| This study focused on the effects of dietary copper levels and sources, copper and zinc interactions on the production performance in mink. Hopefully, this paper could provide a reliable bas is for the establishment of mink nutrition standard by determination of growth performance, nutrient utilization, serum biochemical indices, digestive tract enzyme activity, element accumulation and fur quality and systematic research of the digestion, absorption and metabolism of copper as well as the impact of copper on other nutrition.The paper consists of three parts:Part 1: Optimum copper levels in minkLate growing period test: One hundred and sixty 60-day-old healthy mink(80♂+80♀) were randomly assigned to 8 treatment groups with 20 animals in each group and fed a diet supplemented with either 0 mg/kg(Control group), 4 mg/kg(Cu4 group), 8 mg/kg(Cu8 group), 16 mg/kg(Cu16 group), 32 mg/kg(Cu32 group), 64 mg/kg(Cu64 group), 128 mg/kg(Cu128 group) or 256 mg/kg(Cu256 group) copper as Cu SO4?5H2O, respectively. The control diet contained 7.63 mg Cu/kg diet. The pre-test period lasted for 7 days, and trial lasted for 60 days. Our data showed that average daily gain increased(linear and quadratic, P<0.01) as Cu increased in the diet. Feed/Gain responded in a linear and quadratic fashion(♂: linear, quadratic, P<0.01; ♀: linear, P<0.05, quadratic, P<0.01)) with increasing level of Cu. Based on the estimated result of average daily gain by broken-line regression model, the copper requirement of late growing mink is 49.99(♂) and 49.54(♀) mg/kg, respectively. Apparent fat digestibility was increased by copper level(quadratic, P<0.01). Intake of copper, fecal copper, urinary copper, retention copper responded in a linear and quadratic(P<0.01) trend with increasing level of Cu. Nitrogen retention was increased by copper level(♂, quadratic, P<0.05; ♀, P<0.01). There was a linear and quadratic(P<0.01) effect of dose of Cu on plasma Cu concentrations. Serum TC(linear, quadratic, P<0.01), TG(linear, quadratic, P<0.01), CRE(quadratic, P<0.01) and Cu-Zn SOD(quadratic, P<0.01) was increased by copper level(quadratic, P<0.01). The initial body weight was greatly significantly and positively correlated with the final body weight(r=0. 9204, P<0.01). The average daily gain was greatly significantly and pos itively correlated with the fat digestibility(♂:r=0.8738, P<0.01;♀: r=0.8902, P<0.01). The retention copper(r=0.9228, P<0.01), plasma Cu concentrations(r=0.7046, P<0.01) was greatly significantly and positively correlated with copper level.Fur development period test: One hundred and forty 110-day-old healthy mink(70♂+70♀) were randomly assigned to 7 treatment groups with 20 animals in each group and fed a diet supplemented with either 0 mg/kg(Control group)、6 mg/kg(Cu6 group)、12 mg/kg(Cu12 group)、24 mg/kg(Cu24 group)、48 mg/kg(Cu48 group)、96 mg/kg(Cu96 group) or 192 mg/kg(Cu192 group) copper as Cu SO4?5H2O, respectively. The control diet contained 7.68 mg Cu/kg diet. The pre-test period lasted for 7 days, and trial lasted for 90 days. Our data showed that final body weight(linear, P<0.05; quadratic, P<0.01)and average daily gain(linear and quadratic, P<0.01) increased as Cu increased in the diet.V Feed/Gain responded in a quadratic fashion(P<0.01)) with increasing level of Cu; maximal Feed/Gain was seen in the Cu48 group. Based on the estimated result of average daily gain by broken-line regression model, the copper requirement of fur development period mink is 47.60(♂) and 38.88(♀) mg/kg, respectively. Supplemental dose of Cu linear ly increased( P <0.05) liver Cu and decreased(P <0.05) liver Fe level but did not alter(P >0.10) liver Zn. The spleen concentrations of Cu, Fe, or Zn show the same variations with the liver results. Supplemental dose of Cu linear ly increased( P <0.05) bile Cu and decreased(P <0.05) bile Mn and Fe level( linear, quadratic, P<0.01). Copper supplementation improved colour intens ity(linear, quadratic, P<0.01), overall fur quality(linear, P<0.05; quadratic, P<0.01). Colour intensity of those mink pelted suggested that relatively high levels of supplemental Cu have a benef icial effect on intensifying hair colour of dark mink. The retention copper(r=0.9569, P<0.01), plasma Cu concentrations(r=0.7243, P<0.01), liver Cu(r=0.8068, P<0.01), fur colour intensity(♂: r=0. 5286,P<0.01; ♀: r=0. 