Materials and Methods
Twenty commercial dairy herds near Wooster, OH were chosen to participate in this study because milk from those herds represented a wide range in milk fatty acid composition, milk flavor score, and concentrations of whole soybeans in the diet. Bulk tank milk from those herds was sampled at approximately one month intervals between December, 1998 and April, 1999. Diets were also sampled during that time period. Milk was analyzed for fat, protein, urea nitrogen, and somatic cell count by DHI Cooperative (Powell, OH) and for milk fatty acid profile and concentrations of copper, manganese, zinc, vitamin E, β-carotene, and vitamin C. Milk samples were also evaluated for flavor by a trained panel. The flavor scoring system was: 0 -1= normal; 1-2 = slight oxidized flavor; 2-3 = moderate oxidized flavor; 3-5 = strong oxidized flavor; and >5 = intense oxidized flavor. Milk was evaluated on the day of collection (day 0) and on 3 and 8 days after collection. During the storage period, milk was stored refrigerated. Diets were analyzed for nutrients using standard procedures. Correlation and regression analysis was used to quantify relationships between milk composition and concentrations of whole soybeans in the diet and between milk composition, dietary soybeans, and milk flavor.