Breath hydrogen concentrations of cats given commercial canned and extruded diets indicate gastrointestinal microbial activity vary with diet type.

Breath hydrogen (H(2)) concentration, an indicator of intestinal microbial abundance, was determined in cats given purified and commercial canned and dry-type diets. Before measurements, the cats were fed diets for more than 2 wk and habituated to a daily feeding interval of 4 hr. Breath H(2) concentrations were determined before a meal (approximately 25% daily MER) and then every 20 min for 8 hr or hourly for 10 hr. A clear rise above baseline breath H(2) concentrations, 1-2 ppm, was not observed in 6 males given a casein-based purified diet. A mean (+/- SEM) peak breath H(2) concentration of 22 +/- 4 ppm was observed in 6 other males, 6.3 hr after ingestion of a canned diet with protein, fat, and carbohydrate proportions similar to those of the purified diet. Area-under-the-curve (AUC) breath H(2) responses to the canned diet were substantially greater (p < 0.05) than responses observed in 5 males given a dry-type diet, but similar to responses observed in 12 males given an uncooked form of the canned diet. Gamma irradiation to inactivate microbes in the uncooked diet did not affect the breath H(2) response. Breath H(2) responses to 2 other canned and 2 other dry-type diets were evaluated in 8 adult females using a 4 x 4 Latin-square design. Peak and AUC responses to the canned diets were similar but approximately 2 times greater (p < 0.05) than responses to the dry diets. Relative to dry-type diets, canned diets induce a substantially greater breath H(2) production, and therefore appear to support a greater intestinal microbial population.