| Late blowing in Swiss cheese, a result of unwanted gas production during ripening, is unacceptable to consumers, and causes economic loss to manufacturers. Cheese processors have raised concerns that feeding dried distillers' grains with soluble (DDGS) to cows leads to this defect, in part, because of Clostridial spores. Apart from that, in order to minimize bacterial contamination, antibiotics are being used in industrial ethanol fermentations. Residual antibiotics in DDGS could lead to inadvertent feeding of antibiotics to animals is also of concern. In this study, the effect of feeding DDGS to lactating dairy cows on composition and quality of milk and baby Swiss cheese was examined. Thirty healthy multiparous and mid-lactation Holstein cows were assigned randomly to one of three dietary treatment groups (10 cows per treatment group): (1) total mixed ration (TMR) with no DDGS, (2) TMR with 10% DDGS by dietary DM, and (3) TMR with 20% DDGS by dietary DM in a 3 x 3 Latin square with repeated measures. One complete milking from all cows within a treatment was collected and pooled for cheese-making trials, twice within each month of the three-month study. Additionally, individual milk samples from three milkings of a day were collected weekly, and proximate analysis was carried out on pooled individual milk samples. The milk and DDGS were analyzed for Clostridial spores. Milk and DDGS samples were sent Iowa State University Veterinary Diagnostic Laboratory for drug screening. Within 48 hr incubation in modified reinforced clostridium lactate medium, tubes containing milk, cheese, TMR, and manure showed gas formation. Conversely, DDGS used in our study was not a source of gas-producing spores. Feeding 10% and 20% DDGS decreased milk fat content (P < 0.0001) and increased the solids nonfat (P < 0.005), protein (P < 0.05), and lactose concentration of milk (P < 0.05) when compared with the milk from cows fed the control diet. After 60 days ripening, baby Swiss cheese had typical propionic acid Swiss cheese aroma. Regardless of diet treatment, pinholes, slits, and cracks were seen throughout most cheeses. Feeding of DDGS increased the amount of long-chain unsaturated fatty acids and decreased short-chain and most medium-chain fatty acids in the baby Swiss cheese. All the analytes tested, including virginiamycin, a commonly used antibiotic during ethanol fermentation process, were below the detection limits Additionally, the antimicrobial effect of DDGS on the growth of Salmonella Typhimurium, Listeria innocua, E. coli ATCC 25922, Staphylococcus aureus, Pediococcus acidilacti, Lactobacillus casei, Lactobacillus acidophilus, Bacillus licheniformis, Paenebacillus odorifier, Pseudomonas fluorescens, and Paenebacillus amyloliticus were investigated using the disk diffusion seeded agar overlay method. Neither the buffered nor non-buffered DDGS solutions yielded any zone around the disk against any microorganism tested, indicating that the DDGS soluble fraction had no antimicrobial properties against any of the organisms tested. These results indicate that the DDGS analyzed in this study can be used as livestock feed without fear of inadvertent feeding of antibiotics. Although feeding cows with DDGS, modified milk composition and subsequently the cheese composition, DDGS could not be blamed as a source for gas-producing spores or for quality defects in Swiss cheese, but, rather, the gas-producing spores likely originate from the cow herself or the environment. |
