摘要This study was to evaluate how low phosphorus(P)diets affect growth performance and fecal P excretion in Xia-Nan cattle and to elucidate the underlying mechanisms.Thirty-two healthy Xia-Nan bulls with similar body weights(BW;267.42±45.77 kg)were assigned to four groups with eight in-dividual replicate pens per group in a completely randomized block design,stratified by initial BW and average dry matter intake(DMI).Cattle were fed total mixed rations(concentrate-to-forage ratio 40:60)with varying dietary P levels(DM basis):0.16％(XPA),0.19％(XPB),0.22％(XPC),and 0.25％(XPD;control)for 90 d.The first three groups were considered low-P treatments.Compared with the XPD group,XPA showed significantly lower average daily gain(ADG;P=0.018)and DMI(P=0.046),while XPB and XPC showed no differences(P＞0.05).XPB group showed a significant lower feed conversion ratio(FCR)than XPA(P=0.049)and had the lowest FCR among all groups.Total-tract apparent digestibility of calcium(Ca;P=0.006)and P(P=0.006)decreased linearly with dietary P reduction.P intake(P＜0.001)and fecal P content(P＜0.001)were significantly lower in low-P groups than in the XPD group and decreased linearly with P reduction.Serum concentrations of parathormone hormone(PTH;P＜0.001),1,25-dihydroxyvitamin D3(1,25(OH)2D3;P=0.005),Ca(P＜0.001),and P(P＜0.001)were positively correlated with decreasing dietary P levels,whereas calcitonin(CT;P=0.016)and alkaline phosphatase(ALP;P=0.006)were negatively correlated.XPB and XPD groups had higher molar proportions of propionate(P＜0.001)and butyrate(P=0.006)but lower acetate molar proportion(P＜0.001)and acetate-to-propionate ratio(P＜0.001)than XPA.Fecal P excretion correlated positively with Rumino-coccaceae_UCG-005,Saccharofermentans,and Butyrivibrio,and negatively with Rikenella-ceae_RC9_gut_group and uncultured_bacteriumf_F082.These results suggest that reducing dietary P to 0.19％(XPB)maintained optimal growth performance while reducing environmental P pollution in Xia-Nan cattle.