The impacts of dietary protein on growth, body proximate composition, feed utilization, amino acid profile, digestive enzyme activity and amino acid metabolizing enzymes in soft‐shelled turtles (Pelodiscus sinensis) (initial weight: 4.02 ± 0.06 g) were measured during an 8‐week feeding trail. Six diets containing 8%, 18%, 28%, 38%, 48% and 60% (control group) fishmeal were formulated, which contained 14.38%, 20.41%, 26.19%, 32.23%, 37.63% and 45.23% protein respectively. Weight gain, mean feed intake, skirt ratio, pepsin activity of stomach, total amino acid of the muscle and crude protein levels of the whole body improved as dietary protein content increased from 14.38% to 26.19% but remained stable thereafter. The hepatosomatic index, feed conversion ratio, intestinal alpha‐amylase activity, moisture content of the whole body and serum alanine transaminase and aspartate aminotransferase activity decreased with increasing protein content up to 26.19% and then plateaued. The protein productive value and protein efficiency ratio decreased as protein content increased. Intestinal lipase activity and crude lipid levels of the whole body were unaffected by dietary protein level. Hepatic alanine transaminase and aspartate aminotransferase activity first significantly increased with increasing protein but remained stable at protein content ≥26.19%. The optimum dietary protein level for soft‐shelled turtles was in the range of 27.36%–28.46% based on weight gain, ALT activity and AST activity results.
we conducted an 8-week feeding trial to determine the effects of dietary starch levels on growth performance, body composition, and digestive enzyme activities of juvenile soft-shelled turtles. six fish meal-based diets containing 120, 180, 240, 300, 360 and 420 g kg −1 cornstarch were formulated. body weight gain (bwg), crude protein concentration in whole body, as well as protease activity increased with increasing dietary starch levels until the highest at 240-300 g kg −1 , but it was decreased at higher dietary starch content. In contrast, the feed conversion ratio, moisture content and hepatosomatic index were the lowest at 240-300 g kg −1 of cornstarch. the weight gain correlated significantly with the survival rate, the crude protein composition and the protease activity, but correlated negatively to the moisture content and the hepatosomatic index. the optimal dietary starch levels for the maximum BWG and maximum protease activity were 267.25 g kg −1 and 266.79 g kg −1 , respectively. The α-amylase activity was the lowest at 120 g · kg −1 of cornstarch, and increased with increasing cornstrach content. the lipase activity and the amount of crude lipid in the turtles were not influenced by dietary cornstarch. Our results suggest that around 300 g kg −1 of cornstarch in diets is optimal for juvenile soft-shelled turtles.
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