摘要Arginine(Arg)can potentially increase milk yields in early lactating dairy cows by stimulating the development of mammary gland and the biosynthesis of milk proteins and fatty acids(FA);however,the underlying mechanism is still unclear.The hypothesis that rumen-protected Arg addition would increase milk,milk fat,and milk protein yields was tested,aiming to dlucidate the possible mechanism.Forty-eight multiparous Chinese Holstein dairy cows(milk yield 34.9±1.27 kg/d,body weight 658±12.7 kg,and days in lactation[DIL]16.4±2.56)were selected on the principle of proximity and blocked by DIL and milk yield,and divided into one of four groups in a randomized block design:control(without RPArg),low RPArg(LRPArg;20 g/d Arg),medium RPArg(MRPArg;40 g/d Arg),and high RPArg(HRPArg;60 g/d Arg),4 replicates per group and 3 cows per replicate and the experiment duration was 95 days,including a 10-d covariate period,a 15-d adaptation period,and a 70-d sampling period.The production of actual milk,energy-corrected milk,fat-corrected milk,milk fat,and milk protein linearly increased(P＜0.05)with RPArg provision.The yields of de novo FA and mixed FA in the milk linearly increased(P＜0.01),but that of preformed FA linearly decreased(P=0.007).Supplementation with RPArg linearly increased the daily production of Arg,Asp,Cys,Glu,His,Met,Phe,Ser,Thr,and Trp(P＜0.05).With RPArg provision,serum contents of glucose,albumin,total protein,and nitric oxide linearly increased(P＜0.05);the levels of estradiol,prolactin,and insulin-like growth factor 1 quadratically increased(P＜0.01);and that of blood urea nitrogen quadratically decreased(P=0.023).Furthermore,supple-mentation with 40 g/d Arg from RPArg promoted the expression of proteins implicated in mammary gland proliferation,FA synthesis,and milk protein synthesis.Thus,RPArg addition enhanced milk pro-duction,FA synthesis,and milk protein synthesis by promoting the expression of proteins involved in mammary gland development,FA synthesis,and milk protein synthesis.