| This study was conducted to investigate the effects of dietary cysteamine(CS) level on growth performance, serum biochemical indices and the expression of growth axis related genes of minks. These objectives of this experiment are to determine the dosage of supplement and the way of addition of CS, and to provide the theory basis for rational use of CS in minks by analyzing the growth performance, nutrient digestibility, serum parameters, fur quality and relative genes expression.The experiment was designed with a double factorial experiment. With one hundred and twelve minks(male and female in half) aged about 12 weeks with a similar body weight, they were randomly divided into 7 groups with 8 replicates per group and 1 minks per replicate by sex. The minks in control group(groupⅠ) were fed the basal diet, and the minks in groups Ⅱ, and Ⅲ Ⅳwere continuously fed the experimental diets supplemented with 60, 90 and 120 mg/kg cysteamine respectively; and the other three groups were fed the same level as the above three groups but at intervals of week. The experimental period was 60(growing period) and 50(fur-growing period) days respectively. The results were as follows: 1. The results of male minks in growing period: The ADG and ADFI increased first and then decreased as the CS levels increased, with a highest value observed in group Ⅵ and the ways of discontinuous feeding was significantly higher than continuous feeding(P<0.05); The F/G of 60, 90 mg/kg group was significantly decreased(P<0.05); The DM, CP and EE digestibility were significantly increased(P<0.05), with a highest value observed in group Ⅵ and with a higher value observed in the interval groups compared with the continuous groups; The RN of group VI was significantly higher than that of group I, III and V(P<0.05); The dosage of supplement and the way of addition of CS had no interactive effect on the production performance of the minks(P>0.05). The CS had no significant effect on serum TP, GLO and CHO(P>0.05); The ALB of group IV, V, VI and VII was significantly higher than group I(P<0.01); The urea of the CS groups was significantly decreased(P<0.01); TG of group II, III, VI and VII was significantly lower than group I and IV(P<0.01); GLU of group VI was significantly increased(P<0.01); ALB of interval groups was significantly increased(P<0.05), and urea was significantly decreased(P<0.01); Serum indices of 90 mg/kg group were the best; The dosage of supplement and the way of addition of CS had interactive effect on ALB, urea, TG and GLU(P<0.05). Serum SS level of group IV, V, VI and VII was significantly lower than that group I; The level of GH, GHR, IGF-I, IGF-IR, T3 and T4 was significantly increased(P<0.05), and the group II, III, VI and VII were better; In interval groups, SS was significantly decreased(P<0.05), and GH and T4 were significantly increased(P<0.05); Serum hormone levels of 90 mg/kg group were the highest; The dosage of supplement and the way of addition of CS had interactive effect on the promoting growth hormones(P<0.05). 2. The results of female minks in growing period: In groupⅤ, the ADG was significantly increased than group Ⅰand Ⅳ(P<0.05), and the F/G was significantly decreased(P<0.01), with a higher value observed in the interval groups compared with the continuous groups(P<0.05); The DM output of group V, VI and VII was significantly lower than group I(P<0.01); The DM, CP and EE digestibility were significantly increased(P<0.05), and the DM digestibility of interval groups was significantly increased(P<0.01); The FN and UN of group V, VI and VII was significantly lower than that of group I(P<0.05), and the RN increased significantly(P<0.05), with a highest value observed in group Ⅴ; The RN of interval group was significantly higher(P<0.05); The dosage of supplement and the way of addition of CS had interactive effect on the EE digestibility(P<0.05). Serum TP and ALB of group V and VI were significantly higher than group I(P<0.05); The urea of group III, IV, V and VI was significantly lower than group I and II(P<0.01); The GLU of group II, III and V was significantly higher than group I and VII(P<0.05); The TP, TG and CHO of interval groups were significantly increased(P<0.05); The urea, CHO and GLU of 60 mg/kg group were greater than the other two groups; The dosage of supplement and the way of addition of CS had interactive effect on the urea and CHO(P<0.05). Serum SS of group IV, V, VI and VII was significantly lower than group I(P<0.01); The GH, IGF-I and T4 of group IV decreased significantly(P<0.05); The SS and T3 of interval groups decreased significantly(P<0.05), and the level of GH and T4 increased significantly(P<0.05); The IGF-I of 60 mg/kg group was significantly higher than that of 120 mg/kg group(P<0.01); the way of addition and the supplementation of CS had interactive effect on the serum SS, T3 and T4 levels(P<0.05). 