This aim of the present study was to evaluate the effects of dietary xylooligosaccharides (XOS) on the intestinal morphology, nitrogen metabolism, faecal ammonia release, antioxidant capacity, and immune organ indices of broilers fed corn-soybean meal diet. A total of 240 healthy 1-day-old Arbour Acres (AA) broilers were randomly divided into four treatment groups receiving XOS supplementation of 0 (Control), 150, 300, and 450 mg/kg to basal diet for 6 weeks. Six replicates with 10 birds each were prepared for each treatment. Results showed that the villus height of duodenum, jejunum, and ileum and the villus height to crypt depth ratio of jejunum were increased significantly in the broilers receiving 150 mg/kg XOS compared with those in the Control (p < 0.05). Nitrogen utilisation from day 19 to 21 was higher in the 150 mg/kg XOS group than in the Control (p < 0.05). Moreover, the addition of 150 mg/kg XOS reduced the nitrogen excretion from day 40 to 42 (p < 0.05), and all XOS treatments increased the nitrogen utilisation from day 40 to 42 (p < 0.05). All dietary XOS supplementations decreased the faecal ammonia concentration on day 21 (p < 0.05), and the addition of 150 and 450 mg/kg XOS induced a lower faecal ammonia concentration compared with that of the Control on day 42 (p < 0.05). Dietary supplementation of 300 and 450 mg/kg XOS enhanced the activity of serum total antioxidant capacity compared with that in the Control and 150 mg/kg XOS groups at the age of 42 days (p < 0.05). Supplementation with 450 mg/kg XOS significantly increased the index of thymus (p < 0.05) and the content of total protein compared with those of the Control at the age of 21 days (p < 0.05). Therefore, dietary supplementation with 150 mg/kg XOS have a beneficial effect on broilers.

A total of 240 1-day-old Arbor Acres broiler chickens were randomly distributed to 4 treatment groups with 6 replicates and 10 birds per replicate. Chickens were fed with corn-soybean meal diet supplementation with additions of 0, 150, 300, and 450 mg/kg XOS for 42 days. At 4 weeks of age, the average feeding time was reduced in the 450 mg/kg XOS group (p < 0.05), and the percentage of feeding time was increased in the 300 mg/kg XOS group (p < 0.05). At 5 weeks of age, broilers fed with 300 mg/kg XOS had increased the percentage of feeding time (p < 0.05), and 450 mg/kg XOS had increased the feeding frequency and percentage of feeding time (p < 0.05). At 6 weeks of age, the feeding frequency was highest in the 450 mg/kg XOS group (p < 0.05). During 4 to 6 weeks of age, the average feeding time was increased in 300 mg/kg XOS group (p < 0.05), the frequency was improved in the 450 mg/kg XOS group (p < 0.05), and the percentage of feeding time was longer in the XOS group than that in the control group (p < 0.05). The average daily gain was improved during days 22–42 and days 1–42 in the 150 mg/kg XOS group (p < 0.05). Broilers fed with 300 mg/kg XOS had an increased eviscerated rate (p < 0.05). The pH_45min of breast muscle was highest in the 450 mg/kg XOS group (p < 0.05), as well as the pH_45min and pH_24h of thigh muscle, which improved in the 300 mg/kg and 450 mg/kg XOS groups (p < 0.05). In addition, the cooking loss of thigh muscle was reduced in the 300 mg/kg XOS group (p < 0.05). In conclusion, dietary supplementation with XOS had positive effects on the feeding behavior, growth performance, and meat quality of broiler chickens.

N-carbamylglutamate (NCG) is a structural analog of N-acetylglutamate and has multifunctional roles in animal production. However, few studies have been conducted to evaluate the effects of NCG on protein digestive function and muscle growth in broiler chickens. This study investigated whether NCG could improve muscle growth via protein digestive ability and amino acid metabolism in broiler chickens. A total of 144 one-day-old male broiler chickens were randomly allocated to four treatments with six replicates of 6 broiler chickens each. The treatments were a basal diet and a basal diet with NCG supplementation at three graded levels (150 g/t, 300 g/t, and 450 g/t of NCG). The results showed that NCG supplementation significantly improved the average daily weight gain (ADG) and decreased the feed conversion ratio (FCR) compared to the control group (p < 0.05) and increased the weight of leg muscle and breast muscle. Furthermore, NCG supplementation significantly increased protein digestibility, the activities of amylase, trypsin and lipase, and villus height in the ileum (p < 0.05), which demonstrated that digestibility and absorption were improved by NCG in broiler chickens. Analysis of plasma amino acids, hormone levels and the gene expression of breast muscle revealed that NCG increased the concentration of GABA, glutamate, glutamine, leucine, threonine, valine, branched-chain amino acids and essential amino acids and the levels of testosterone and IGF-1 in plasma (p < 0.05). Additionally, NCG increased the expression of mTOR and P70S6K in breast muscle tissue. Therefore, NCG supplementation could be an important nutritional strategy to improve product performance, muscle growth and development, and meat yield. The 300 g/t supplementation level was found to be the practical optimum dose, as it produced effects comparable to the highest dose (450 g/t) on most parameters while offering better cost-effectiveness. This study provides new insights into the application of NCG for meat production improvement in broiler chickens.