Different preference is modulated by the feeding stimulants supplementation in different Chinese soft-shelled turtle (Pelodiscus sinensis ) basic diets

Five 2-week feeding trials were conducted to investigate five stimulants on P. sinensis. Two isonitrogenous and isoenergetic diets were formulated, one contained 600 g kg–1 fishmeal (FM diet) and the other contained 420 g kg–1 fishmeal and 225 g kg–1 animal protein blend (APB diet), and each tested one stimulant with four levels. The feeding stimulant candidates were betaine, 2-carboxy-ethyl dimethyl sulphonium bromide (DMPT), inosine-5′-monophosphate (IMP), taurine and squid extract. In the experiment on each stimulant, turtles (10.85 ± 0.10 g) were equally divided into FM and APB groups and fed with an equal mixture of corresponding diets containing four levels of stimulants, respectively. Each diet contained a unique rare earth oxide as inert marker. Turtles were fed twice daily (8:00 and 17:00), and faeces were collected. Preference for each diet was estimated based on the relative concentration of each marker in the faeces. In the FM group, only IMP showed the enhanced attraction. But in APB groups, all the stimulants, except IMP, showed higher preference than basal diets for at least one inclusion level, and the optimum level was 10 g kg–1 for betaine, 0.1 g kg–1 for DMPT, 0.1 g kg–1 for IMP, 5 g kg–1 for taurine and 10 g kg–1 for squid extract, and the squid extract had the strongest stimulating effect among the stimulants.