本试验旨在探讨周期性变动饲粮蛋白质水平对内蒙古白绒山羊内源尿素氮循环和微生物蛋白质合成的影响。饲粮分为低(7.5%)、中(10.5%)和高(13.5%)3个蛋白质水平。选用9只体况良好,体重为(45.63±3.15) kg,装有瘤胃瘘管的内蒙古白绒山羊,采用单因子随机区组试验设计分为3组,即中蛋白质饲粮组(对照组)、变动低蛋白质饲粮组(2 d低蛋白质饲粮—2 d高蛋白质饲粮,循环饲喂)、变动高蛋白质饲粮组(2 d高蛋白质饲粮—2 d低蛋白质饲粮,循环饲喂)。预试期16 d,正试期12 d。通过全收粪尿法、嘌呤衍生物法和同位素灌注法测定山羊氮代谢、内源尿素氮循环以及微生物蛋白质合成的变化。结果表明：1)中蛋白质饲粮组与变动蛋白质饲粮组比较,瘤胃液氨氮(NH3-N)浓度显著增加(P<0.05),粪氮、尿氮排出量显著增加(P<0.05),沉积氮/摄入氮显著降低( P<0.05),尿中嘌呤衍生物排出量和微生物蛋白质合成的量显著降低( P<0.05)；2)变动低蛋白质饲粮组与变动高蛋白质饲粮组比较,瘤胃液NH3-N浓度显著降低( P<0.05)；3)周期性变动饲粮蛋白质水平后,进入胃肠道的尿素氮/肝脏合成的内源尿素氮显著增加(P<0.05),进入尿中的尿素氮/肝脏合成的内源尿素氮显著减少(P<0.05),返回鸟氨酸循环的尿素氮/进入胃肠道的尿素氮显著减少( P<0.05),用于再合成的尿素氮/进入胃肠道的尿素氮显著增加( P<0.05)。综上所述,周期性变动饲粮蛋白质水平有利于提高内蒙古白绒山羊氮利用率和微生物蛋白质合成量。%This experiment was conducted to study the effects of oscillating dietary protein levels on endoge-nous 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) , respec-tively. 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 low protein diet ( OSC-LPD, 2-day low protein diet—2-day high protein diet, oscillating fed) and oscillating high protein diet ( OSC-HPD, 2-day high protein diet—2-day low protein 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 micro-bial protein synthesis of goats were determined using total feces and urine collection, purine derivatives and iso-tope 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 signifi-cantly decreased in MPD group ( P<0.05) . 2) Compared with OSC-HPD, NH3-N concentration in rumen flu-id was significantly decreased in OSC-LPD group ( P<0.05) . 3) After fed oscillating protein diet, urea nitro-gen 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 u-rine ( UUE )/UER and urea nitrogen returned to ornithine cycle ( ROC )/GER were significantly decreased (P<0.05), and urea nitrogen re-used for anabolism (UUA)/GER was significantly increased (P<0.05). In conclusion, feeding oscillating protein level diet is benefit to improve the utilization of nitrogen and microbial protein synthesis.
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