Observations on Rumen Fluid, Blood Serum, and Milk Lipids of Cows Fed Methionine Hydroxy Analog

Twelve dairy cows were assigned to each of three groups which received either 0, 40, or 80 g of methionine hydroxy analog per day in their grain. Milk and fat yields were increased by supplementation. Milk fat of supplemented cows compared to that of the controls contained more of the 18-carbon fatty acids and less of the short-chain fatty acids. Cows receiving methionine hydroxy analog had more blood serum lipids (P < .01); but, there were only minor differences in the composition of these lipids between the three groups. Feeding of methionine hydroxy analog decreased the free fatty acids in rumen fluid and apparently promoted the formation of an unidentified polar lipid. The relative proportion of stearic acid was lower in the rumen fluid of those cows fed methionine hydroxy analog (P < .05).