Abstract: The experiment was conducted to study the optimal supplementary feeding quantity of grazing beef cattle in spring in Inner Mongolia grassland.Seventy-five Simmental beef cattle with average weight of (281.19±17.15)kg were selected and divided into 5 groups (group A,B,C,D and E) with 15 replicates per group.Those cattle grazed optionally and supplemented with 0,0.8,1.7,2.5,3.4 kg/d concentrate,respectively,according to beef cattle weight of 0,0.3%,0.6%,0.9% and 1.2%.Pre-trial period was 15 d,the trial period was 60 d.The results showed that,with the increasing of concentrate supplementation,the daily gain of beef cattle was gradually significant increased (P < 0.05);Group D were 331.25%,130.00% and 38.00% higher than that of group A,B and C,respectively,the apparent digestibility of dry matter and crude protein were significantly higher than that of other groups (P < 0.05).The daily income of group D was 11.22 yuan and were 183.33%,102.53%,36.17%,20.52% significantly higher than that of group A,B,C and E (P < 0.05),the fattening income of group D was the highest.According to above results,the optimum adding levels was 2.5 kg/d in spring under the condition of grazing in Inner Mongolia.The higher daily gain and higher economic benefits could be obtained under the optimal supplementary feeding quantity.

Key words: grazing beef cattle; concentrate supplementary feeding quantity; spring; average daily gain