Effect of feed restriction with betaine and ascorbic acid supplementation on caecal bacteria, short chain fatty acid, blood biomarker, duodenal morphology and growth performance of meat ducks under heat stress

Under heat stress (HS) feed restriction (FR) can maintain blood biomarker homeostasis and improve poultry production. The objective of this study was to determine the effects of feed restriction with betaine and ascorbic acid supplementation on the digestive system and growth performance of meat ducks under HS. A total of 400 meat ducks were assigned to the following four groups: NC (normal temperature control group, 24 degrees C, feeding ad libitum), T1 (HSC, heat stress control group 34 degrees C, feeding ad libitum), T2 (HSFR, with 800 mg/kg dietary betaine supplementation and feed restriction), and T3 (HSFR, with 800 mg/kg dietary betaine and 300 mg/kg ascorbic acid supplementation in drinking water and feed restriction). FR was performed in the morning (05: 00-10: 00 h) and afternoon (17: 00-24: 00 h). Body weight and feed intake were lower in T1 and T2 groups than in the NC and T3 groups. The T1 group reached the lowest values. Blood pH values were higher and concentrations of blood biomarkers were lower (p<0.05) in the T1 group compared with the other groups, which did not differ significantly from each other. Villus height (VH), crypt depth (CD), and VH/CD ratio in the duodenum were significantly lower in the T1 group than in the other groups. Caecal Lactobacillus counts (p<0.05), but not coliform bacteria, bacteroids, or E. coli counts, were lower in the T1 group than those in any other group. Total short chain fatty acid (SCFA), acetic acid, and propionic acid contents were lower (p<0.05) in the T1 group than those in the other groups, which show high values in the following order NC > T3 > T2. In conclusion, under heat stress FR with betaine (800 mg/kg) and ascorbic acid (300 mg/kg) in the diet or water improved growth performance, blood parameters, caecal SCFA and microflora in meat-type ducks.