Small Intestine Microvilli Status, Immune System and Broilers Chickens Performance in Response to Threonine Requirement

This study was conducted to determine different levels of threonine on intestinal microvilli morphology, humoral immunity, carcass content and performance in broiler chickens. A total of 272 day-old broiler chickens (Ross 308) with 4 treatments, 4 replicates and 17 birds in each were arranged in completely ran-dom design (CRD). Treatments were included 4 levels of starter, grower and finisher threonine in diets (0.96, 0.91, 0.86, 0.81); (0.87, 0.82, 0.77, 0.72); (0.78, 0.73, 0.68, 0.63%) respectively. At the end of the experiment, intestinal morphology, performance and blood parameters were measured. The results showed that the primary immune response against red blood cells was reduced (P<0.05) by decreased dietary threonine levels, in contrast, the amount of IgG and total antibody were increased with increasing levels of dietary threonine, (P<0.05). Increased threonine levels at 42 days of age resulted in higher lymphocyte counts and an elevated heterophil-to-lymphocyte ratio (P<0.05). Increased villus length, crypt depth, and villus length to crypt depth ratio were indicated by the high levels of threonine in the diet (P<0.05). The numbers and height of microvilli were reduced by decreasing threonine levels. In general, it can be con-cluded that increasing the level of threonine in the diet improved intestinal condition, which in turn could improve performance.