Effects of dietary level of crude protein and supplementation of protease on performance and gut morphology of broiler chickens

Protease supplementation in feeds can enhance the performance and gut morphology of animals. However, knowledge of the mechanisms by which protease leads to this improvement is limited. We investigated the influence of dietary level of crude protein (CP) and exogenous protease. A total of 800 male broilers (Ross 308, 1 day old) were randomly allotted to five dietary treatments containing 10 replicate pens with 16 birds per pen. The treatments included a standard diet (STD), STD with 0.75% lower protein without protease (S75), STD with 0.75% lower protein and protease (SP75), STD with 1.0% lower protein without protease (S100), STD with 1.0% lower protein and protease (SP100). The overall result showed a greater body weight gain (BWG) in the SP75 diet when compared with S75, SP100, and S100. Feed conversion ratio was lower in the SP75 diets compared with all other treatments. Digestibility of dry matter was highest in the SP75 diet compared with other treatments. Digestibility of CP in the SP75 diet was higher than that with S100. Increased digestibility of lysine was noticed in the protease supplemeted diets when compared with those without protease. Tryptophan, cysteine, and proline were higher in the SP75 diets compared with S100. Glutamic acid was higher in all the treatments compared with STD. The villus height (VH) and VH/crypt depth (CD) in the duodenum and jejunum were greater in the group receiving diets supplemented with protease when compared with those receiving diets without protease. On the other side CD was lower in the SP75 diet-group compared with S100. Similar result was obtained for CD in the ilium. But VH/CD in the ilium was higher in the SP75-, S75-, S100-, and the STD-diet group compared with S100. In conclusion, protease supplemented diets at the SP75-dose gave the optimum result in BWG and dry matter. Digestibility of CP, lysine, tryptophan, cysteine, glutamine, proline, and gut health such as the villus height and VH/CD in the duodenum, villus height, and VH/CD in the jejunum were also greater in the protease supplemented treatments.