Abstract: Abstract: 【Objective】Effects of protein levels on growth, nutriments digestion and absorption ,and blood biochemical indexes of calves were examined.【Method】Nine new born calves with same conditions were selected and divided into 3 groups, named as A, B, C group, fed three kinds of milk replacers which had different protein levels (18%,22%,26%) respectively. Five periods digestion metabolism trials were taken on 12～20days, 22～30 days, 32～40 days, 42～50 days and 52～60days after birth of the calves .【Result】The results showed that the growth curves of all groups in 11-61 days were similar, but the growth rate of 22% group was higher than 18% and 26% groups 8.89%,19.48％ respectively. As age increased, the apparent digestibility of DM declined gradually and apparent digestibility of EE rose a little, while apparent digestibility and retention of N showed increasing trend. Compared with 22%, 26% groups, calves in 18% group had a poor performance on DM, EE and N apparent digestibility. The average apparent digestibilities of N in three groups were 69.39%, 75.36% and 74.55% respectively. Both apparent digestibility and retention of Ca, P went steadily throughout the whole trials, but the average apparent digestibility of P in 26% group was only 63.83% and lower markedly than 18% group ( 70.40%) and 22% group ( 69.73%). TP,ALB,GLO contents in calves blood of 22% group were greater than 18%, 26% groups. Serum Urea content in 18% group calves was lower significantly. Glu concentration in 22% group was 5.38mmol/L and was greater than 18％ group’s 3.71mmol/L and 26％ group’s 4.09mmol/L when the trials finished.【Conclusion】Protein Levels of milk replacer and different biology phases had influence on nutrition’s digestion metabolism and blood iochemical indexes of Calves. Calves fed cp22% milk replacer had a better performance than other groups on growth.

Key words: calves, protein levels, milk replacer, apparent digestibility, retention