The effect of a mono-component exogenous protease and graded concentrations of ascorbic acid on the performance, nutrient digestibility and intestinal architecture of broiler chickens

A total of 640 male Ross 308 broilers were used in a growth performance and digestibility study to explore the interactive effects of a mono-component exogenous protease and ascorbic acid. A total of 7 dietary treatments were generated by formulation of a nutritionally-marginal wheat/soy-based 'negative control' diet and supplementation of the same with three concentrations of ascorbic acid, without or with exogenous protease addition. A further 'positive control' diet was fed as a reference and was formulated to be nutritionally adequate. Diets were fed ad libitum from d1-35 post-hatch and water and environmental controls were as per breeder recommendations. At the termination of the experiment ileal digesta was collected for assessment of digestibility and the ileum and jejunum were excised for morphological measurements. There were no interactions (P > 0.05) between ascorbic acid and exogenous protease for any of the measurements taken during the study. Overall (d1-35) addition of protease resulted in a significantly lower FCR compared with birds fed the negative control diet. There was no effect of ascorbic acid on performance of the birds with the exception of a small reduction in FCR at the highest inclusion concentration only. Ascorbic acid addition significantly increased gut integrity and exogenous protease reduced (P < 0.05) the presence of sialic acid in ileal digesta. Exogenous protease significantly increased the ileal digestibility of nitrogen and all amino acids but had no effect (P > 0.05) on dry matter digestibility. Ascorbic acid addition had only modest effects on ileal nutrient digestibility but this was confirmed as significant for several amino acids including threonine and cysteine. Finally, addition of ascorbic acid linearly decreased crypt depth in the jejunum and exogenous protease increased villus height, reduced epithelial thickness and goblet cell number in the jejunum. It can be concluded that ascorbic acid and exogenous protease improve intestinal integrity in growing broiler chickens and offer potential as a strategic dietary intervention to enhance performance, intestinal resilience and nutrient recovery.