Abstract: This experiment was conducted to investigate the effect of rumen-protected amino acid on production performance,milk composition,blood biochemical parameter and economic benefits in early lactation dairy cows. 96 healthy Holstein cows in the early lactation period were selected, the average days in milk was (65±15) d.The experimentation was designed in single factor random block design and according to age,parity and milk yield similar,the 96 dairy cows were randomly divided into control group and experimental group,with 48 cows in each group.The control group was fed with basal diet and the experimental group was fed with basal diet supplemented with rumen-protected methionine (RPMet):18 g/head·d,rumen-protected lysine (RPLys) 35 g/head·d.The results showed as follows:Compared with the control group,dietary supplementation of RPMet and RPLys increased daily milk yield (P=0.034) and had no effect on dry matter intake and feed conversion rate (P>0.050);The dietary supplementation of RPMet and RPLys decreased milk urea nitrogen (P=0.015),tended to increase milk fat percentage (P=0.096),and had no effect on milk protein,somatic cell count,milk lactose rate and total solids content (P>0.050); The dietary supplementation of RPMet and RPLys increased TP,ALB and GLU content (P<0.050),decreased BUN content (P=0.049),and had no effect on ALT,AST,GLOB,ALP,TG and TC content (P>0.050).The dietary supplementation of RPMet and RPLys increased economic benefits by 3.60 yuan/(head·d).In conclusion, dietary supplementation of rumen-protected amino acid increased the milk production and economic benefits in early lactation dairy cows.

Key words: dairy cows, rumen-protected methionine, rumen-protected lysine, production performance, milk composition