Effects of dietary zinc levels on growth,serum zinc,haematological parameters and tissue trace elements of soft‐shelled turtles,Pelodiscus sinensis

A 10‐week feeding trial was conducted to evaluate the effects of dietary zinc (Zn) contents on the growth, tissue trace element contents and serum Zn levels in soft‐shelled turtles, Pelodiscus sinensis. Juvenile soft‐shelled turtles approximately 4.8 g in body weight were fed casein‐based diets containing seven levels of Zn (14, 23, 32, 43, 58, 87 and 100 mg kg^?1) for 10 weeks. There were no significant differences (P > 0.05) in weight gain (WG), feed conversion ratio (FCR) or protein efficiency ratio (PER) among the dietary treatments. However, Zn concentrations in the liver, serum and carapace of turtles fed the basal diet containing 14 mg Zn kg^?1 were the lowest among all groups. Zn contents in the liver, serum and carapace increased when dietary Zn increased up to a dietary Zn level of approximately 43 mg kg^?1. Beyond this dietary level, tissue Zn contents were relatively constant. Carapace iron (Fe), selenium (Se) in hard tissues and haemoglobin concentrations decreased when dietary Zn increased. Dietary Zn requirements of juvenile soft‐shelled turtles derived from regression modelling using the liver, serum, carapace and bone Zn contents as indicators were 42, 39, 35 and 46 mg Zn kg^?1, respectively.