Effects Of Different Dietary Protein Levels On Growing Performance, Blood Biochemical Parameters And Immune Function Of Early-weaned Piglets

This single factorial designed experiment was conducted to establish the appropriate dietary protein levels for optimal growing performance and optimal immune function via studying the effect of different dietary protein levels on growing performance, blood biochemical parameters and immune function of early-weaned piglets. In this study, diets with five graded levels of crude protein were 14%, 17%, 20%, 23%, 26% respectively. The experiment was based on corn-soybean meal-wheat diet. The energy and amino acid pattern in five diets were kept the same, Dlys:DSAA:DThr:DTrp=100:57:62:18. Eighty 21±ld, 6.45±0.16kg DLY [Duroc× (Landrace × Yorkshire)] crossbred piglets were randomly allocated into five treatments, 4 replications per treatment, 4 piglets per replication, half male and half female. The whole experimental period lasted for 28 days.The experimental results were as follows:1, Average daily gain (ADG) and average daily feed intake (ADFI) and F/G changed with the elevated protein levels quadratically. The established protein requirement of piglets was not the same when using different evaluation index. The optimal protein level was 20.4% for highest ADG for the first two weeks, 20.1% for the latter two weeks and 20.2% for the whole period, the optimal protein level was 19.6% for highest ADFI for the first two weeks, 19.5% for the latter two weeks and 19.5% for the whole period. The optimal protein level was 21.9% for lowest F/G for the first two weeks, 21.2% for the latter two weeks and 21.4% for the whole period. The diarrhea incidence, diarrhea frequency and diarrhea index were the lowest in 20% protein diet. When dietary protein content exceeded 20%, the diarrhea incidence, diarrhea frequency and diarrhea index of piglets increased with the elevated dietary protein level, all the three diarrhea indexes in 26% diet were significantly higher than those in other groups (p<0.01) .2, Serum TP, ALB, ALB/GLO and the activity of GOT, GPT were affected by dietary protein levels. TP, ALB, ALB/GLO increased with the elevated protein levels firstly and then decreased with the highest values occurred in 23% protein diet group. Among all the groups, both the activities of GOT, GPT in CP 26% group were the highest. The GPT activity in 26% protein group was higher than that in 14%, 17%,20% and 23% group by 114.31%(p<0.01), 53.56%(p<0.05), 111.79%(p<0.01) and 137.97%(p<0.01) respectively. The GOT activity in 26% protein group was higher than that in 14%. 17%. 20% and 23% group by %.34%(p<0.01), 27.44%(p<0.05), 81.58%(p<0.01) and 60.46%(p<0.05). Hemoglobin and SUN concentration were not influenced by dietary protein levels (P>0.05).3, Dietary protein levels affected piglet cellular immune function while the humoral immune was not influenced by dietary protein levels(P>0.05). T- lymphocyte transformation rate(LTT) in 23% protein group was higher than that in 14%, 17%, 20% and 26% protein group by 9.25%(p<0.05), 5.66%(p<0.05, 5.64%(p<0.05) and 0.43%(p>0.05) respectively. Difference of LTT between 23% and 26% protein group and LTT between any two groups of 14%, 17% and 20% protein groups were not significant (P>0.05). The active rosette forming rate (Ea%)in 23% and 26% protein group were both higher than in any other group (P<0.05), while Ea% in 23% protein group was higher than in 26% protein group (P>0.05). Both the differences of IgG and hemolysin in any two groups were not significant.Based on the comprehensive consideration of the experimental results: The optimal dietary protein level for piglets weaned at d 21 was 20.2% for the four weeks post-weaning for best ADG and 21.4% for lowest F/G The optimal dietary protein level to guarantee best immune function was 23%, which was higher than that for best growing performance.