The effects of induced hindgut acidosis in sheep on rumen fermentation and gut permeability.

The objective was to determine the effects of induced hindgut acidosis in sheep on cecal pH, ruminal fermentation, and gut permeability. Eleven ruminally and cecally cannulated ewes (49 ± 4 kg) were assigned to one of two treatments: control (CON; n = 5) or induced hindgut acidosis (HGA; n = 6). To induce hindgut acidosis, 3 g wheat starch/kg BW per 24 h was continuously infused via the cecal cannula for 4 d. Control ewes received a constant infusion of deionized water. Ewes were fed a common diet at a set level of intake based on body weight. Chromium EDTA was dosed once daily via the cecal cannula as a marker of gut permeability. Rumen, cecal, and fecal samples were collected to determine pH and volatile fatty acids (VFA). Rumen fluid was collected on day 4 for an ex vivo fermentation to determine pH, VFA, ammonia, and in vitro dry matter digestibility (IVDMD). On day 5, sucralose was infused through the cecal cannula and blood was collected from a mesenteric catheter under anesthesia. Transepithelial electrical resistance (TEER) was determined in the ileum, cecum, and colon in Ussing chambers. There was a treatment × time effect (P = 0.05) for cecal pH, with HGA ewes having lesser cecal pH after day 1. By day 4, cecal pH had dropped to 5.07 for HGA ewes compared to 6.40 for CON ewes. A treatment × time interaction was observed (P < 0.01) for fecal pH and followed the same trend as cecal pH. Total fecal VFA concentration was greater (P < 0.01) in HGA ewes than CON. Rumen pH was not affected (P = 0.87) by the interaction of treatment × time, but was affected (P < 0.01) by treatment, as ewes on the HGA treatment had a lesser rumen pH than CON ewes. Control ewes had lesser ruminal VFA and ammonia concentrations than HGA ewes (P < 0.01). Despite this, the ex vivo fermentation did not indicate any differences in pH, VFA, or IVDMD (P ≥ 0.11). Urinary Cr recovery was not affected by the interaction of treatment × time, or treatment (P ≥ 0.13). There were no effects (P ≥ 0.22) of treatment, time, or their interaction on mesenteric plasma sucralose concentration. In cecal tissue, TEER tended (P = 0.09) to be lesser, indicating increased permeability in HGA ewes compared with CON ewes. In contrast, TEER was not different (P ≥ 0.83) in ileal or colonic tissues between treatment groups. A cecal infusion of starch induced hindgut acidosis and affected hindgut fermentation. Hindgut acidosis still had systemic effects on rumen conditions despite varied responses in gut permeability.