Estimation of the proportion of bacterial nitrogen in canine feces using diaminopimelic acid as an internal bacterial marker.

A bacterial marker can be used to determine the portion of fecal N that is of bacterial origin, as well as the effect of dietary factors on the bacterial N in feces of the dog. Two experiments were conducted to determine the efficacy of diaminopimelic acid (DAPA) and purines as bacterial markers in dogs. In Exp. 1, five adult female dogs were fed the same commercial diet. In Exp. 2, 50 dogs were fed one of four test diets (as-fed basis): a prebiotic-free control or diets containing either 1% chicory, 1% mannanoligosaccharide (MOS), or 1% chicory plus 1% MOS. Fresh feces were collected in both experiments and used to isolate a bacteria-rich sample (BRS) by differential centrifugation. In Exp. 1, the BRS had a N:purine ratio of 0.66 and N:DAPA ratio of 18.9. The CV for the N:purine ratio (20.7%) was much higher than that for the N:DAPA ratio (6.1%), indicating that DAPA resulted in a less variable estimate of fecal bacterial N. Using either marker, approximately 50% of the fecal N was estimated to be of bacterial origin. In Exp. 2, the N:DAPA ratio of the BRS did not differ (P = 0.14) among treatments. The BRS from dogs fed prebiotic-containing diets had treatment averages for N:DAPA ratios ranging from 16.9 to 18.5, whereas BRS from dogs fed the control diet had a ratio of 15.9. Averaged across all dogs, approximately 46% of fecal N was of bacterial origin. When calculating fecal bacterial concentrations using the average N:DAPA ratio for all dogs, little difference existed in the estimation compared with using individual values. The value resulting from use of the average ratio was approximately 13% higher than when using the individual ratios for dogs fed the control diet, which was due to the lower N:DAPA ratio for dogs fed the control diet compared with dogs fed the other treatments. Based on the consistency of the N:DAPA ratio of the BRS, DAPA seems to be a suitable marker for estimation of bacterial N in the feces of dogs.