Effects of microwaving, and moist and dry heating on ruminal degradability of protein and dry matter in soybean meal

Two experiments were conducted to evaluate the effects of microwaving, autoclaving (moist heating), and roasting (dry heating) on gas production parameters and in situ rumen degradability of soybean meal (SBM). SBM was treated by roasting at 140℃ for 30 and 60 min, and at 160℃ for 30 and 60 min, autoclaving at 121℃ for 20 min, and microwaving for 2, 4, and 6 min. A gas production trial was performed using rumen fluid collected from fistulated sheep. Cumulative gas production was recorded at 2, 4, 6, 8, 12, 24, 36, 48, 72, and 96 h after incubation. The organic matter digestibility (OMD), metabolizable energy (ME), net energy (NE), and short-chain fatty acid (SCFA) in gas production trial were calculated after 24 h incubation. For in situ technique, three fistulated sheep of the Dalaq breed (with an average weight of 54 ± 1 kg) were housed in individual cages and fed at the level of maintenance. Samples of the processed and unprocessed SBM were ground to pass through a 3 mm screen, and 5 g of each sample were transferred into nylon bags. The results showed that treatments had a significant effect on gas production potential (P<0.05). With increasing the heating duration, gas production potential increased in roasted treatments. Processing methods significantly reduced gas production (P<0.05). The lowest volume of gas production was recorded for the autoclave treatment. Processing with Micro-6 and moist heating (autoclave) resulted in a significant decrease in organic matter digestibility (OMD) compared to dry heating (roasting). Micro-6 treatment significantly (P<0.05) decreased the concentration of SCFA compared to other treatments. The results of in situ experiments showed that processing of SBM significantly reduced the rate of dry matter and protein degradation (P<0.05). Processed SBM had a lower rapid degradable fraction (a) and higher slowly degradable fraction (b) compared to the control treatment. In conclusion, the methods of heating (autoclaving, dry heating, and microwaving) of SBM decreased the gas production and gas production rate and ruminal protein degradability.