Acetate Production in the Rumen of Cows Fed Either Control or Low-Fiber, High-Grain Diets

Measurements were made on acetate production in the rumens of cows fed a diet supporting a normal fat content of the milk and in the rumens of cows fed a milk-fat depressing diet (low-fiber, high-grain). An isotope dilution technique, using acetate-1- 14 C, coupled with the use of polyethylene glycol (M.W. 4000) as a rumen volume marker was employed. Mean acetate production values of 29.3 and 28.1 moles per 24 hr were obtained for the control and high-grain diets, respectively. It was concluded that an absolute shortage of acetate, because of reduction in amount of acetate produced in the rumen, is not responsible for the depression in the fat content of the milk when a low-fiber, high-grain diet is fed.