Addition of phytase to a high plant protein-low phosphorus diet increases growth and nutrient absorption and alleviates intestinal damage in bullfrogs (Lithobates catesbeianus)

Abstract

This experiment was conducted to investigate the effects of adding phytase to a high plant protein diet on growth performance, digestion, absorption and intestinal health in bullfrogs (Lithobates catesbeianus). Six experimental diets were prepared with normal phosphorus (NP), low phosphorus-high plant protein (LP0), and then 750, 1500, 2250 and 3000 phytase units (FTU)/kg phytase were added to the LP0 diet, named LP750, LP1500, LP2250 and LP3000, respectively. Bullfrogs (33.21 ± 0.12 g) were fed each of the six diets for 56 days. Bullfrogs fed the LP2250 and LP3000 diets showed higher weight gain rate than bullfrogs fed the LP0 diet. Bullfrogs fed the LP1500, LP2250 and LP3000 diets showed higher lysozyme activity and lower diamine oxidase activity in the serum than bullfrogs fed the LP0 diet. Apparent digestibility of P in bullfrogs fed the LP2250 and LP3000 diets was higher than that of bullfrogs fed the LP0, LP750, and LP1500 diets, with no significant difference from bullfrogs fed the NP diet. Protein efficiency ratio of bullfrogs fed the LP1500, LP2250, and LP3000 diets was higher, and trypsin activity of bullfrogs fed the LP2250 and LP3000 diets was higher than that of bullfrogs fed the LP0 diet. Compared to the LP0 group, the expression of interleukin-1β and tumour necrosis factor α genes was significantly decreased, and the expression of interleukin-10, occludin and zonula occludens-1 genes was significantly increased in bullfrogs fed the LP750, LP1500, LP2250 and LP3000 diets. Compared to bullfrogs fed the LP and NP diets, bullfrogs fed the LP3000 diet had an increased abundance of beneficial bacteria Firmicutes and Bacillus in the intestine. In summary, the addition of 2250–3000 FTU/kg phytase to a high plant protein diet improved growth and nutrient absorption, and alleviated intestinal inflammation and damage in bullfrogs.