Dietary carbohydrates affect caecal fermentation and modify nitrogen excretion patterns in rats II. Studies with diets differing in protein quality

In 2 two-factorial experiments, each conducted on 80 growing male rats, the effects of substituting 10% raw potato starch (PS), pectins (PEC), or cell ulose (CEL) for wheat starch (WS) and the addition of tannic acid to WS (WS TA) were studied using diets differing in protein quality. Casein unsupplem ented or supplemented with DL-methionine and gluten unsupplemented or suppl emented with lysine, methionine and tryptophan were used as protein sources in Experiment 1 and 2, respectively. Parameters indicative of caecal ferme ntation intensity (pH, acetic, propionic and butyric acid contents, digesta and tissue weight) and of protein metabolism (urea blood concentration, fa ecal and urinary nitrogen excretion) were determined. Ten-day balance exper iments were preceded by a 10-day adaption period to respective carbohydrate s given in a diet containing balanced protein. In both experiments the type of carbohydrates affected the caecal concentra tion of individual and total SCFA and other parameters of fermentation inte nsity. Pectins and potato starch were fermented more intensively than cellu lose. Faecal N excretion was increased by all carbohydrates substituted for cereal starch, and by tannic acid. Urinary excretion was greater on CEL th an on PEC and WSTA containing casein and on other diets containing gluten. In both experiments urinary N excretion was the lowest on PEC diets. Protei n quality had the greatest effect on apparent biological value and net prot ein utilization but all indices of protein utilization were also affected b y carbohydrates. It is concluded that not only the amount of N excreted in faeces but also in urine is affected by the type and fermentability of carb ohydrates.