Utilization of dietary urea nitrogen is stimulated by D-mannitol feeding in rabbits

The effect of D-mannitol as an indigestible sugar on apparent digestibility of nutrients, nitrogen (N) utilization and growth performance, have been investigated in growing rabbits fed a urea-containing diet. In experiment 1, 40-day-old male rabbits were fed a commercial diet with urea 10g/kg with added glucose or D-mannitol 60g/kg each. Thereafter, in experiment 2 the rabbits aged 55days were fed a commercial diet with or without urea 10g/kg. Feed restriction at 55g/kg^0.75/day was carried out in both experiments. Addition of D-mannitol to the urea-containing diet decreased urinary N excretion, which consequently increased N retention and ratios of retained N to consumed N or apparently absorbed N. Addition of urea alone to the diet increased daily N intake and urinary N excretion but did not affect N retention. Weight gain and feed efficiency were improved by D-mannitol feeding, whereas feeding with urea alone did not affect these parameters. Utilization of dietary urea was enhanced in growing rabbits fed the urea-containing diet with D-mannitol, resulting in improvement of N retention and growth performance.