ASAS / ADSA Ruminant Nutrition : Feed Additives , Rumen Fermentation , Minerals , and Transition Cows

Gas production (GP) and starch degradation (STAD) from starchy feedstuffs were measured simultaneously by in-vitro incubation in buffered rumen fluid after 0, 4, 6, 8, 12, 16 and 24 h incubation to explore the possibility to estimate STAD via GP technique for starchy feedstuffs. The results showed the ranking in the initial degree of starch degradation and gas production. Potato starch and maize had the slowest initial rate, and tapioca, corncob mix and barley had the fastest ones in STAD. Starch degradation of Over 75% took place after 6-h incubation and nearly finished completely in 24-h incubation. Potato starch and maize, likewise, had the slowest initial rate of gas production, and however the fastest initial rate was found in the samples with smallest total starch content (TSC) such as pea and barley. Gas production was in line with the starch degradation, but the linking degree between GP and STAD varied with the samples with different TSC, especially in the initial incubation. Overall regression indicated a strong correlationship between GP and STAD with R2 0.88 and for individual sample, R2 ranged from 0.93 1.00. The regression relationship was affected by TSC of the sample. A larger TSC displayed a higher coefficient and constant as well. R2 for the constant and coefficient regression with TSC was 0.88 and 0.91 respectively. The multiple linear regression was made via TSC and GP as two main predictors: STAD=-318.14+0.427*TSC+1.876*GP(R2=0.95, RSD=48.71, P=0.0000). The estimation equation was further modified by using GP as main predictor and its constant and coefficient was, however, indirectly estimated by incorporating the regressions of constant and coefficient with TSC instead of direct estimation: STAD=(0.2088*TSC+168.55)+GP*(0.00136*TSC+0.9654)(R2=0.97, RSD=41.2, P=0.0000). R2 and RSD in both equations were well improved if compared with the values of 0.88 and 76.15 of the regression using GP as unique predictor. The much higher in R2 and RSD of the second equation indicated the modified equation was more accurate and robust. Gas production technique can be used to estimate the rate and extent of starch degradation in rumen fluid, as long as the starch content is taking into account.