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Gastrointestinal Content and Mucosal Oxidation of Volatile Fatty Acids in Sheep¹

Purdue University, Lafayette, Indiana

Abstract

Ingesta volumes, total VFA and VFA ratios were determined in the rumen, omasum, abomasum, caecum and anterior colon of sheep fed either roughage or concentrate rations. The relative rates of VFA oxidation and oxygen uptake by ruminal and caecal epithelial tissue were compared in vitro.

The concentration of total VFA per liter of ingesta in the rumen, omasum, caecum and colon was similar. However, the greatest quantity of VFA was in the rumen because of its relatively larger volume. VFA ratios were similar in the rumen-reticulum, omasum and abomasum, but differed (P<.01) from the VFA ratios in the caecum and colon. The molar percent of acetate was higher (P<.01) in the caecum, and the molar percent of propionate and butyrate was lower (P<.01) in the caecum than in the rumen.

Ruminal ingesta volumes in the roughage-fed sheep were higher (P<.01) than in the concentrate-fed sheep, whereas the caecal ingesta volumes were similar between sheep fed the two diets. The concentrate-fed sheep had a higher (P<.05) concentration of VFA in the caecum than did the roughage-fed sheep, but this difference did not occur in the rumen. Sheep fed a concentrate ration had a greater (P<.01) molar percent of butyrate in the rumen and caecum than sheep fed a roughage ration, but there were no differences in acetate due to the ration.

Rumen epithelium oxidized more (P<.05) total VFA than the caecal epithelium. The caecal tissue had a greater (P<.01) preference for acetate, while the ruminal tissue had a greater (P<.01) preference for butyrate.

Oxygen uptake was lower (P<.01) for caecal mucosa than for rumen mucosa when these tissues were incubated in the absence or presence of exogenous VFA. However, there were no significant differences in oxygen uptake of excised tissues due to ration.

¹ Contribution from the Department of Biochemistry, Purdue University, Lafayette, Indiana, as Journal Paper No. 2562.

² Recipient of a National Institutes of Health Biochemistry Graduate Traineeship during this study.