Biochemical composition of feed ingredients influences equine gastric ecosystem activity in vitro

Abstract

When the pH of the gastric environment decreases below 4, acidity and volatile fatty acids (VFAs) can damage the epithelium. Depending on the feed ingredients incorporated in horse feeds, gastric ecosystem can be modified. Dehydrated alfalfa might be of interest because of its biochemical composition, which provides a strong acid buffering capacity. We ran an in vitro trial to assess the impact of three dehydrated alfalfas differing in biochemical composition on the persistence of acid buffering capacity over time in a gastric ecosystem undergoing fermentation. Barley and wheat bran were used for comparison.

Five substrates were prepared from 0.5 g dry matter (DM) barley, completed with 0.5 g DM alfalfa, wheat bran, or barley. Substrates were added to a modified Lowe culture medium in bottles under sterile conditions. After inoculation with gastric contents collected from horses, the bottles were incubated anaerobically for 10-hours. Every two hours, the gas produced, the concentration of VFAs and lactate, the pH, and the amount of 0.1 M hydrochloric acid (HCl) required to decrease the pH of the solution down to 4 were measured in triplicate.

The pH of the feed ingredients was close (5.81 −6.29), but 7 −12 times more HCl was needed to bring the pH down to 4 with alfalfa compared to barley, and 3 −5 times more compared to wheat bran. This acid buffering capacity was correlated with ash content (r = 0.984; P = 0.002), and particularly calcium content (r = 0.995; P < 0.001). Fermentations started faster in bottles containing alfalfa (P < 0.001 after 2 h), but then gas production was higher with barley and wheat bran (P < 0.001). However, VFA concentrations remained higher with alfalfa than other substrates (P < 0.05), and the higher the content in proteins and simple sugars the more pronounced the differences. While the pH of the solution and the amount of HCl required to decrease to pH4 fell sharply over the 10-hour monitoring period, these variables remained higher with alfalfa compared to barley and wheat bran substrates (P < 0.001 after 6-hours for pH; P < 0.05 after 4-hours for HCl amount). Despite their different biochemical composition, the impact of the three alfalfas in the environment was close. These results suggest that adding alfalfa to feeds could contribute maintaining a higher pH in the horse stomach. This seems to arise from intrinsic high acid buffering capacity of alfalfa, rather than from the reduction in gastric fermentations. Considering the acid buffering capacity of feed ingredients in the formulation of horse feed could help maintain a physiological gastric pH for longer and reduce gastric diseases.