3. The results of male minks in fur-growing period: The ADG of group V, VI and VII was significantly higher than that of groupⅠand IV(P<0.01), and the F/G decreased significantly(P<0.01), with a higher value observed in the interval groups compared with the continuous groups(P<0.01); The F/G of 90 mg/kg group was significantly lower than that of 120 mg/kg group(P<0.01); The fur quality of CS groups improved, with the skin, aciculums and villus length of group Ⅵand Ⅶgreater than group Ⅰ(P<0.05); The aciculum length of interval groups was significantly increased(P<0.01), and the 90 mg/kg group was significantly higher than that of the other two groups(P<0.05); The CP digestibility of CS groups was significantly higher than group I(P<0.01), and the FN decreased significantly(P<0.05); The RN of group VI was significantly higher than that of group I, II and IV(P<0.05); The RN, NPU, and PBV of interval groups were significantly increased(P<0.05); The different ways of addition and the supplementation of CS had interactive effect on ADG, F/G, aciculum and villus length(P<0.05). CS remarkably decreased serum urea and TG levels(P<0.05); The urea of interval groups decreased significantly(P<0.01), and the urea and TG of 90 mg/kg group was significantly lower than that 120 mg/kg group(P<0.05). CS remarkably improved the serum GH, GHR and IGF-I levels, with a highest value observed in group Ⅵ; The SS level of group II, III and VI was significantly lower than group I and IV(P<0.05), and the 90 mg/kg group was significantly lower than 120 mg/kg group(P<0.05); The different ways of addition and the supplementation of CS had interactive effect on the serum GH, SS, GHR and IGF-I levels(P<0.05). 4. The results of female minks in fur-growing period: There was no significant different in production performance(P>0.05); The DM digestibility of group VI was significantly higher than group I, II and IV(P<0.05); The CP digestibility of group III, VI and VII was significantly higher than group I(P<0.01); The EE digestibility of interval groups increased significantly(P<0.01); The DM digestibility of 90 mg/kg was significantly higher than the other two groups(P<0.05); The FN of group III and VI was significantly lower than group I(P<0.05), with the RN increased significantly(P<0.01);The RN, NPU, and PBV were significantly increased in interval groups(P<0.05), with the best of 90 mg/kg. The serum TP level of group VI was significantly higher than group I, II and IV(P<0.01); The TP and GLO of interval groups increased significantly(P<0.05). CS remarkably improved the serum IGF-I level of group VI; The IGF-IR of group IV decreased significantly(P<0.05); The T4 of group V, VI and VII was significantly higher than group I(P<0.01); The IGF-I and T4 of interval groups increased significantly(P<0.01); The IGF-I, IGF-IR and T4 of 60, 90 mg/kg groups were significantly higher than 120 mg/kg group(P<0.05); The different ways of addition and the supplementation of CS had interactive effect on the serum T4(P<0.05). 5. Expression of relative genes: The expression of IGF-I, IGF-IR and GHR increased significantly(P<0.05), with a highest value observed in group Ⅵ and the expression increased first and then decreased as the CS levels increased; The IGF-IR expression of male minks in interval groups was significantly higher than that of continuous groups(P<0.01); The different ways of addition and the supplementation of CS had no interactive effect on the genes expression(P>0.05).In conclusion, under the experimental condition, CS could decrease the SS level of minks and incresse the level of promoting growth hormones, as well as improving the production performance. Comprehensive each index, in growing period, the optimal supplemental way of CS was the 90 mg/kg for female minks and the 60 mg/kg for female minks at weekly intervals; In fur-growing period, the CS in diets for minks was appropriate to add with the level of 90 mg/kg at weekly intervals. |
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