Glucose Homoeostasis and Regulation in Lactating Mink ( Mustela vison ): Effects of Dietary Protein,Fat and Carbohydrate Supply

The ability of lactating mink dams to control glucose homoeostasis, when fed diets containing different ratios of metabolizable energy (ME) from protein, fat and carbohydrates, was studied by measuring plasma concentrations of glucose, insulin, glucagon, urea and free fatty acids (FFA), in the fasted and absorptive state 4 weeks postpartum, in two consecutive years. A total of 36 yearling female mink, fitted with jugular vein catheters and raising litters of six or seven kits, was fed ad libitum lactation diets with different amounts of ME derived from protein, fat and carbohydrates (year 1:61:37:2, 46:37:17 and 31:37:32; year 2:61:38:1, 47:52:1 and 33:66:1). After 3 h fasting the dams were fed 210 kJ ME of the experimental diets. Blood samples were drawn 10 and 5 min before feeding and 30, 60, 90, 120, 150 and 180 min postprandially. The glucose concentration was increased 30 to 150 min postprandially in dams fed the carbohydrate-containing diets (46:37:17 and 31:37:32), whereas the glucose concentration showed no postprandial response in dams fed the carbohydrate-free diets (61:38:1, 47:52:1 and 33:66:1). Plasma insulin concentrations were increased 30 to 120 min postprandially in all dams, irrespective of dietary treatment. Plasma concentrations of glucagon were higher ( P <0.005) in dams fed the low-protein diets (31:37:32 and 33:66:1) than in dams fed the high-protein diets (61:37:2 and 61:38:1). Postprandially, the glucagon : insulin ratios decreased in dams fed the carbohydrate-containing diets, whereas the glucagon:insulin ratios tended to increase in dams fed the carbohydrate-free diets. Plasma concentrations of urea were significantly higher in dams fed the high-protein diets. Plasma concentrations of FFA, measured in the second experiment (year 2) only, showed increased concentrations postprandially, the responses being significant in dams fed the 33:66:1 and 61:38:1 diets. In conclusion, the mink is able to regulate the concentrations of blood constituents involved in maintaining glucose homoeostasis, and thereby to adapt to a wide range of dietary protein and carbohydrate supply.