Effect of roasted soybeans and corn on performance and ruminal and blood metabolites of dairy calves.

Newborn Holstein calves (n = 132) were used to evaluate three protein sources (soybean meal and soybeans roasted to an exit temperature of 138 or 146 degrees C) that contained 30, 45, or 52% RUP, respectively. Each was used with either raw corn or corn roasted to an exit temperature of 135 degrees C. Roasting of corn increased starch gelatinization from 34.8 to 118.6 mg of maltose equivalents/g of sample. Six pelleted isonitrogenous calf starters (18% CP) were fed for ad libitum consumption from 0.5 to 8 wk of age. Performance of calves fed soybeans roasted at 146 degrees C plus raw corn was superior to that of calves fed soybean meal plus raw corn but was similar to the performance of calves fed soybean meal plus roasted corn. Roasted corn tended to improve calf performance when used with soybean meal and, to a lesser degree, when used with soybeans roasted at 138 degrees C but depressed performance when used with soybeans roasted at 146 degrees C. Ruminal concentrations of NH3, butyrate, and total VFA and plasma concentrations of urea were higher for calves fed soybean meal. Ruminal pH and lactate, plasma NEFA, and blood BHBA concentrations were unaffected by starter. Performance was superior when calves consumed protein and corn sources with similar degrees of ruminal availability.