In vitro ruminal fermentation kinetic of diets containing forage cactus with urea and different starch sources

The study was conducted to evaluate fermentation kinetic of diets based on cactus forage enriched with urea and Tifton 85 hay, containing different starch sources, using semi-automated in vitro gas production technique. Treatments were disposed in a randomized block design, with four replications where concentrates were formulated as follows: cassava roots (FSMa), semi flint corn grains (FSMiSD), dent corn grains (FSMiD) and wheat bran (FTMa). All diets were formulated to obtain 15% of crude protein. Gas pressure were measured 2, 4, 6, 8, 10, 12, 15, 18, 21, 24, 30, 36, 48, 72 and 96 h after inoculation. For fast phase maximum gas volume (Vf1), both treatments containing corn did not differ (P>0.05). FTMa differed (P<0.05) from diets composed with corn, as main starch source. Specific degradation rate of fast fraction (Kd1) was higher (P<0.05) on FSMa and FTMa diets, compared with corn diets. Colonization time (L) showed lower values (P<0.05) for FTMa diet. The lowest total gas production was observed on FTMa and the highest for FSMiD, varying from 225.49 to 268.31 mL/g, respectively. Cassava roots as starch source contributes to a faster fermentation, compared to both corns, allowing a better synchronization with faster degradation nitrogen sources.