Fatty Acid Composition of Milk. I. Effect of Roughage and Dietary Fat

Abstract

Twenty-four Holstein cows were randomly assigned to treatment sequence and fed 2 levels of alfalfa hay (1.0 lb./100 lb. body wt. and 2.5 lb./100 lb. body wt.) and 3 types of concentrate (control, 6% added tallow, and 6% added cotton seed oil). Low-roughage intake lowered the per cent fat and lactose in the milk and increased total production, but did not affect production of 4% FCM. Feeding cotton seed oil depressed per cent fat, total fat, and 4% FCM on the low-roughage diet, but had no effect on the high-roughage diet where it was fed in lower amounts with lower concentrate intake. Tallow caused a small but significant increase in fat on the high-roughage diet. Cotton seed oil depressed the acids of milk fat from Cg through C14, with an increase in the C18 acids, but there was no change in the C16 acids. The effect of tallow was less than that of cotton seed oil, with most of the values being between those of cotton seed oil and the controls. Cotton seed oil and tallow showed their effects regardless of roughage level. Volatile fatty acids in the rumen were affected by the amount of roughage and dietary fat. Low roughage depressed the molar per cent acetate with an increase in propionic, butyric, and higher acids. Dietary fat increased valerate and higher acids due to the presence of these acids and their precursors in the dietary fat.