In vitro fermentation parameters of brachiaria straw and starchy by-products

Our objective was to characterize the degradation kinetics of fibrous and starchy agro-industrial wastes that can be used as feed for ruminants. Unprocessed Brachiaria straw hay (UBH), processed (briquetting) Brachiaria straw hay (PBH), a starchy by-product from potato processing (SBP), and cassava starch (CST) were evaluated. Two diets were formulated: one including UBH and CST (UBH-CST); and the other PBH and SBP (PBH-SBP). For the study of degradation kinetics, the in vitro cumulative gas production fermentation technique was used, in which the two-compartment Monomolecular-G3G1 model provided a more likely fit. The cumulative gas volumes produced were 23.2 (UBH), 29.6 (PBH), 39.1 (SBP), 36.6 (CST), 27.9 (UBH-CST), and 28.5 (PBH-SBP) mL per 0.1 g of dry matter. The starchy feedstuffs showed more intense fermentation in the first hours ((K) over cap (1)=1.050 and 0.627, for CST and SBP, respectively). This agile fermentation occurs because this is a soluble and/or rapidly degradable feedstuff that contains a very small amount of fibrous matter. As for the fibrous feedstuffs, UBH and PBH, fermentation occurred more slowly in the first hours ((K) over cap (1)=0.212 and 0.121, for UBH and PBH, respectively), releasing less gas. Because fiber has a slowly degradable and insoluble part, the asymptotic phase takes longer to be reached. The diets, on the other hand, exhibited fermentation intermediate to those of the starchy and fibrous feedstuffs ((K) over cap (1)=0.141 and 0.127, for UBH-CST and PBH-SBP, respectively), what faithfully followed the gas production profile of their ingredients. Both diets showed lower k1 values and higher k2 values when compared to corn silage. The characterization of agro-industrial residues, using the in vitro cumulative gas production technique, confirms the real possibility of using the studied by-products in feeding ruminants.