摘要Glutathione(GSH)is widely found in animal cells and is essential for combating oxidative stress and inflammation.However,whether dietary GSH alleviates these processes in dairy cows remains un-known.The purpose of this research was to assess how supplementation with rumen-protected glutathione(RPG)influences oxidative stress,inflammation,and serum metabolites in transition dairy cows.One hundred multiparous Holstein cows(2.63±0.76 of parity,2.83±0.18 of body condition score,9388.53±1242.48 kg of previous 305-day milk yield,655.08±58.05 kg of body weight)were initially assigned to five treatment groups(n=20 per group)from a cohort of 3215 cows.After excluding cows with health disorders,50 healthy cows were randomly divided into five dietary treatment groups:control(basal diet,n=10),T1(basal diet+1.5 g/d RPG,n=10),T2(basal diet+2.0 g/d RPG,n=10),T3(basal diet+3.0 g/d RPG,n=10),and T4(basal diet+3.0 g/d GSH,n=10).Supplementation began approximately 21 days(±3)before the expected calving date and continued until 21 days postpartum.Blood samples were obtained at specific intervals(-21±3,-14±3,-7±3,0,7,14,and 21 days)to measure serum metabolic parameters associated with oxidative stress and inflammation.Milk composition analysis was conducted using samples collected on postpartum days 3,7,14,and 21.The results showed that RPG-supplemented cows(T1,T2,and T3)had greater serum GSH content compared with the control and T4 groups(P＜0.001),and greater serum catalase activity compared with the control group(P＜0.001).In contrast,levels of malondialdehyde,reactive oxygen species,haptoglobin,C-reactive protein,cortisol,and interleukin-6 were lower in RPG groups(P＜0.05).The optimal effect was observed at a dosage of 2.0 g/d RPG,while the 3.0 g/d GSH group had slightly better outcomes than the control group.The effects of 1.5 and 3.0 g/d RPG were similar,and no additional benefits were observed with higher dosages.Additionally,cows receiving 2.0 g/d RPG exhibited greater levels of serum glutathione peroxidase,total antioxidant capacity,and albumin/globulin ratio compared with control group(P＜0.05).RPG supplementation exhibited a quadratic change in somatic cell counts,fat-corrected milk yield,and feed efficiency,with somatic cell counts first decreasing and then increasing,while fat-corrected milk yield and feed efficiency first increasing and then decreasing(Pquadratic＜0.05).Metabolomic analysis of serum samples collected at-7(±3),+7,and+14 days relative to calving using liquid chromatography-mass spectrometry(LC-MS)revealed a total of 10 shared differential metabolites across the three time points.Compared with the control group,metabolomic profiles of T2 cows had greater levels of GSH and 5'-deoxyadenosine,while oxidized glutathione,cysteine,tetrahydrocortisol,superoxide anion,hydrogen peroxide,uric acid,prostaglandin,and glutamate were lower(P＜0.05).Overall,this study offers scientific evidence endorsing the application of RPG as a nutritional intervention in managing transition dairy cows.