Lipid and amino acid composition influence incorporation and discrimination of 13C and 15N in mink

The incorporation of dietary macronutrients and associated isotopic signatures of carbon (delta C-13) and nitrogen (delta N-15) into animal tissues is a result of the interaction between growth, nutritional status, and the composition of the diet. In mammalian carnivores incorporation is further complicated by lack of carbohydrates in the diet and allocation of large quantities of dietary macronutrients to fetuses and milk production. In this study, we explored the effects of diet composition, growth, pregnancy, and milk production on isotopic incorporation of C-13 and N-15 in captive mink (Neovison vison) fed 3 experimental diets (Beef, Fish, and a Mixture of the 2) that differed in lipid and amino acid composition. In nursing kits, growth was the main factor influencing isotopic incorporation rates into muscle. Similarly, in adults, changes in body mass influenced the dynamics of isotopic incorporation in red blood cells, although the rates differed for delta C-13 and delta N-15, as well as among the 3 experimental groups. Effects of allocation of dietary macronutrients to fetuses and milk did not differ from body mass changes, potentially because those macronutrients were assimilated in tissues other than blood cells. Although incorporation of delta C-13 followed the expected exponential form, delta N-15 incorporation lagged in the Beef and Mixture diet treatments, and both delta C-13 and delta N-15 incorporation rates differed substantially for the Fish-fed mink. These differences in isotopic incorporation can be attributed to the differential oxidation of dietary amino and fatty acids. Thus, we advocate the development of compound-specific isotopic analyses to estimate dietary contributions through the incorporation of essential dietary fatty and amino acids.