Effect of different physical processing methods of feces samples on the fecal nitrogen obtained in sheep fed with increasing dietary protein content

Abstract

Volatile loss of nitrogen as ammonia, especially from fecal samples, can occur during collection and analysis, and may overestimate nitrogen (N) retention in ruminants. Thus, we hypothesized that the amount of unaccounted fecal N that is lost during pre-drying influence nitrogen balance and N retention estimate in sheep, regardless the dietary crude protein (CP) content. Thus, our objective was to evaluate the effect of different methods of physical processing of fecal samples on the quantification of fecal N, and the effect of this loss on nitrogen balance and N retention in sheep fed increasing CP content in the diet. Thirty-two non-castrated male Santa Inês lambs with three months of age and similar initial body weights (BW 20 ± 1kg) were used. The animals were fed with four diets with different CP contents [120, 140, 160 and 180 g CP/kg of dry matter (DM)]. Samples of feces were collected, stored and physically processed according to four treatments (Wet, Dried, Frozen-wet (FR-wet) and Frozen-dried (FR-dried) and the nitrogen balance was determined. Animals fed with 120, 160 and 180g of CP/kg DM presented higher fecal N amount in the wet samples when compared to the dried samples (P<0.05). The physical processes did not affect the N amount quantified in fecal samples from the animals fed with 140 CP/kg DM (P>0.05). The physical processes affected ammonia N quantified in feces from animals fed with all the diets [120, 140, 160 and 180 g CP/kg DM (P<0.05)]. The dried treatment showed the lowest ammonia N when compared with wet, FR-wet and FR- dried treatments, respectively, in all the diets (P<0.05). The absorbed N, retained N, the retained N in relation to N intake, and retained N in relation to absorbed N were affected (P<0.05) by the physical processes within all the CP contents evaluated. The pre-drying causes loss of N in fecal samples of animals fed diets with the required CP content (120, 160 and 180 g/kg DM), especially after freezing. The lost fecal N influence nitrogen balance and N retention estimated in sheep.