Effects of Oscillating Dietary Protein Levels on Endogenous Urea Nitrogen Recycling and Microbial Protein Synthesis of Inner Mongolia White Cashmere Goats

This experiment was conducted to study the effects of oscillating dietary protein levels on endogenous urea nitrogen recycling and microbial protein synthesis of Inner Mongolia white cashmere goats.There were three levels of dietary protein,which were 7.5%(low),10.5%(medium) and 13.5%(high),respectively.Nine healthy Inner Mongolia white cashmere goats [(45.53 ± 3.15) kg] fitted with ruminal cannulas were blocked into 3 groups in a one-factor random block design.Goats in different groups were fed consisted medium protein diet(MPD,control group),oscillating lowprotein diet(OSC-LPD,2-day lowprotein diet—2-day high protein diet,oscillating fed) and oscillating high protein diet(OSC-HPD,2-day high protein diet—2-day lowprotein diet,oscillating fed).The pre-experimental period lasted for 16 days,and the experimental period lasted for 12 days.The changes of nitrogen metabolites,endogenous urea nitrogen recycling and microbial protein synthesis of goats were determined using total feces and urine collection,purine derivatives and isotope infusion methods.The results showed as follows: 1) compared oscillating protein diet groups,ammonia nitrogen(NH3-N) concentration in rumen fluid was significantly decreased(P 0.05),urea nitrogen and fecal nitrogen excretions were significantly increased(P 0.05),nitrogen retention/nitrogen intake was significantly decreased(P 0.05),and urinary excretion of purine derivatives and microbial protein synthesis were significantly decreased in MPD group(P 0.05).2) Compared with OSC-HPD,NH3-N concentration in rumen fluid was significantly decreased in OSC-LPD group(P 0.05).3) After fed oscillating protein diet,urea nitrogen recycling to the gastrointestinal tract(GER)/urea nitrogen endogenous produced in liver(UER) and urea nitrogen re-used for anabolism(UUA)/GER were significantly increased(P 0.05),urea nitrogen loss to urine(UUE)/UER and urea nitrogen returned to ornithine cycle(ROC)/GER were significantly decreased(P0.05),and urea nitrogen re-used for anabolism(UUA)/GER was significantly increased(P0.05).In conclusion,feeding oscillating protein level diet is benefit to improve the utilization of nitrogen and microbial protein synthesis.