Growth and fur characteristics of blue foxes (Alopex lagopus) fed diets with different protein levels and with or without DL-methionine supplementation in the growing-furring period

A production trial was carried out on 125 growing-furring blue foxes (Alopex lagopus) to study the effects of low-protein diets, with or without DL-methionine supplementation, on growth performance and fur characteristics. The treatment codes were P30, P22.5, P22.5M, P15, and P15M. The protein contents [g kg^-1 DM (dry matter)] of the diets were 300, 243, 243, 174, and 177, respectively. DL-methionine was added to P22.5M and P15M to yield a total dietary content of methionine (M) corresponding to that in P30. From August to mid-September, the weight gain of the blue foxes receiving the diet with the lowest protein level and the lowest methionine content (P15) was significantly lower than that of the blue foxes in treatments P22.5 and P30. In contrast, growth of the blue foxes in P15M did not differ from that of the blue foxes in P22.5 or P22.5M. From midSeptember to pelting, weight gain did not differ significantly among treatments. Guard hair quality was significantly impaired in the low-protein diets without methionine supplementation, but not in those diets supplemented with methionine. Methionine appeared to be the first limiting amino acid for winter fur development. Addition of DL-methionine and use of low-protein diets for blue foxes would be beneficial in terms of reduced feed expenses and lower nitrogen emissions to the environment.