[Objectives]This study was conducted to evaluate the rumen slow-release effect of coated urea by techniques of in vitro batch culture,in vivo rumen infusion,and continuous artificial rumen simulation system.[Methods]In vitro batch culture:one common urea and four commercial coated slow-release urea were added to in vitro ruminal cultures in quadruplicate.Culture samples were collected at 0,1,3,6,9,12,24 h for determination of ammonia concentration,and to evaluate the slow-release effect of different coated urea.Coated urea with the best slow-release effect was selected for further evaluation.In vivo rumen infusion:twelve fatting male Hu sheep(mean body weight 27.6 kg)with rumen cannula were randomly assigned to two treatments,and infused with 0.5%(dry matter intake,DMI)of common urea or 0.55%of coated urea respectively.Rumen fluid samples were collected to measure ammonia concentration and pH value.Continuous artificial rumen simulation experiment:three fermenters were assigned to one of three experiment diets:basal diet supplemented with 3.5%soybean meal(BSM),basal diet supplemented with 0.5%common urea(CU),and basal diet supplemented with 0.55%coated slow-release urea(SRU)respectively.The energy deficiency in CU and SRU group was supplemented with ground corn.The rumen simulation system with three fermenters was used in three replicated periods of 7 d each(4 d for adaptation and 3 d for sampling).Fermenter liquid and overflow liquid were collected at different time points after mooning feeding to determine fermentation parameters and microbial protein concentration.[Results]The results of in vitro batch culture showed that the ammonia concentration of slow-release urea A was lower than common urea and three other coated urea at 9 and 12 h after fermentation(P<0.05).In vivo rumen infusion experiment:compared with common urea group,the ammonia concentration and pH value were greatly reduced in slow-release urea at 1 h after infusion(P<0.05).While the pH value in slow-release urea was significantly higher than that in common urea at 6 h after infusion(P<0.05).Continuous rumen simulation experiment:slow-release urea addition significantly increased propionic acid and microbial protein concentration compared with the other two groups(P<0.05),and decreased the pH value compared with urea group(P<0.05).[Conclusions]This study demonstrated that the slow-release effect of different coated urea was different,and slow-release urea A had the best rumen slow-release effect.The slow-release urea screened by in vitro batch culture also showed good slow-release effect under the condition of in vivo rumen infusion.Diets with slow-release urea A supplementation could improve rumen fermentation and increase microbial protein synthesis in rumen continuous simulation system,but its release effect needs to be further verified by animal feeding experiment.
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