The aim of this study was to investigate the effects of chemical processing of soybean meal on the amount of available crude protein at the duodenum (uCP) using a new modified gas technique. Evaluated samples were two samples of unprocessed soybean meal and one sample of processed soybean meal (heat processing with xylose) containing 495, 480 and 446 g/kg crude protein (CP), respectively. To perform the gas test, rumen fluid was collected before the morning feeding from two rumen fistulated Holstein dairy cows (640 ± 38 kg, body weight). Feed samples (200 mg) and blanks (only 30 ml of buffered rumen flouid) incubated simultaneously in three repeats and three runs for 8 and 24 hours. At the end of the each incubation time, the uCP was calculated as non-ammonia N which was calculated by subtracting the amount of ammonia N released in the incubation medium of the total incubated N (sum of N content of feed sample and ammonia N in blanks). Effective uCP (EuCP) was calculated via an exponential equation using the estimated uCPs at 8 and 24 h post incubation. Ratio of effective uCP (at the passage rate of 0.1/h) to the CP content of feed samples for processed soybean meal and two untreated soybean meals were 0.873, 0.747 and 0.785 (SEM=0.0355), respectively. These results showed that the processing had no significant effect on the amount of EuCP of soybean meal (P> 0.05). However, the amount of relative EuCP for processed soybean meal was 10-15 percent greater than untreated soybean meals.

Keywords