Balancing of protein and lipid intake by a mammalian carnivore, the mink, Mustela vison

Many herbivores and omnivores can balance their intake of macronutrients when faced with nutritionally variable environments. Carnivores, however, are widely believed to optimize their rates of prey capture and energy intake rather than balancing nutrients. We tested nutrient balancing in captive mink and found a pronounced ability to balance and regulate intake of protein and lipid. When faced with one of several different pairings of complementary foods varying in protein to lipid composition, mink apportioned intake between the two foods to defend a near constant ratio and amount (intake target) of the two macronutrients. When given only one food of fixed nutrient composition, mink balanced macronutrient intake relative to the intake target, without showing the excessive energy intake on diets with a low percentage of protein and energy deficit on diets with a high percentage of protein previously reported for herbivores and omnivores, including humans. This demonstration of nutrient balancing in a carnivorous mammal indicates that the capacity for nutrient balancing is a more general phenomenon across trophic levels than was hitherto believed to be the case. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.