Use of a corn milling product in diets for dairy cows to alleviate milk fat depression

Various diet formulation strategies were evaluated to alleviate milk fat depression using a corn milling product (CMP) that contained approximately 28% crude protein, 34% neutral detergent fiber (NDF), and 12% starch (dry basis). The control diet comprised mostly corn silage, alfalfa silage, corn grain, and soybean meal and contained approximately 22% forage NDF (fNDF), 28% total NDF, and 33% starch. Another diet included 25% CMP that replaced corn grain and soybean meal and contained 27% starch and 33% NDF. Two other diets included 25 or 40% CMP that replaced forage and concentrate and contained 19 and 17% fNDF, 31 and 32% total NDF, and 30 and 28% starch, respectively. Diets were fed to 16 mid-lactation Holstein cows in 4 replicated 4 × 4 Latin squares. Milk fat percentage was low for the control diet (2.9%) but increased to 3.5% when cows were fed the diet with 25% CMP that replaced concentrate. Cows fed diets with 25 or 40% CMP that replaced forage and concentrate also had low milk fat percentages (3.0 and 2.9%, respectively). Intake was lowest for cows fed the control diet. Milk yield was reduced when CMP replaced only concentrate but because of the substantial increase in milk fat, the yield of energy-corrected milk was greater. Calculated energy use (maintenance+milk+body weight change) divided by dry matter intake was similar for the control and for the diet in which CMP replaced only concentrate, but it decreased linearly as increasing amounts of CMP replaced both forage and concentrate. A quadratic equation using the ratio of dietary starch to fNDF was the best predictor of milk fat percentage (ratios >1.4 were associated with reduced milk fat). Overall, CMP was effective at alleviating milk fat depression when it replaced corn grain but not when it replaced forage and concentrate.