Dietary lactose and the metabolic activity of the caecal microfloras of weanling and adult rats.

Weanling or adult (9 wk old) rats were fed diets containing 0, 250 or 500 g lactose/kg for 10 days, after which the activities of six caecal microbial enzymes (azoreductase, beta-glucosidase, beta-glucuronidase, nitrate reductase, nitroreductase and urease) were determined. Adult controls had larger caeca than weanlings, but the numbers of bacteria were not significantly different. Expressed in relation to body weight, caecal microbial enzyme activities were significantly lower in adult controls, with the exceptions of beta-glucuronidase and urease. Lactose caused caecal enlargement; this was greatest in weanling animals, which also showed a decreased concentration of bacteria. Lactose increased total nitrate reductase and urease activities in both age groups, but decreased total azoreductase and nitroreductase activities in weanlings. Enzyme activities per 10(9) bacteria were decreased for azoreductase, beta-glucosidase, beta-glucuronidase and nitroreductase in both age groups, while urease activity increased. Azoreductase and nitroreductase activities were highly correlated but nitrate reductase and urease did not correlate significantly with any other enzyme activity.