Influence de la mise à l'herbe des vaches laitières sur les indices de la matière grasse du beurre et sur les teneurs en différents acides gras poly-insaturés

Abstract - Influence of turning dairy-cows out to grass on the indices and the quantity of the various polyunsatured fatty acids in the butter fat
The faut of butter made from the morning and evening milk of different groups of cows in the herd at the C.N.R.Z. was studied over a period of a fortnight during which the cows were turn out to grass, in the spring of 1957, 1958 and 1959.
Variations in the iodine value and saponification values and the soluble and insoluble volatile fatty acids of the butter fat were recorded in 1957, whereas in 1958 and 1959 only the variations in iodine value were studied with additional determination of the various poly-unsaturated (conjugated and non-conjugated) fatty acids in the butter fat.
The increase in iodine value which occurs when fresh grass is introduced into the cow's diet may be abrupt (12 units in 48 hours) or less rapid depending on whether the change from the winter ration to pasture is sudden or gradual.
There is a correlated increase in the amount of conjugated diene acids (expressed as percentage by weight of butter fat), with the increase in iodine value (from 0,5 to 1,3 in 1958 and 0,5 to 1,8 in 1959 for a corresponding increase of 14 units in the iodine value). A simultaneous increase in linolenic acid (0,3 to 0,8) is observed, There is a transitory increase in the amount of linoleic acid which returns to its initial value several days after the cows are turn out to grass (1,5 in 1958 and only 1,0 in 1959). There is no variation in the amount of arachidonic acid (0,3 to 0,4)