Optimum Copper Levels And Sources In Growing And Furringblue Foxes

Blue fox is a valuable fur-bearing animal. In recent years, blue foxe rearing is expanding unceasingly. China has become the largest blue fox rearing country throughout the world. With the developing of the blue fox farming, nutrient studies in blue foxes were also carried out quickly. Copper(Cu) is an essential trace element for blue foxes because of its vital roles in the progress of growth and fur development. To date, the study about Cu nutrition in blue foxes is still blank. This study was conducted to investigate the effects of Cu levels, Cu sources and Cu-Zn interaction in growing and furring blue foxes. There are four sections in this study.Section one: Optimum dietary copper level in blue foxesGrowth period: 100 blue foxes at the age of 55 days were randomly assigned into 5 groups with 20 replicates(10 males and 10 females) per group and 1 fox per replicate. The foxes in the 5 groups were fed experimental diets which contained 7.89(control), 20(Cu20)、40(Cu40)、80(Cu80)、160(Cu160) mg/kg DM respectively. The pre-test period lasted 7 days and the trial period lasted for 60 days. The results showed as follows: ADG and FCR were greater in Cu 40 compared with control group(P<0.05). Using the nonlinear model predicted the optimum Cu levels in growing period were 46.73mg/kg for males and 53.41 for females. The digestibility of DM, Cp and EE were greater in Cu 40 than those in control group(P<0.05). Cu intake, Cu excretion and Cu retention was increased with the increasing of dietary Cu levels(P<0.01). The maintain Cu requirements in growing blue foxes in 0.47 mg/d/kg LW. Serum Cu in Cu160 was higher than control group(P<0.05). The activity of Cp in Cu160 was greater compared with control group(P<0.05).Fur development period: The experiment design was similar to growth period. The results showed that foxes in Cu40 and Cu80 had higher ADG and FCR than control groups(P<0.05). Using the nonlinear model predicted the optimum Cu levels in furring period were 61.41mg/kg for males and 61.97 mg/kg for females.The digestibility of EE in Cu40 and Cu80 were greater than control group(P<0.05). N retention in control was lower than that in Cu40 and Cu80(P<0.05). The maintain Cu requirement is 0.34 mg/d /kg LW. The concentration serum TP, ALB and Cu were higher in Cu160 than that in control group(P<0.05). Cu supplementation decreased the concentration of CHO and incresaed HDL-C(P<0.05). Liver Cu content greatly increased with the increasing of dietary Cu levels(P<0.01). The activities of Cp and GSH-Px were higher in Cu160 than control(P<0.05). Guard hair and underfur length were higher in Cu40 an Cu160 than Cu20 and Cu80(P<0.05). Fur color in Cu160 was darker than that in control group(P<0.05).Section two Optimum copper source in blue foxesGrowth period: A 2 ? 3 factorial experimental design was conducted to investigate copper sources(copper sulfate and copper methionine) and supplemental levels(0, 50 and 100 mg Cu/kg DM) on growth performance, nutrient digestibility and relative bioavailability of copper methionine compared to copper sulfate.The results showed that: Cu supplementation improved ADG and FCR in both copper sources(P<0.05).There were no significant differences in growth performance between Cu S and Cu M(P>0.05). Cu addition improved the digestibility of DM, CP and EE(P<0.05). Cu output was significantly increased by Cu addition(P<0.01). Under same supplemental level, foxes fed Cu M excreted less copper than foxes fed Cu S(P<0.05). The activity of Cp was increased with the increasing of dietary Cu levels(P<0.05). The relative bioavailability of Cu from Cu M to Cu S was 127.91%.Fur development period: A 2 ? 4 factorial experimental design was used to investigate copper sources(copper sulfate and copper methionine) and supplemental levels(0, 50, 100 and 150 mg Cu/kg DM) on growth performance, nutrient digestibility and relative bioavailability of copper methionine compared to copper sulfate.The results showed that: Cu addition increased the ADG and decreased the F:G(P<0.05). Cu supplementation improved the digestibility of DM and EE(P<0.05). Cu output was significantly increased with high Cu addition(P<0.01).Under same supplemental level, foxes fed Cu M excert less copper than foxes fed Cu S(P<0.05). Liver Cu was increased with Cu addition(P<0.01). Foxes fed Cu M had higher liver Cu than those fed Cu S(P<0.05). With the increasing of Cu addition, hair Cu was significantly increased(P<0.01). The relative bioavailability of Cu from Cu M to Cu S was 111.63%. Cu supplementation up-regulated the expression of GHR and IGF-1(P<0.01).Section three Optimum copper and zinc level in blue foxesGrowth period: A 2 ? 3 + 1 factorial experimental design was conducted to investigate dietary copper(30, 45 and 60 mg/kg) and zinc(40 and 120 mg/kg) addition on growth performance, nutrient digesitibility and serum biological paramenters in blue foxes. The result showed that: Diet supplemented with 30 mg/kg Cu /40 mg/kg Zn and 45 mg/kg Cu and 60 mg/kg Zn had higher ADG than control group(P<0.05). Cu supplementation increased the digesitibility of CP and EE(P<0.05). With the increasing of dietary Cu levels, Cu excretion was greatly increased(P<0.01). High Zn addition increased Cu excretion(P<0.05).Fur development period: A 2 ? 4 factorial experimental design was conducted to investigate dietary copper(0, 20, 40 and 60 mg/kg) and zinc(40 and 200 mg/kg) addition on growth performance, nutrient digesitibility and fur quality. The results showed that:Cu supplementation increased ADG and decreased F:G(P<0.05). Both Cu and Zn addition improved the digestibility of EE(P<0.05). With the increasing of dietary Cu level, Cu excretion increased significantly(P<0.01). High Zn addition increased the Cu excretion(P<0.05). Liver Cu was increased by Cu addition(P<0.05). Both Cu and Zn addition increased the activity of Cu-Zn SOD and GSH-Px(P<0.05). Cu addition tended to darken fur color(P=0.07).In conclusion, the suitable Cu level in growing blue fox is 40 mg/kg DM and the relative bioavailability of Cu from Cu M to Cu S was 127.91%. The suitable Cu level in furring blue fox is 40 ~ 80 mg/kg and the relative bioavailability of Cu from Cu M to Cu S is 111.63%. Cu supplementation can up-regulate the expression of GHR and IGF-1. Moreover, dieraty Cu addition can improve antioxidant status and darken fur color.