have been, fundamentally, aimed at optimising the production of milk. Particular account is taken of the industrial use made today of sheep and goat milk, as it comprises the raw material for the manufacture of different dairy products, especially of cheese. The physical form in which the forage proportion of the diet is presented and/or the forage/concentrate ratio in the diet are aspects for special consideration in determining the fat content of the milk. In the case of the goat, this seems to depend particularly on the energy intake achieved in each case. Dietary supplementation with different types of fat, unprotected or protected against the ruminal metabolism, is considered a crucial strategy. Not only does this alleviate certain limitations in the diet provided from the production system that is practiced. The semi-extensive production system of the small ruminant is most common in arid and semi-arid zones. It enables the producer to control the content and composition of milk fat. The scope of effect depends on the nature and amount of the dietary fat and on the existence of interactions between the basal diet (forage type, starchy concentrate, etc.) and dietary lipids. Besides the production system, the involvement of other factors, such as stage of lactation and the productive capability of the animal, should, also be taken into account. From the available information, it can be concluded that the nature of fat content of sheep and goat milk, in comparison with cow milk, presents advantages for consumer health. This composition makes them directly or in the form of dairy products, foods of choice for segments of the human population with specific requirements. Different nutritional strategies are designed with the aim of optimising the composition of these milks with respect to their fat content and composition. Experimental results in goat nutrition, show that lipid supplementation does not change net energy intake and milk yield, but increases in most cases, milk fat content and allows much less saturated fatty acids, much more oleic and/or vaccenic and rumenic acids, more linolenic acid, and other trans fatty acids. The responses of goats are different from cow's responses in many aspects of milk production and mammary lipid metabolism, and the same is probably true for sheep. The variation in milk fat composition is very large, with important interactions between forage, concentrates and oils, in almost all major and minor fatty acids. Supplementation of corn silage or high-concentrate diets with vegetable oils increases sharply trans fatty acids other than rumenic and vaccenic acids. The aim of future research is to improve the effects of different feeding strategies, in order to increase more selectively fatty acids that are of interest for human nutrition and health without increasing the less desired fatty acids, and without decreasing the sensory quality of dairy products.