Effects of Dietary Protein Level on Growth Performance,Nutrient Digestion and Metabolism,and Serum Biochemical Indices of Blue Foxes during the Winter Hair Period

The experiment was conducted to study the effects of dietary protein level on growth performance,nutrient digestion and metabolism,and serum biochemical indices of blue foxes during the winter hair period.Ninety healthy male blue foxes with an average body weight of(5.71±0.60) kg were randomly assigned into 6 groups with 15 replicates per group and 1 blue fox per replicate.The blue foxes in the 6 groups were fed 6 experimental diets containing 24%(group Ⅰ),26%(group Ⅱ),28%(group Ⅲ),30%(group Ⅳ),32%(group Ⅴ) and 34%(group Ⅵ) protein,respectively.The experiment included an adaptation period for 7 days and a test period for 80 days.The results showed as follows: the highest final weight,average daily gain and feed conversation ratio were found in the group Ⅲ.Among them,the final weight in the group Ⅲ was significantly higher than that in groups Ⅰ,Ⅱ,Ⅴ and Ⅵ(P0.01),and the average daily gain and feed conversation ratio in the group Ⅲ were significantly higher than those in groups Ⅰ,Ⅴ and Ⅵ(P0.05 or P0.01).The dry matter digestibility in groups Ⅱ,Ⅲ and Ⅳ was significantly higher than that in groups Ⅰ,Ⅴ and Ⅵ(P0.01).With increasing protein level,protein digestibility was increased,but no significant differences were found among all groups(P0.05).The highest fat digestibility was found in the group with the diet containing 28% protein,and the significant differences were found between the group Ⅲ and other groups(P0.05).With increasing protein level,the fecal nitrogen output and urinary nitrogen output were increased,and urinary nitrogen output in groups Ⅴand Ⅵ was significantly higher than that in groups Ⅰ,Ⅱ,Ⅲ and Ⅳ(P0.01).The highest net protein utilization,biological value of protein and higher nitrogen retention were found in the group with the diet containing 28% protein.With increasing protein level,the serum urea nitrogen content was increased,while the contents of total protein and albumin in serum were firstly increased and then decreased,and the highest values were found in the group Ⅲ.The serum glutamic pyruvic transaminase activity was not influenced by different levels of protein(P0.05),and the serum glutamic oxalacetic transaminase activity in the group Ⅰ was significantly lower than that in other groups(P0.05).In conclusion,the appropriate dietary protein level for blue foxes during the winter hair period is 28% by combined with the parameters such as the average daily gain,nutrient digestibility,nitrogen metabolism and serum biochemical indices.