Vampire bats rapidly fuel running with essential or nonessential amino acids from a blood meal

In most mammals, running is fueled by oxidization of endogenous carbohydrates and lipids while amino acids contribute little (<5-10%). Common vampire bats (Desmodus rotundus), however, specialize on a unique, protein-rich blood diet. Therefore, we hypothesized that a) vampire bats would rapidly begin utilizing dietary amino acids to support running metabolism, and b) that relative reliance on essential and non-essential amino acids would be similar. We fed bats cow’s blood enriched either with isotopically18 labeled glycine (non-essential amino acid) or leucine (essential amino acid). Bats were exercised at speeds of $10$, $20$, and $30$ $m \cdot min^{-1}$ on a respirometry treadmill, allowing us to assess metabolic rate (i.e., $O_2$ consumption and $CO_2$ production) and track the oxidation of labeled amino acids in exhaled $CO_2$. Vampire bats oxidized amino acids as their primary fuel as indicated by a respiratory exchange ratio (RER = ratio of $CO_2$ production to $O_2$ consumption rates) of approximately 0.8-0.9 at all speeds, with the labeled meal accounting for as much as 60% of oxidized fuels at peak usage. Similar oxidation rates indicated bats did not discriminate between essential and non-essential amino acid use. These findings reiterate how strongly metabolism can be shaped by a specialized diet.