84 Evaluating the effects of hind gut acidosis in sheep on rumen fermentation ex vivo

The objective was to determine the effect of hindgut acidosis in sheep on rumen fermentation ex vivo. Eleven ruminally and cecally cannulated ewes [body weight (BW) = 49 ± 4 kg] were assigned to one of two treatments: a constant infusion of deionized water (CON; 26 mL/kg BW per 24 h) or starch solution (STA; 3 g wheat starch/kg BW per 24 h) in the cecum to induce hindgut acidosis. Rumen fluid was collected from each ewe on the d before and four d after the start of cecal infusion for an ex vivo fermentation. There were four flasks for each ewe with two flasks per substrate. The two substrates were forage-based (FB; 40% grass hay pellet, 35% whole shell corn, 15% dried distiller’s grain, and 10% alfalfa cubes) and concentrate-based (CB; 75% whole shell corn, 15% dried distiller’s grain, and 10% alfalfa cubes). Flasks contained 2.5 grams of substrate and 150 mL of inoculum (2:1 ratio of McDougall’s buffer and rumen fluid). Four sealed ANKOM F57 bags were filled with 0.25g DM of substrate and placed into flasks to determine in vitro dry matter disappearance (IVDMD). The flasks were incubated at 39°C for 24 h, with sample aliquots collected at h 0, 8, and 24 to determine pH, volatile fatty acids (VFA), and ammonia. Data were analyzed using the MIXED procedure of SAS 9.4. For all response variables, values from the run before cecal infusion initiation were included in the model as a covariate. Ammonia, pH, and VFA were analyzed with the effects of treatment, time, and their interaction. For the CB substrate, there was no effect (P = 0.90) of cecal infusion on ammonia concentration; however, there was a time effect (P = 0.01) with h 24 having a greater ammonia concentration than h 8. For the FB substrate, there was a tendency for STA to have lesser (P = 0.10) ammonia than CON. There was no effect (P ≥ 0.78) of cecal infusion treatment on pH for both substrates; however, there was a time effect (P = 0.01) with pH decreasing over time. In both substrates, there were no effects (P ≥ 0.23) of cecal infusion treatment on IVDMD, VFA concentration, acetate, or propionate molar concentration. However, butyrate molar concentration tended to be less (P = 0.07) for STA ewes for the CB substrate. No treatment differences were observed in butyrate for the FB substrate (P = 0.35). Results indicate that induced hindgut acidosis in sheep did not affect rumen fermentation ex vivo.