Effects of Dietary Betaine on Growth Performance, Digestive Function, Carcass Traits, and Meat Quality in Indigenous Yellow-Feathered Broilers under Long-Term Heat Stress.

Simple Summary: Heat stress, one of the major problems in tropical and subtropical regions, adversely affects poultry production. This study was designed to evaluate the effects of dietary betaine on growth performance, digestive function, carcass traits, and meat quality in indigenous yellow-feathered broilers subjected to long-term heat stress. The results demonstrated that long-term heat exposure reduced the growth performance, digestive function, and carcass yield, and dietary betaine supplementation partially alleviated the adverse effects of heat stress on these parameters. These findings are useful for development of anti-heat stress feed additives in indigenous yellow-feathered broilers. Heat stress has a profound effect on poultry health and productivity. The present study evaluated whether feeding betaine could ameliorate long-term heat stress-induced impairment of productive performance in indigenous yellow-feathered broilers. A total of 240 five-week-old male broilers were randomly allocated to five treatments with six replicates of eight broilers each. The five treatments included a thermoneutral zone control group (TN, fed basal diet), a heat stress control group (HS, fed basal diet), and an HS control group supplemented 500, 1000, 2000 mg/kg betaine, respectively. The TN group was raised at 26 ± 1 °C during the whole study, HS groups exposed to 32 ± 1 °C for 8 h/day from 9:00 am to 17:00 pm. The results showed that heat stress decreased the body weight gain (BWG) and feed intake of broilers during 1–5, 6–10, and 1–10 weeks (p < 0.05). Dietary betaine tended to improve the BWG and feed intake of broilers under 5 weeks of heat stress (linear, p < 0.10), and betaine supplementation linearly increased the BWG and feed intake during 6–10 and 1–10 weeks (p < 0.05). Additionally, nitrogen retention was reduced by 5 weeks and 10 weeks of heat stress (p < 0.05), whereas dietary betaine could improve nitrogen retention in heat stressed broilers after both 5 and 10 weeks of heat stress (linear, p < 0.05). Moreover, this study observed that the trypsin activity of jejunum was decreased by 5 weeks of heat stress (p < 0.05), whereas betaine supplementation had quadratic effects on trypsin activity of jejunum in heat stressed broilers (p < 0.05). Furthermore, 10 weeks of heat stress induced a reduction of villus height of the duodenum and jejunum (p < 0.05), and decreased the villus height to crypt depth ratio of the jejunum (p < 0.05). Supplementation with betaine ameliorated the adverse effects of heat stress on these parameters (p < 0.05). Compared with the TN group, 10 weeks of heat stress reduced carcass and breast yield (p < 0.05) and betaine supplementation improved carcass and breast yield of heat stressed broilers (linear, p < 0.05). In conclusion, dietary supplementation of betaine could reduce the detrimental effects of long-term heat stress on growth performance, digestive function, and carcass traits in indigenous yellow-feathered broilers. [ABSTRACT FROM AUTHOR]