Feeding dried distillers grains with solubles affects composition but not oxidative stability of milk

Feeding lactating dairy cows dried distillers grains with solubles (DDGS) increases the concentration of unsaturated fatty acids in the milk from those cows, potentially leading to increased susceptibility to development of off-flavors. Feeding DDGS has been loosely implicated to be a cause of development of spontaneous oxidative off-flavor in milk. We hypothesized that increased feeding of DDGS would accelerate development of off-flavors and that fortification with vitamin E (0.06% wt/wt) or C (0.06% wt/wt) would prevent spontaneous oxidative off-flavors. The objective of this research was to determine the effects of feeding DDGS to lactating dairy cows on several parameters of milk quality as determined by both chemical and sensory evaluations. Twenty-four healthy mid-lactation Holstein dairy cows were fed total mixed rations containing DDGS (0, 10, or 25% dry matter). Cows were blocked by parity and randomly assigned to 1 of 2 groups (12 cows each). Each group received all 3 treatments in a 3-period Youden square design so that each cow served as her own control. Samples of milk from individual cows for proximate analysis and pooled milk for pasteurization and sensory analysis were collected on d 14, 21, and 28 of each experimental period. Pooled milk was assayed for peroxides and free fatty acids and evaluated by a trained sensory panel for the presence of 7 off-flavors common to milk on d 1, 3, and 7. Feeding 25% DDGS caused a significant decrease in daily milk yield. Increased dietary inclusion of DDGS also caused a concomitant decrease in percentage of milk fat and an increase in percentages of both solids nonfat and protein. Milk peroxides and free fatty acids were almost all below the detection limit, and the few exceptions were not found in replicated analyses. Sensory analysis revealed off-flavors only in milk from cows fed 0% DDGS when that milk was stored for 7d and when milk from cows fed 25% DDGS was fortified with 0.06% (wt/wt) vitamin C. Those few detected off-flavor scores were less than 1.5cm on a 15-cm line scale, indicating that the differences are not practically significant. Peroxide values support the findings by the sensory panel that both feeding DDGS at 10 and 25% and vitamin E and C fortification did not practically change the oxidative stability of milk. These results, taken together, indicate that feeding DDGS under our experimental conditions modified milk composition, but did not contribute to the development of off-flavors in milk.