Effects Of Low Protein Diets On Production Performance, Immune Function And Metabolism Of Nutrients In Broilers

The present experiment was conducted to study the effects of dietary crude protein levels ( 21%, 19.5% and 18% in the earlier three weeks; 19%, 17.5% and 16% in the later three weeks, respectively) on production performance, immune functions, blood indexes, and metabolism of nutrients in broilers. In the experiment, single-factor test design was adopted, and a total of 180 1-day-old healthy male Arbor Acre broilers were selected and randomly allotted into three treatments, each treatment consisted of six replicates with ten broilers in each replicate. The feeding trial lasted 42 days, and experimental diets and water were available ad libitum during the entire experimental period. The experimental results were showed as follows:(1) When the dietary crude protein level was 1.5 percentage points lower than the common level, the growth performance of broilers maintained the same level as the control group, but the slaughter performance improved modestly. However, when the protein level was 3 percentage points lower than the common level, the growth performance of broilers decreased significantly (P<0.05).(2) When the dietary crude protein level was 1.5 percentage points lower than the common level, immune organ indexes and the cellular immune level didn't change significantly compared with the control (P>0.05), and humoral immune level improved. And when the protein level was 3 percentage points lower than the common level, immunoglobulin levels increased, but Newcastle disease antibody was significantly lower than the control group at 21 day of age (P<0.01), and the other immune indexes had no obvious difference compared with the control group.(3) When dietary crude protein level decreased by 1.5 percentage points, broilers increased the deposition of nutrients to some extent, improved protein synthetic metabolism; but when the dietary crude protein level decreased by 3 percentage points, utilization of nutrients for broilers was lower than the control group (P<0.05).(4) While reducing the level of dietary crude protein by 1.5 percentage points, compared with the control group, the levels of total protein, albumin, globulin in serum showed no significant difference (P>0.05), but the serum urea nitrogen decreased significantly (P<0.01) on day 21; when the dietary crude protein level decreased by 3 percentage points, the levels of total protein, albumin, globulin in serum were lower than the control group (P<0.05).(5) When the dietary crude protein level decreased by 1.5 percentage points, villus height, villus width and crypt depth in small intestine of broilers showed no significant difference compared with the control group (P>0.05), at the same time, there was no significant difference in cecum microflora among treatments; while the dietary crude protein level reduced by 3 percentage points, the villus height decreased, and villus width increased, and crypt depth increased too, but cecum microflora showed no significant difference compared with the control group (P<0.05).