In this study, we investigated the e¡ects of animalp lant protein ratio in extruded and expanded diets on nutrient digestibility, nitrogen and energy budgets of juvenile soft-shelled turtle (Pelodiscus sinensis). Four extruded and expanded feeds (diets 1^4) were formulated with di¡erent animal^plant protein ratios (diet 1, 1.50:1; diet 2, 2.95:1; diet 3, 4.92:1; diet 4, 7.29:1). The apparent digestibility coe⁄cients (ADCs) of dry matter and crude lipid for diet 1 were signi¢cantly lower than those for diets 2^4. There was no signi¢c-ant di¡erence in crude protein digestibility among diets 1^4. The ADC of carbohydrate was signi¢cantly increased with the increase in animal^plant protein.Although nitrogen intake rate, faecal nitrogen loss rate and excretory nitrogen loss rate of turtles fed diet 1 were signi¢cantly higher than those fed diets 2^4, nitrogen retention rate, net protein utilization and biological value of protein in these turtles were signi¢cantly lower than those fed diets 2^4. In addition, energy intake rate, excretory energy loss rate and heat production rate of turtles fed diet1were also signi¢cantly higher than those fed diets 2^4. Faecal energy loss was signi¢cantly reduced with the increase in the animal^plant protein ratio. The ADC of energy and assimilation e⁄ciency of energy signi¢c-antly increased with a higher animal^plant protein ratio. The growth e⁄ciency of energy in the group fed diet1was signi¢cantly lower than those in the groups fed diets 2^4. Together, our results suggest that the optimum animal^plant protein ratio in extruded and expanded diets is around 3:1.
The effects of protein restriction with subsequent re-alimentation on compensatory growth (CG) of juvenile soft-shelled turtles (Pelodiscus sinensis) were investigated. The turtles were fed five diets containing different crude protein content (T1: 29.24%, T2: 31.42%, T3: 34.19%, T4: 37.16%, C: 43.31%), while the energy content remained constant for 4 weeks (restriction period) and then re-fed a diet (43.31% crude protein) for 7 weeks (re-alimentation period). During the restriction period, feed conversion ratio (FCR) significantly increased in all protein-restricted groups (T1-T4) compared with the control group (C). At the end of the restriction period, body mass in groups T1 and T2 was significantly lower than that in the control group. During the re-alimentation phase, weekly body mass gain in group T1 was greater than that of the control from week 5 to week 10. FCR significantly decreased in group T1 compared with the control. No significant differences in final body mass between C and T1 groups were found at the end of the re-alimentation period. These results indicated that soft-shelled turtles receiving a diet in which protein was reduced from 43.31 to 29.24% (approximate 33% reduction) for 4 weeks achieved a 6 week complete CG response.
The effects of dietary supplementation of lutein on the growth, haematological profile and pigmentation in target tissues of the soft-shelled turtles were investigated. Five experimental diets were prepared with lutein levels at 1.16 (D1, control), 70.3 (D2), 132 (D3) and 239 (D4) mg kg À1 , and one more high inclusion level of 3410 mg kg À1 (D5) was included for tolerance test. Each diet was fed to 24 juvenile turtles for 8w. Specific growth rate (SGR) in D2, D3 and D4 was significantly higher than that of group D1 and D5. Skin yellowness (b*) and chroma (C*) of both carapace and plastron skin were all significantly increased with higher dietary lutein levels. Dietary lutein supplementation turned the H°values of skins into yellowness. The accumulation of lutein in skin and muscle also augmented significantly with increasing lutein levels and fit a logarithmic correlation with dietary lutein levels. There were almost no differences in haematological parameters of all turtles. Lutein is an efficient and safe colourant in diet of soft-shelled turtle. The optimal inclusion levels for the highest SGR and desired skin colour in carapace and plastron of soft-shelled turtle were 162, 142 and 143 mg kg À1 , respectively.
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