Nitrogen digestion of a large range of hays by mobile nylon bag technique (MNBT) in horses

Abstract

Nitrogen value of feeds depends on the proportion of feed nitrogen digested in the different compartments of the digestive tract, in particular the small intestine. in vivo and in sacco nitrogen digestibility of 21 hays with nitrogen content ranging from 0.76 to 3.07% N/DM was studied using the total faeces collection or MNBT. Five adult gelding (501 kg BW) were used for in vivo study. They were fed successively at maintenance experimental forages based-diet twice time a day at 8:00 and 16:30. Four adult gelding horses (487 kg BW) fitted with a permanent caecum canula were used for evaluation of digestibility of bags filled with experimental forages. They were fed at maintenance and received a ration composed of 70% hay and 30% barley in 2 equal meals a day (8:00 and 16:30). MRT of solid phase using mordanced chrome oxide, ingested at the beginning of the meal, and of bags, inserted in the stomach with a naso-oesophagal probe in the middle of the morning meal (after 1 kg of forage and before the rest of meal), was determined in a preliminary experiment using the four fistulated horses to check relative MRT of markers and bags. Then thirty nylon bags containing 200 mg of ground hay were inserted according to the same procedure. These were organised in 7 successive 4×4 latin squares where horses were fed three experimental hays and control hay during each period. Fifty two to 76% of bags were recovered in the caecum and the others in the faeces. DM digestibility in total tract measured in vivo and by MNBT were 50.8 and 51.9% respectively. True digestibility was estimated with both methods assuming that only dietary N reaching the faeces was N-NDF. Digestibility was corrected for MRT and bacterial N contamination for bags collected in the faeces. Digestibility was corrected for MRT and particle losses for bags collected in the caecum. Total tract true digestibility of N measured in vivo and by MNBT was 85.6% and 86.2% respectively. In the precaecal part in sacco true N digestibility was high 81.7%. It decreased when N-NDF/N ratio rose. The proportion of nitrogen digested in the small intestine averaged 87.6% and 75.6% when expressed in total percent digestible N intake or in percent of truly digestible N intake respectively.