Experimental feed induction of ruminal lactic, propionic, or butyric acidosis in sheep.

A study was conducted to determine the feasibility to induce rumen acidosis with propionate, butyrate, or lactate as the major fermentation end products. Three rumen-cannulated Texel wethers were used in a 3 x 3 Latin square design. Each period consisted of 11 d of adaptation where wethers were daily fed at 90% of ad libitum intake a hay and wheat-based concentrate diet (4:1 ratio on a DM basis) in 2 equal portions followed by 3 d of acidosis induction. During the challenge, the morning feeding was replaced by an intraruminal supply of wheat (readily fermentable starch), corn (slowly fermentable starch), or beet pulp (easily digestible fiber), dosed at 1.2% of BW. Ruminal liquid samples were taken daily 1 h before (-1) and 1, 3, 5, and 6 h after intraruminal feed supply to measure pH, VFA, and lactic acid concentration. The differences between treatments accentuated throughout the 3-d challenge, being maximal and significant on d 3. Indeed, 6 h after the third day of the challenge, mean ruminal pH was less for wheat (4.85) than for corn (5.61; P = 0.008) and beet pulp (6.09; P = 0.001), and total VFA tended to be less for wheat (48.7 mM) than for corn and beet pulp (84.7 mM on average; P = 0.08). At the same time, the proportion of acetate was greater for wheat than for corn (75.5 and 62.2%, respectively; P = 0.005) but did not differ from beet pulp challenge (69.0%). The proportion of propionate was greatest for beet pulp compared with corn and wheat (21.0, 17.3, and 12.1%, respectively; P = 0.03), whereas the butyrate proportion was greatest for corn, intermediate for wheat, and least for beet pulp (16.3, 10.8, and 8.3%, respectively; P = 0.05). Lactate concentration was greatest for wheat (45.5 mM) compared with corn and beet pulp (8.3 mM on average; P = 0.01). Under our experimental conditions, ruminal lactic acidosis was successfully induced by wheat, whereas butyric and propionic subacute ruminal acidosis were respectively provoked by corn and beet pulp. We developed an original model that promoted differentiated fermentation pathways in the rumen of sheep. It will be used to study the ruminal microbiome changes involved in different acidosis situations.