5409,P<0.01) was greatly significantly and positively correlated with copper level. The bile Fe concentrations was greatly signif icantly and negatively correlated with copper level(r=-0.9204, P<0.01).In conclusion, addition of the appropriate copper(Late growing period: 32 mg/kg; Fur development period:♂, 48 mg/kg ♀, 24 mg/kg) effectively improved grown performance. The data from this trial indicate that Cu plays an important role in the digestion of dietary fat in growing-furring mink. The data from this study indicate that improvements in growth performance are due to increased fat utilization and increased nitrogen retention. Based on the estimated result of average daily gain by broken-line regression model, the copper requirement of late growing mink is 49.99(♂) and 49.54(♀) mg/kg, respectively, and the copper requirement of late growing mink is 47.60(♂) and 38.88(♀) mg/kg, respectively. Colour intensity of those mink pelted suggested that relatively high levels of supplemental Cu have a benef icial effect on intensifying hair colour of dark mink. Copper supplementation improved overall fur quality.Part 2: Optimum copper sources in minkLate growing period test: The exper iment was conducted in a 3×3+1 factorial exper iment based on a completely randomized design. Two hundred and forty 24-day-old mink(120♂+120♀) were randomly distributed to ten treatment groups with 24 animals in each group. Animals in the control group were fed a basal diet(Cu 8.10 mg/kg). Mink in other nine treatments were fed basal diets supplemented with Cu from reagent-grade copper sulfate, tribasic copper chloride or copper methionate. Cu concentrations of experiment diets were 10, 25, and 40 mg/kg copper. The pre-test period lasted for 7 days, and trial lasted for 60 days. The apparent copper digestibility of 3 copper sources is copper methionine>tribasic copper chloride>copper sulfate. Bioavailability of Cu Met and TBCC relative to Cu sulfate was estimated from serum ceruloplasmin levels, and from serum Cu-Zn SOD activity using multiple linear regression and a slope ratio method. Compared with Cu SO4(100), relative bioavailability values of TBCC were 107.97 and 107.65%, based on serum ceruloplasmin and Cu-Zn SOD activity, respectively, and relative bioavailability values of Cu Met were 124.53 and 113.41%.Fur development period test: The experiment was conducted in a 3×3+1 factorial exper iment based on a completely randomized design. Two hundred and forty 24-week-old mink(120♂+120♀) were randomly distributed to ten treatment groups with 24 animals in each group. Animals in the control group were fed a basal diet(Cu 5.69 mg/kg). Mink in other nine treatments were fed basal diets supplemented with Cu from reagent-grade copper sulfate, tribasic copper chloride or copper methionate. Cu concentrations of experiment diets were 10, 25, and 40 mg/kg copper. The pre-test period lasted for 10 days, and trial lasted for 42 days. Bioavailability of Cu Met and TBCC relative to Cu sulfate w as estimated from serum ceruloplasmin levels, and from liver copper concentration us ing multiple linear regression and a slope ratio method. Compared with Cu SO4(100), relative bioavailability values of TBCC in male mink were 108.01% and 104.98%, and in female mink were 97.36% and 102.55%, based on serum ceruloplasmin and liver copper concentration, respectively, and relative bioavailability values of Cu Met in male mink were 116.48% and 110.97%,and in female mink were 104.98% and 110.10%.In conclusion, the relative bioavailability values of 3 copper sources is copper methionine>tribasic copper chloride>copper sulfate.Part 3: Influence of dietary zinc and copper on production performance in minkAn exper iment was conducted in a 3×3(Cu×Zn) factorial experiment based on a completely randomized design. One hundred and eight 8-week-old male mink were used as experimental animals. Prior to the study the mink were fed for 7 days adaptation period with gradual introduction of basal diet(without Cu and Zn supplementation). After 7 days adaptation per iod the mink were randomly distributed to nine treatments. Animals were fed basal diets supplemented with Cu from copper sulfate(Cu SO4) and Zn from zinc sulfate(Zn SO4). Supplemental Cu levels were 0, 15, and 30 mg/kg copper respectively, while supplemental Zn levels were 0, 150 and 300 mg/kg, respectively. Based on ADG, the optimal copper and zinc levels estimated by Box- Behnken were 51 and 117 mg/kg, respectively. Copper intake, excretion and retention was influenced by dietary copper(P=0.001), however, there was also a zinc-copper interaction on copper fecrs excretion(P=0.001) and retention(P=0.019). Zinc intake, excretion and retention was influenced by dietary zinc(P=0.001), there was no zinc-copper interaction. Moderate high Zn in the diet significantly reduced the apparent Cu digestibility, copper deposition in liver. In conclusion, the optimum dietary copper and zinc levels were 51 mg Cu/kg and 117 mg Zn/kg diet. |
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