Effects Of Dietary Vitamin C On Immunity, Antistress And Proximate Compositions Of Chinese Soft-shelled Turtle

Vitamin C is an essential micronutrient for aquatic animals. Chinese soft-shelled turtle was used as target animal in this research. Effects of vitamin C on immune indices, serum complement, immunoglobulins levels and enzyme activity, antistress and meat quality parameters such as body proximate compositions and contents of collagen in muscle, liver, carapace and calipash were studied.Sixty Chinese soft-shelled turtles (average weight 150g) were randomly divided into five groups, each included four replicates of 3 soft-shelled turtles. Experimental diets supplemented with five levels of 0, 100, 200, 400, 2000mg per kg diet vitamin C in the form of L-ascorbyl-2-polyphoshate were respectively fed to turtles twice a day. After 60 days of feeding, all turtles were decollated to collect spleen, muscle, carapace, calipash and blood samples for analysis.The results showed that supplementation of dietary vitamin C in soft-shelled turtle could elevate levels of complements (C₃ and C₄) and immunoglobulins in plasma. In contrast to the control, addition of 2000mg/kg vitamin C could raise the content of complement C₃ by 286.67% (P<0.05) and excelled the other treatment groups (P<0.05); supplementation of 200mg/kg vitamin C could increase the content of complement C₄ by 33.33% (P<0.05). A concentration of 200mg/kg, 400mg/kg and 2000mg/kg could improve the levels of IgM by 40.62% (P<0.05), 43.30% (P<0.05) and 90.48% (P<0.05) compared with the control. While dierary supplied with 400mg/kg and 2000mg/kg could elevate the content of IgA by 9.39%(P<0.05) and 12.73% (P<0.05) compared with the control. No significant changes were found in the content of IgG (P>0.05).The activity of lysozyme (LSZ), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) increased with increasing dietary vitamin C levels, and dietary supplied with 2000mg/kg showed enhanced enzyme activity by 68.75% (P<0.05), 7.93% (P<0.05), 43.23% (P<0.05), 94.45% (P<0.05) and 222.41% (P<0.05) respectively compared with the control. Also, vitamin C supplementation exerted significant effects on the activity of acids phosphates (ACP), alkaline phosphatase (ALP) and myeloperoxidase (MPO), they respectively peaked in the groups fed at 400mg/kg vitamin C, 400mg/kg vitamin C and 200mg/kg vitamin C by 29.74%, 66.76% and 76.89% respectively compared with control.Dietary vitamin C could improve the antistress ability of Chinese soft-shelled turtle. Serum glucose (Glu) and cortisol in turtle decreased with dietary vitamin C addtion. In contrast to the control, the treatment groups with 100mg/kg, 200mg/kg, 400mg/kg and 2000mg/kg respectively decreased by 35.17% (P<0.05), 31.98% (P<0.05), 34.59% (P<0.05) and37.89% (P<0.05).Essential amino acids (EAA), non-essential amino acids (NEAA), total amino acids (TAA) and fresh flavor amino acids (FAA) levels of muscle and calipash increased with increasing dietary vitamin C levels. Also polyunsaturated fatty acids (PUFA) increased with increasing of dietary vitamin C levels, while saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) decreased. And a concentration of 2000mg/kg vitamin C could improved the contents of TAA, EAA, NEAA, FAA in muscle by 4.61% (P<0.05), 4.49% (P<0.05),4.42% (P<0.05) and 3.75% (P<0.05) compared with the control. At the same time, research showed that 2000mg/kg vitamin C could elevate the contents of TAA, EAA, NEAA, FAA in calipash by 3.75% (P<0.05), 1.66% (P<0.05), 2.63% (P<0.05) and 1.31% (P<0.05) compared with the control. In contrast to control, dietary supplement of 2000mg/kg vitamin C could enhance the levels of C18:2, C18:3, C20:4, C22:6, C20:5, C22:5 by 17.33%,33.33%,16.54%,17.29%,13.07% and 25.16% respectively. Lactate dehydrogenase (LDH) and creatine kinase (CK) activity in muscle of Chinese soft-shelled turtle decreased with increasing dietary vitamin C, the dietary with 2000mg/kg vitamin C significantly decreased by 36.28% and 37.29% compared with control (P<0.05). At the same vitamin C concentration, the levels of malefic dialdehyde (MDA), cholesterol (CHO)and creatinine (CRE) of muscle were notably less than those of control (P<0.05). However, supplementation of vitamin C showed no significant differences on proximate compositions in muscle and calipesh.Dietary vitamin C supplementation also influenced contents of collagen in muscle, liver, carapace and calipash of Chinese soft-shelled turtle. The levels of collagen of muscle, liver, carapace and calipash raised with increasing dietary vitamin C levels and peaked in the same group fed at 400mg/kg diet.