Chestnut Tannins in Laying Hen Diets: Nutrient Digestibility and Indications Towards Altered Fat Metabolism

Despite their general reputation as antinutritional due to their protein-binding capacity, tannin compounds could be used in limited dosages in animal nutrition. Hydrolysable chestnut tannin extracts (CT) possess less protein-binding traits, strong antioxidant and antimicrobial properties impacting digestive physiology and intestinal health. This study aimed to investigate the effects of CT supplementation on nutrient digestion and lipid metabolism of laying hens. Two basal diets differing in nutrient matrix were formulated to test the hypothesis that CT effects are diet-dependent: a highly digestible corn-soybean meal-soy oil diet (C) and a less digestible wheat-rapeseed meal-palm oil diet (W). Each diet was supplemented with either 0 (T0) or 500 mg/kg CT (T500), resulting in four treatment groups of nine hens each (C-T0, C-T500, W-T0, W-T500). Addition of CT increased fat digestibility in the C diet but not in the W diet, while crude energy digestibility and metabolizable energy were reduced in CT-supplemented C diets. Protein digestibility remained unaffected by CT addition. Plasma non-esterified fatty acids (NEFA) and antioxidant capacity (ORAC) increased in the C-T500 group but decreased in W-T500 hens, indicating diet-dependency of the effect of CT. There was a trend towards lower total bile salt concentrations in CT-supplemented groups. The ratio of deconjugated to conjugated bile salts tended to decrease, and the ursodeoxycholic acid: chenodeoxycholic acid ratio (UDCA:CDCA) increased, suggesting microbial modulation. Acylcarnitine profiles indicate enhanced β-oxidation and mitochondrial fatty acid utilization. Hydrolysable tannins from chestnut wood exert diet-dependent effects on nutrient utilization and lipid metabolism in laying hens. When combined with a highly digestible, unsaturated fat source such as soy oil, CT enhances fat digestibility and β-oxidation. These findings suggest that CT could modulate bile acid metabolism and antioxidant capacity, and depending on the lipid source, determine the net physiological impact of tannin supplementation.