This experiment was conducted to study the effects of different combinations of rumen?protected me?thionine ( RPMet) and rumen?protected lysine ( RPLys) on rumen microbial protein production, lactation per?formance and nitrogen excretion of dairy cows. Forty Holstein lactating dairy cows with similar age, body weight, parity, milk yield, milk composition and lactation period were randomly divided into 10 groups with 4 cows per group. Cows in the control group were fed a basal diet, and cows in experimental groups were fed di?ets supplemented with different levels of RPMet [ 22.5 ( L) , 25.0 ( M) and 27.5 g/( d·head) ( H) ] and RPLys [27.5 ( L) , 30.0 ( M) and 32.5 g/( d·head) ( H) ]. A total of 9 experimental groups were de?signed, which were named as LL, ML, HL, LM, MM, HM, LH, MH and HH ( first letter indicated RPMet supplemental level, and the second letter indicated RPLys supplemental level) , respectively. The pre?experi?ment lasted for 15 days, and the experiment lasted for 60 days. The results showed as follows: 1) in terms of rumen microbial protein production, the experimental groups were improved compared with the control group, and MM, HM groups were significantly higher than the control group ( P＜0.01). 2) In terms of milk yield, the experimental groups were significantly higher than the control group ( P＜0.01) , MM group was the high?est, and increased by 18.61%. 3) In terms of milk component, the milk fat percentage of experimental groups was improved compared with the control group, and LM, HM and MM groups were significantly higher than the control group ( P＜0.01) ; the milk protein percentage in experimental groups was improved compared with the control group, and MM, HL, LM, ML, HH, HM and LH groups were significantly higher than the con?trol group ( P＜0.01) ; the milk somatic cell count in experimental groups was decreased compared with the control group, and MH, MM, HL, LH and LM groups were significantly lower than the control group ( P＜0.01). 4) In terms of nitrogen total excretion, the experimental groups were significantly lower than the con?trol group ( P＜0.01) , and the MM group was the lowest, and reduced by 11.00%. The feces nitrogen and u?rine nitrogen in MM group were significantly lower than those in the control group ( P＜0.01) , and the nitrogen apparent digestibility and nitrogen deposition in MM, MH and HL groups were significantly higher than those in the control group ( P＜0.01). In combination with various test indicators, the 25.0 g/( d·head) RPMet+30.0 g/( d·head) RPLys is the best combination.[ Chinese Journal of Animal Nutrition, 2019, 31 ( 6 ) :2716?2726]%本试验旨在研究过瘤胃蛋氨酸( RPMet)与过瘤胃赖氨酸( RPLys)不同组合对奶牛微生物蛋白产量、产奶性能和氮排泄的影响.选取年龄、体重、胎次、产奶量、乳成分及泌乳期相近的荷斯坦奶牛40头,随机分为10个组,每组4头.对照组饲喂基础饲粮,试验组添加不同水平的RPMet和RPLys. RPMet设置3个梯度,添加水平分别为22.5( L)、25.0( M)、27.5 g/( d·头) ( H) ;RPLys设置3个梯度,添加水平分别为27.5( L) 、30.0( M) 、32.5 g/( d·头) ( H) ,共组成9个不同组合,分别为LL、ML、HL、LM、MM、HM、LH、MH、HH组(第1个字母为RPMet添加水平,第2个字母为RPLys添加水平) .预试期15 d,正试期60 d.结果表明:1)在瘤胃微生物蛋白产量方面,各试验组与对照组相比均有所提高,其中 MM、 HM 组极显著高于对照组( P＜0.01) . 2)在产奶量方面,各试验组均极显著高于对照组( P＜0.01) ,其中以MM组最高,提高幅度达18.61%. 3)在乳成分方面,各试验组乳脂率与对照组相比均有所提高,LM、HM、MM组极显著高于对照组( P＜0.01);各试验组乳蛋白率与对照组相比均有所提高,MM、HL、LM、ML、HH、HM、LH组极显著高于对照组( P＜0.01);各试验组乳体细胞数与对照组相比均有所降低, MH、MM、HL、LH、LM组极显著低于对照组( P＜0.01) . 4)在氮总排泄量方面,各试验组均极显著低于对照组( P＜0.01) ,其中以MM组最低,降低幅度达11.00%. MM组粪氮、尿氮极显著低于对照组( P＜0.01) ,MM、MH、HL组氮表观消化率、氮沉积极显著高于对照组( P＜0.01) .综合各项试验指标,以25.0 g/( d·头) RPMet+30.0 g/( d·头) RPLys为最佳组合.
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