Effects of feeding Yucca schidigera extract in diets varying in crude protein and urea contents on growth performance and cecum and blood urea and ammonia concentrations of rabbits

Abstract

Yucca extract (YE) has ammonia-binding properties. It was hypothesized that by binding ammonia in the cecum, YE could influence cecal utilization of crude protein (CP) and dietary urea. Two experiments were undertaken using New Zealand White weanling rabbits (5–6 weeks of age). In both experiments, YE was mixed at 250 mg kg −1 of diet, and six individually fed rabbits were used per treatment. In Experiment 1, the four diets were: (1) high-protein (HP); (2) HP + YE (HPYE); (3) medium-protein (MP); (4) MP + YE (MPYE). The two protein levels were 23% and 19%. Average daily gain (ADG) was higher ( P < 0.01) in HPYE vs. HP whereas it was similar in MP vs. MPYE. There was no significant interaction between CP and YE. Feed intake was similar among treatments. Feed/gain in HPYE was better than in HP ( P < 0.05). Cecal urea-N (CUN), cecal ammonia-N (CAN) and cecal pH did not differ significantly among the four treatments. Plasma urea-N (PUN) concentrations differed among treatments ( P < 0.01). The PUN differed ( P < 0.05) between HP and MP treatments. The interaction of CP and YE was significant ( P < 0.01). The PAN was higher ( P < 0.05) for HP than for the other treatments. Cecal propionate was lower ( P < 0.05) for MP than for HP treatments. In Experiment 2, diets were: (1) low protein (LP); (2) LP + YE (LPYE); (3) LP + urea; (4) LPU + YE (LPUYE). The two CP treatments were 16.5% CP and 16.5% CP + 2% urea. The ADG was highest ( P < 0.05) for the LPYE, and was lower ( P < 0.05) for the LPU than for the LP treatments. CUN was similar among treatments, whereas CAN was lowest ( P < 0.05) in LPUYE. The PUN was higher ( P < 0.05) in the LPU than in the LP treatments, and was higher for LPU than for LPUYE. There were no differences in PAN. Cecal acetate and propionate concentrations were higher in LPYE than in the other groups, indicating a favorable effect of YE on cecal fermentation. It is concluded that YE modifies the utilization of dietary CP and urea by rabbits, by influencing cecal fermentation. This effect is probably mediated by ammonia binding.