Growth performance, jejunum morphology and mucin-2 gene expression of broiler Japanese quails fed low-protein diets supplemented with threonine

The present experiment was conducted to examine the effects of threonine supplementation in low-protein diets on growth performance, jejunum morphology, and mucin-2 gene expression in meat-type Japanese quails. A total of 800 broiler quails were assigned to 8 dietary treatments based on a factorial arrangement (2 × 4) across 1-35-day period. Experimental treatments consisted diets with 180 g/kg (CP180), 200 g/kg (CP200), 220 g/kg (CP220), and 240 g/kg (CP240) crude protein content each supplemented with 100% and 110% threonine requirement of broiler quails. Growth performance of broiler quails was not affected by interaction of dietary protein and threonine contents while daily weight gain was higher in birds received CP240 than those given CP180 and CP200 (p < .05). Carcase yield increased in response to consumption of diets with 200 g/kg protein content and 110% threonine requirement compared to those receiving the other dietary treatments (p < .05) except for birds in CP240 group. Villus height to crypt depth ratio was higher in birds subjected to CP200 and CP240 each supplemented with 100% and 110% threonine requirement of quails, respectively, than the other groups (p < .05). Digestibility of protein was not affected by experimental treatments. Expression of mucin-2 gene decreased by dietary supplementing graded levels of protein (p < .05) while increased by graded levels of threonine (p < .05). In conclusion, reduction of dietary protein content did not affect the growth of broiler quails whenever diets added with 100% of their digestible threonine requirement. Furthermore, dietary protein content below 220 g/kg adversely affected DWG of quails.Highlights Reduction of dietary CP content did not affect the growth of broiler quails whenever diets added with 100% of their threonine requirement. Morphology of the small intestine was influenced by variations in dietary energy and protein contents. Expression of mucin-2 gene decreased when quails fed on diets with graded levels of CP while increased with graded levels of threonine.