To evaluate the effect of heat treatments on the effective degradability of soyabean crude protein in the rumen, we conducted the nylon bag incubations and rumen passage rate estimates for raw and heated soyabean. Three types of heated soyabeans were prepared by roasting rolled raw soyabean at 400℃ for 30, 60 and 120sec. The rumen degradation characteristics and passage rate constant for each soyabean were determined via the nylon bag technique and the marker pulse dose procedure. The nylon bag incubations and ruminal passage rate estimates of the soyabeans were conducted using three rumen fistulated weathers and four Holstein lactating cows, respectively. The results obtained were as follows, 1) The soluble portion (%), degradable portion (%) and degradation rate constant (/h) of crude protein for raw soyabean, heated for 30, 60 and 120sec were 55, 45, 0.06; 19, 81, 0.04; 11, 89, 0.05 and 10, 83, 0.06, respectively. 2) The ruminal passage rate constant (%/h) for raw soyabean heated for 30 60 and 120sec were 1.94, 3.04, 2.26 and 3.18, respectively. 3) The effective ruminal degradability of crude protein (%) for raw soyabean, heated for 30, 60 and 120 sec were 86.4, 63.2, 69.5 and 61.6, respectively, and was significantly higher (P<0.05) for raw compared to heated soyabeans. There was no statistically significant differences in the effective ruminal degradability among the heated so yabeans.
Key words: Rumen degradability; soyabeans; heat treatments; nylon bag technique.