Energy available to the sow from microbial fermentation in the large intestine. Effect of feeding diets with and without Levucell SB.

In pigs, energy derived from the diet is digested in the small intestine through enzymatic hydrolysis or fermented in the large intestine by micro-organisms. In growing animals, hindgut fermentation accounts for 8 to 18% of total dietary energy, increasing with non starch polysaccharides (NSP) levels. Sow diets are higher in fibre than pig diets, but little is known about hindgut fermentation in sows.

A trial was designed to test hypothetic mode of action of Levucell SB (LSB) on fibre fermentation : through decreased redox potential, LSB would favor the cellulolytic microflora, thus increase fibre fermentation, possibly change short chain fatty acids (SCFA) production and gases, with less methane produced through fermentation shift to acetogenesis.

A trial was set-up at the Faculty of Agricultural Science in Foulum (DK) : 16 sows were surgically fitted with a T-canula at ileo-caecal junction. They were affected to 4 dietary treatments, corresponding to diets based on one of 2 fibre sources (sugar beet pulp , SBP or wheat bran, WB), with or without addition of LSB.

Sows received the diet for 3 weeks prior digesta collection, starting with faeces during 3 days then ileal juices for 2 days. Ileal juices were freeze-dried after collection. The samples

were incubated for 48h with faeces from the same sow under anaerobic condition to simulate hindgut fermentation. At the end of the trial, sows were slaughtered and digestive content was sampled at different locations. They were analyzed and their evolution over 4 h under anaerobic conditions was followed-up.

Ileal and faecal digestibilities of dietary NSP were affected by fibre source (SBP>WB).

LSB did not affect the digestibility, except total tract digestibiilty of crude protein (little physiological significance). Ileal juices composition was affected by LSB : less formiate, more propionate. WB yielded more lactate than SBP. SCFA in faeces composition were not affected by dietary treatment. During in vitro incubation, pH and redox potential variations did not depend on treatment. Fibre source impacted slightly the lactic acid bacteria counts (faster growth with SBP) and yeast (higher counts with WB). SCFA production depended on fibre source but not LSB.

Samples collected at slaughter showed significant differences in pH in proximal colon and distal colon, due to combination of fibre source and LSB. Redox potential differed in mid and distal colon due to fibre source (WB>SBP). More methane and SCFA were released within 4 h from colonic sample with SBP.

The trial did not confirm the hypothesis for the mode of action of LSB. Further knowledge will be derived from improvement in the protocol (influence of freeze-drying on SB counts; simulation of the anaerobic status in the large intestine) and revision in the hypothetical mode of action.