Impacts of dietary fat level and saturation when feeding distillers grains to high producing dairy cows.

This experiment was conducted to determine whether increasing the net energy (NEL ) of a total mixed ration (TMR) with mainly unsaturated fat from corn distillers dried grains with solubles (DDGS) vs. rumen inert (RI)-saturated fat has similar impacts on animal performance. The experiment was an incomplete Youden square with three treatments and four 28-days periods, completed on a large commercial dairy using three early lactation pens each with approximately 380 multiparity cows. The TMR for all treatments was the same, except for 150 g/kg dry matter (DM) of each TMR which contained 90 g/kg high-protein DDGS (HPDDGS) and 60 g/kg beet pulp (i.e. low-fat control diet; LFC); 150 g/kg DDGS (i.e. high-fat diet with unsaturated fat; HFU); or 111 g/kg HPDDGS, 20 g/kg beet pulp and 19 g/kg RI fat (i.e. high-fat diet with saturated fat; HFS). The DM intake was highest (p < 0.05) for HFU-fed cows. Milk, fat and true protein yields, as well as milk energy output, were higher (p < 0.01) when cows were fed HFS vs. HFU and LFC diets. Milk true protein concentration was lowest (p < 0.01) for HFS-fed cows, but milk fat % was lowest (p < 0.01) for HFU and highest (p < 0.01) for HFS-fed cows. There were numerous differences (p < 0.01) in milk fatty acid levels amongst diets. The increase in body condition score was lowest (p < 0.01) for LFC. Whole tract digestibility of acid detergent fibre was lower (p < 0.01) for LFC vs. HFS cows, and fat digestion was lowest (p < 0.01) for LFC-fed cows. This DDGS, high in unsaturated fatty acids, was fed at high levels (i.e. 152 g/kg DM) with little impact on animal performance vs. a lower fat control diet, although addition of an RI-saturated fat to create a diet with a similarly higher fat level resulted in higher animal productivity. Journal of Animal Physiology and Animal Nutrition