Cholesterol and bile acid metabolism as influenced by dietary and environmental manipulations of the intestinal microflora in swine

Nineteen Duroc pigs which were obtained by hysterectomy were raised in five isolators to six weeks of age. Four of the five groups were inoculated with L. acidophilus and all groups were maintained on a 0.5% cholesterol milk formula diet. During this time serum cholesterol levels were 1000 mg. % ± 200. The bile acid composition of the feces collected at six weeks was principally hyocholic acid and chenodeoxycholic acid, which were the primary bile acids produced by the liver. Secondary bile acids formed from the primary acids by microbial dehydroxylation and oxidation were found only in trace amounts at 6 weeks. These small amounts of bacterial metabolites indicated minor microbial contamination which was confirmed by standard microbiological techniques. Small numbers of organisms other than Lactobacillus were found. No metabolism of hyocholic acid or hyodeoxycholic acids by these microorganisms could be detected in vitro at that time. At 6 weeks of age, 2 of the 5 groups were removed from the isolators and placed in a non-sterile environment. One of these groups continued to receive the milk formula and the other was weaned to a pig starter ration containing 0 .5% cholesterol. The other three groups remained in the isolators and received either the pig starter or the formula diet. When the two groups were taken from the isolators, they developed a complete microbial flora with Lactobacillus sp., Enterococcus, E. coli, slow lactose fermenters, and Staphylococcus predominating. At the same time the microflora increased in numbers and types in these groups, the serum cholesterol levels dropped dramatically to about 100 mg. % at 9 weeks of age. Also, the relative amounts of microbial metabolites of the bile acids, primarily hyodeoxycholic acid, increased in the feces and bile, and the metabolism of hyocholic acid in vitro by the fecal microorganisms was enhanced.