Optimum Proportion of Sweet Corn By-Product Silage (SCW) and Rice Straw in Total Mixed Ration Using in Vitro Gas Production

An in vitro gas technique was used to study the effects of different proportions of sweet corn by-product silage (SCW) and rice straw (RS) on in vitro fermentation. The dietary treatments were ratios of SCW and RS all on a on a dry matter (DM) basis: T1 = SCW: RS at 60:40; T2 = SCW: RS at 50:50; and T3 = SCW:RS at 40:60. The ration of concentrate and roughage was 60:40 on a DM basis. The DM, crude protein (CP), ether extract (EE), acid detergent fiber (ADF) and neutral detergent fiber (NDF) of SCW were 22.56, 7.11, 1.89, 41.34 and 78.45%, respectively. The results showed that cumulative gas production at 48 h and 72 h after incubation with the ratio of SCW to RS at 60:40 on a DM basis was significantly (p < 0.05) higher than the results from the ratio of SCW to RS at either 50:50 or 40:60 on a DM basis. The proportion of SCW and RS among treatments had no effect on true digestibility parameters. However, the in vitro organic matter digestibility parameters in the treatment group with SCW:RS at 60:40 on a DM basis were higher (p < 0.05) than in the other two treatments. The total volatile fatty acid in the treatment group with SCW:RS at 50:50 and 40:60 on a DM basis were higher (p < 0.05) than in the treatment group with SCW:RS at 60:40 on a DM basis. Acetic acid (C2), propionic acid (C3) butyric acid (C4) and the proportion of C2:C3 were not different (p < 0.05) among treatments. The levels of NH3N in all groups were not significant (p < 0.05) among treatments. It was concluded that the optimum level of SCW:RS was 60:40 on a DM basis.