Results and Discussion
Rumen volatile fatty acids were unaffected by treatment (data not shown). Results for milk proximate analysis and yield are shown in Table 1. Milk protein and SNF increased as dietary inclusion of DDGS increased. As observed in other studies involving the feeding of DDGS to lactating dairy cows, significant milk fat depression was observed when cows were fed both the 10% and 25% diet as compared with the 0% DDGS diet.
Degree of milk fat depression did not differ significantly between the 10% and the 25% DDGS treatments. Mean daily milk yield was not different for the 0% and 10% DDGS treatments (P = 0.636), but decreased significantly when cows were fed the 25% DDGS diet (P = 0.046). Feed analysis (data not shown) confirmed that, as intended, diets were isoenergetic; however, feed intake was not measured in this experiment, which could account for some of the observed differences in daily milk production.
Milk fatty acid composition was altered (Figure 1) by treatment. The ratio of saturated to unsaturated fatty acids decreased as dietary inclusion of DDGS increased (0 % DDGS = 1.72:1, 10% DDGS = 1.41:1, 25% DDGS = 1.27:1). The decrease in the proportion of saturated to unsaturated fatty acids was accompanied by a concomitant increase in HPI as dietary DDGS increased (0% DDGS = 0.47, 10% DDGS = 0.65, 25% DDGS = 0.72), indicating that that the fatty acid composition of milk from cows fed DDGS may be more desirable from a health perspective.
As was hypothesized and has been previously reported, milk from cows fed DDGS contained higher concentrations of unsaturated fatty acids. The increased concentration of unsaturated fatty acids in the milk from the cows fed 10% and 25% DDGS, however, did not result in a decrease in oxidative stability or an increase in development of off-flavors in the milk. No meaningful differences in FFA, peroxides, or oxidative stability of milk from any treatment were detected.
Additionally, no significant differences in any off-flavor attributes, as evaluated by a trained sensory panel, occurred as a result of treatment or treatment by storage time (data not shown). These results indicate that the feeding of DDGS to lactating dairy cows did not result in milk that was less oxidatively stable and, consequently, more prone to development of off-flavors. In addition, milk from cows fed DDGS may be “healthier” as indicated by the HPI data.
Finally, it is worthy to note that the feeding of 25% DDGS by DM to lactating dairy cattle resulted in a significant decrease in milk production, indicating that a 25% DDGS diet by DM may not be advisable.
Source: Iowa State University- Eric Testroet, Graduate Research Assistant; Gerui Li, Former Graduate Research Assistant; Stephanie Clark, Associate Professor; Don Beitz, Distinguished Professor, Department of Animal Science