Factors Influencing Milk Fat Depression on Rations High in Concentrates

Abstract

Abstract Three continuous feeding trials involving a total of 36 cows were used to study milk fat depression on high-concentrate diets composed primarily of pelleted corn. Physiological changes that consistently accompanied a depression in milk fat percentage included: 1) a reduction in rumen acetic acid; 2) increases in rumen propionic and valeric acids; 3) a decrease in blood lipids; 4) a decrease in blood ketone bodies; 5) an increase in blood glucose levels; 6) increased body weight gains; 7) reduced milk production; 8) decreases in the short-chain as well as the palmitic and stearic acid components of the milk fat; 9) increases in the unsaturated fatty acid components of the milk fat. The following alterations in the pelleted corn ration resulted in some degree of improvement in milk fat percentage: 1) substitution of pelleted oats or herd mix; 2) feeding thyroprotein; 3) adding 3% urea; 4) administration of butyric acid. Unsuccessful alterations included: 1) addition of 25% soybean oil meal; 2) feeding five times daily; 3) addition of 5% lard; 4) administration of sodium acetate. The results support the concept that the major factors depressing milk fat test on high-concentrate diets involve a high level of glucogenic metabolites that reduce blood ketone and lipid levels and tend to stimulate a fattening type of metabolism at the expense of milk fat synthesis.