[1] KIRAN D,MUTSVANGWA T.Nitrogen utilization in growing lambs fed oscillating dietary protein concentrations[J].Animal Feed Science and Technology,2009,152(1/2):33-41.
[2] COLE N A,GREENE L W,MCCOLLUM F T,et al.Influence of oscillating dietary crude protein concentration on performance,acid-base balance,and nitrogen excretion of steers[J].Journal of Animal Science,2003,81(11):2660-2668.
[3] MUSCHER A S,SCHRÖDER B,BREVES G,et al.Dietary nitrogen reduction enhances urea transport across goat rumen epithelium[J].Journal of Animal Science,2010,88(10):3390-3398.

[4] ALDERMAN G,COTTRILL B R.Energy and protein requirements of ruminants[S].Wallingford:CAB International,1993.
[5] 李玫.美国Feedstuffs饲料成分分析表(2007版)[J].饲料广角,2007(12):37-40.
[6] 杨胜.饲料分析及饲料质量检测技术[M].北京:北京农业大学出版社,1993.
[7] 杜建文.不同日粮对内蒙古白绒山羊消化道
UT-
B表达的影响研究[D].硕士学位论文.呼和浩特:内蒙古农业大学,2010.
[8] SARRASECA A,MILNE E,METCALF M J,et al.Urea recycling in sheep:effects of intake[J].The British Journal of Nutrition,1998,79(1):79-88.

[9] LOBLEY G E,BREMNER D M,ZUUR G.Effects of diet quality on urea fates in sheep as assessed by refined,non-invasive [
15N
15N] urea kinetics[J].The British Journal of Nutrition,2000,84(4):459-468.
[10] CHEN X B,GOMES M J.Estimation of microbial protein supply to sheep and cattle based on urinary excretion of purine derivatives-an overview of the technical details[J].International Feed Resources Unit,1992:1-19.
[11] ORELLANA-BOERO P,SERADJ A R,FONDEVILA M,et al.Modelling urinary purine derivatives excretion as a tool to estimate microbial rumen out ow in alpacas(
Vicugna pacos)[J].Small Ruminant Research,2012,107(2/3):101-104.
[12] CHEN X B,ØRSKOV E R.Research on urinary excretion of purine derivatives in ruminants:past,present and future[M]//Estimation of microbial protein supply in ruminants using urinary purine derivatives.Netherlands:Springer,2004:180-210.
[13] CARRO M D,CANTALAPIEDRA-HIJAR G,RANILLA M J,et al.Urinary excretion of purine derivatives,microbial protein synthesis,nitrogen use,and ruminal fermentation in sheep and goats fed diets of different quality[J].Journal of Animal Science,2012,90(11):3963-3972.

[14] 韩正康,陈杰.反刍动物瘤胃的消化和代谢[M].北京:科学出版社,1988.
[15] SATTER L D,SLYTER L L.Effect of ammonia concentration on rumen microbial protein production in vitro[J].The British Journal of Nutrition,1974,32(2):199-208.

[16] FIRKINS J L,YU Z,MORRISON M.Ruminal nitrogen metabolism:perspectives for integration of microbiology and nutrition for dairy[J].Journal of Dairy Science,2007,90(Suppl.1):E1-E16.
[17] COLMENERO J J O,BRODERIC G A.Effect of dietary crude protein concentration on milk production and nitrogen utilization in lactating dairy cows[J].Journal of Dairy Science,2006,89(5):1704-1712.

[18] IPHARRAGUERRE I R,CLARK J H,FREEMAN D E.Varying protein and starch in the diet of dairy cows.Ⅰ.Effects on ruminal fermentation and intestinal supply of nutrients[J].Journal of Dairy Science,2005,88(7):2537-2555.

[19] CASTILLO A R,KEBREAB E,BEEVER D E,et al.A review of efficiency of nitrogen utilisation in lactating dairy cows and its relationship with environmental pollution[J].Journal of Animal and Feed Sciences,2000,9:1-32.
[20] YAN T,FROST J P,AGNEW R E,et al.Relationships among manure nitrogen output and dietary and animal factors in lactating dairy cows[J].Journal of Dairy Science,2006,89(10):3981-3991.

[21] REYNOLDS C K,KRISTENSEN N B.Nitrogen recycling through the gut and the nitrogen economy of ruminants:an asynchronous symbiosis[J].Journal of Animal Science,2008,86(Suppl.14):E293-E305.
[22] LUDDEN P A,PAS,WECHTER T L,et al.Effects of oscillating dietary protein on growth,efficiency,and serum metabolites in growing beef steers[J].Professional Animal Scientist,2003,19(1):30-34.
[23] ERICKSON G E,KLOPFENSTEIN T J.Nutritional methods to decrease N losses from open-dirt feedlots in Nebraska[J].The Scientific World Journal,2001,1(S2):836-843.
[24] COLE N A,CLARK R N,TODD R W,et al.Influence of dietary crude protein concentration and source on potential ammonia emissions from beef cattle manure[J].Journal of Animal Science,2005,83(3):722-731.
[25] LUDDEN P A,WECHTER T L,HESS B W.Effects of oscillating dietary protein on nutrient digestibility,nitrogen metabolism,and gastrointestinal organ mass in sheep[J].Journal of Animal Science,2002,80(11):3021-3026.
[26] ARCHIBEQUE S L,FREETLY H C,FERRELL C L.Net portal and hepatic flux of nutrients in growing wethers fed high-concentrate diets with oscillating protein concentrations[J].Journal of Animal Science,2007,85(4):997-1005.
[27] LAPIERRE H,LOBLEY G E.Nitrogen recycling in the ruminant:a review[J].Journal of Dairy Science,2001,84 (Suppl.):E223-E236.
[28] DORANALLI K,PENNER G B,MUTSVANGWA T.Feeding oscillating dietary crude protein concentrations increases nitrogen utilization in growing lambs and this response is partly attributable to increased urea transfer to the rumen[J].The Journal of Nutrition,2011,141(5):560-567.