Short-chain fatty acids in germfree mice and rats

The short-chain fatty acids (SCFAs) have been analyzed in small intestinal and cecal content of 10 germfree and six conventional mice from a Norwegian laboratory, in cecal content and serum of five germfree rats and two germfree mice from a Swedish laboratory and in Norwegian and Swedish autoclaved, nonpurified rodor diets. The mean total SCFA concentration was 1020 mumol/kg in cecum and 1010 mumol/kg in small intestine of Norwegian germfree mice; 124,600 mumol/kg in cecum and 6,250 mumol/kg in small intestine of conventional mice; 490 mumol/kg in cecum and 370 mumol/L in serum of Swedish rats; 360 mumol/kg in cecum and 290 mumol/L in serum of Swedish mice; 31.4 mmol/kg in Norwegian and 19.5 mmol/kg in Swedish nonpurified diets. Acetic acid accounted for more than 90% of the total concentration in all samples from germfree animals and diet, but detectable concentrations of propionic, isobutyric, n-butyric, isovaleric and n-valeric acid were also present. Thus, germfree animals have low, but measurable, concentrations of SCFAs in intestinal content compared to conventional animals. Most probably these acids originate mainly from the diet.