Risk of milk fat depression for dairy cows fed high moisture corn and distillers grains in diets containing monensi

Competition for corn for fuel ethanol production and resulting increases in prices for corn, is driving dairy producers towards using alternative ingredients to increase production efficiencies. Feeding distillers grains from corn ethanol production provides a low-cost, nutrient dense alternative to corn, but concerns exist that when distillers grains are fed milk fat may be depressed. Likewise feeding an ionophore, monensin, will increase efficiency of milk production. Feeding monensin has also been associated with decreased milk fat production. Lastly, feeding large quantities of highly fermentable starch has been associated with milk fat depression. To better understand the interaction of these factors, an experiment was conducted feeding distillers grains and a highly fermentable starch source (high moisture corn) to lactating dairy cows having monensin in their diets. In a 2 x 2 factorial design, dairy cows were fed normal or low-fat distillers grains and dry or high moisture corn. All diets contained monensin and the experiment lasted for 6 weeks. Cows fed normal distillers grains demonstrated lesser concentrations of acetate and an increased proportion of acetate to propionate in rumens. Yields of milk were not changed by feeding distillers grains, but percentage of fat in milk was decreased with distillers grains. Cows fed high moisture corn also had lesser concentrations of acetate in rumen fluid, but the acetate to propionate ratio was not effected by the type of corn fed. Feeding wet corn decreased milk yield as well as the percentage and yield of milk fat; however, concentrations of protein in milk were increased by feeding high moisture corn. The greatest negative effects on milk fat concentrations and yields were obtained when high moisture corn was fed in combination with distillers grains. Feeding high-protein distillers grains increased the production of fat-corrected milk, while feeding high moisture corn decreased production and efficiency of production of fat-corrected milk. Results indicate that both distillers grains and high moisture corn may decrease milk fat production and that this effect is amplified when the two are fed in combination in diets containing monensin.