FATTY-ACID DIGESTIBILITY IN LACTATING COWS FED INCREASING AMOUNTS OF PROTECTED VEGETABLE OIL, FISH OIL OR SATURATED FAT

Fatty acid digestion was studied in three dairy cows cannulated in the rumen, duodenum and ileum. Cows were fed encapsulated fat sources (vegetable oil, saturated fat and fish oil). A preperiod diet was fed with no added fat. In a graeco-latin design nine diets comprising three levels of each of the three fat sources were fed. The preperiod diet contained 230 g fatty acids (FA), whereas the three other fats were fed at about 550, 850 and 1150 g FA/day. The feed-ileum true digestibility of total FA was 95, 47 and 86% for vegetable, saturated and fish fat, respectively. The true digestibility of FA was for all fat sources independent of fat level. The FA digestibility of C16:0 was higher than that of C18:0. The experiment supports the theory that unsaturated FA has a synergistic effect on the digestibility of saturated FA. Bile acid secretion was estimated to be 282-550 g/day, with the lowest secretion for fish fat diets. Secretion was independent of the amount of fat fed.