Recent research on the origin of milk fat

Abstract

The two main problems of milk-fat secretion are its origin and its difference in composition from body fats. Whereas ox depot fatty acids consist chiefly of stearic, palmitic and oleic acids, cow’s milk fat contains about 10% of the C 4 to C 12 acids (see Hilditch 1956). The problems of origin and composition are, of course, related, and an answer to one is likely to go far in providing an answer to the other. The subject has been extensively reviewed (Folley 1949, 1956; Popják 1951-52, 1952; Shaw & Lakshmanan 1957) and it is intended here to deal only briefly with material that has been discussed in greater detail by others. Further, this review is confined almost entirely to research on the glyceride fat of ruminant milk. Other lipids are present in negligible proportions (Jack & Smith 1956) and space permits reference to other species only for purposes of comparison.

Milk composition in relation to rumen metabolism

“…It is this change in the production of acetic and propionic acids that has generally been held to be responsible for the depression in synthesis of milk fat, a point of view that has received considerable support from the knowledge acquired in the past 10-15 years (see Folley, 1956; Glascock, 1958). Milk fat arises from two main sources: part (estimated at 20-30%) is derived from a fraction of the 'neutral fat' of blood plasma which has its origin in dietary fat; the remainder is synthesized within the mammary gland from glycerol, which is itself synthesized from hexose units either in the liver or mammary gland, and from fatty acids of chain length VOl.…”