An in vitro investigation into the effects of postbiotic supplementation on stabilising equine hindgut pH

Dysbiosis of the intestinal microbiome is a precursor to hindgut acidosis. As microbial diversity and fermentation are influenced by diet, including a postbiotic could help maintain healthy gastrointestinal microbes and reduce acidosis risk.

It was hypothesised that including a postbiotic in batch culture would reduce the degree of pH decline and lactate accumulation during fermentation.

In vitro batch cultures with faecal inoculant were prepared with either low starch (LS) or high glucose (G) substrate to represent normal and acidic fermentation. Saccharomyces cerevisiae derived postbiotic was added at 280 μg (T1), corresponding to the recommended daily feeding rate for a 500 kg horse adjusted to the dry matter of the incubated substrate, and 560 μg (T2), representing twice this rate, and incubated for 48 h to assess effects on pH, gas, volatile fatty acids (VFAs), ammonia (NH₃), and d-lactate production.

Substrate G showed a faster decline in pH (P < 0.001) than LS at 6 and 12 h post incubation. Postbiotic concentration had a positive linear relationship with pH in G and observed higher (P < 0.001) pH for T1 at 6 h, and T2 at 6 and 12 h. Production of propionic, and acetic acids was increased (P < 0.001) with postbiotic at 12 h and 36 h, and butyric acid at 36 h (P = 0.05). d-lactate production was greater in G than LS (P < 0.001) at 12 h and lower at 36 h (P < 0.001). Postbiotics reduced lactate at 12 and 36 h (P < 0.001) in LS.

The addition of postbiotic could reduce the severity of pH decline in high non-structural carbohydrate rations and increase VFAs, however acidosis was not prevented.