MICROBIAL AMINO-ACID SYNTHESIS AND UTILIZATION IN RATS - THE ROLE OF COPROPHAGY

Four rats were housed in rages with mesh boors; another four rats were housed in tabular anti-coprophagy cages, in which they could not turn round to reach their own faeces. Both groups were fed for 6 d on a lo w-protein diet containing fermentable carbohydrates and (NH4Cl)-N-15. At the end of the experiment the rats were killed and their carcasses were homogenized, lysine was isolated by ion-exchange chromatography a nd its N-15 enrichment measured by isotope-ratio mass spectrometry. Th e N-15 enrichment in the lysine of the microbial fraction of faeces an d the total amount of lysine in the body were also determined in order to estimate the amount of microbial lysine absorbed. The N-15 enrichm ent in body lysine of non-coprophagic rats was not different from that previously measured in rats given unlabelled NH4Cl, but in coprophagi c rats it was significantly higher. The daily absorption of microbial lysine by the coprophagic rats accounted for 20.7 (SE 2.55) mg/kg body weight(0.75), but was only 0.5 (SE 1.04) mg/kg body weight(0.75) for the non-coprophagic rats. This value was not significantly different f rom zero. The utilization of microbial amino acids via coprophagy resu lted in a higher weight gain (adjusted for intake) in the coprophagic group (15.5 g/6 d) than in the non-coprophagic rats (3.1 g/6 d). It wa s concluded that, in rats, the utilization of microbial lysine occurre d exclusively via coprophagy.