Effect of dietary β-glucan supplementation on growth performance, carcass characteristics and gut morphology in broiler chicks fed diets containing different theronine levels

Abstract

The present study was conducted to investigate the effect of dietary β-glucan supplementation on performance, carcass characteristics and jejunal morphology in broiler chicks fed diets containing different threonine (Thr) levels. A total of 360 one-day-old Ross 308 broiler chicks were randomly distributed among 4 pen replicates of 6 dietary treatments according to a 2×3 factorial arrangement of treatments, including 2 different basal diets (control or diet supplemented with 30g/kg of β-glucan) and 3 different Thr levels (90, 100 or 110% of Ross recommendations during different growth periods). Trial lasted for 42days. In addition to performance parameters, 4 randomly-selected birds from each pen were slaughtered at the last trail day to evaluate carcass traits and morphological indices of jejunal epithelium. Results showed that dietary inclusion of β-glucan decreased (P<0.01) average daily feed intake (ADFI) during the starter and grower periods; consequently, it resulted in the significant decreases in average daily gains (ADG) during the starter (P<0.05), grower and entire (P<0.001) trial periods. In addition, feed conversion ratio (FCR) was increased (P<0.05) as a result of dietary β-glucan supplementation. Although ADFI was not affected by dietary Thr level, increasing Thr level increased (P<0.001) ADG, and in turn, caused the significant (P<0.01) improvements in FCR values during the starter, grower and entire trial periods. Dietary supplementation of 30g/kg of β-glucan increased (P<0.001) the relative weights of gizzard and small intestine. On the other hand, abdominal fat pad was decreased by supplemental β-glucan. Increase in dietary Thr up to 100% of recommended values resulted in an increase (P<0.01) in thigh percentage. Although dietary β-glucan inclusion decreased (P<0.001) villi height (VH), VH to crypt depth ratio (VH:CD) and villi absorptive surface area, it resulted in the significant (P<0.01) increases in submucosal and muscular layers thickness, and increased goblet cells count. On the other hand, dietary supplementation of Thr at the level of 110% of recommendations increased (P<0.01) VH:CD. The present findings indicated that dietary supplementation of β-glucan at high level diminished growth performance and impaired morphological indices of jejunal epithelial cells. On the other hand, Thr fortification of diet could compensate for a large part of these detrimental impacts on weight gain of broiler chicks.