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 1 38 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 temperat ure of 135 degrees C. Roasting of corn increased starch gelatinization from 34.8 to 118.6 mg of maltose equivalents/g of sample. Six pellete d isonitrogenous calf starters (18% CP) were fed for ad libitum consum ption from 0.5 to 8 wk of age. Performance of calves fed soybeans roas ted 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 calve s fed soybean meal plus roasted corn. Roasted corn tended to improve c alf performance when used with soybean meal and, to a lesser degree, w hen used with soybeans roasted at 138 degrees C but depressed performa nce when used with soybeans roasted at 146 degrees C. Ruminal concentr ations of NH3, butyrate, and total VFA and plasma concentrations of ur ea were higher for calves fed soybean meal. Ruminal pH and lactate, pl asma NEFA, and blood BHBA concentrations were unaffected by starter. P erformance was superior when calves consumed protein and corn sources with similar degrees of ruminal availability.