Vampire bats rapidly fuel running with essential or non-essential amino acids from a blood meal.

In most mammals, running is fuelled 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 (i) vampire bats would rapidly begin utilizing dietary amino acids to support running metabolism, and (ii) that relative reliance on essential and non-essential amino acids would be similar. We fed bats cow's blood enriched either with isotopically labelled glycine (non-essential amino acid) or leucine (essential amino acid). Bats were exercised at speeds of 10, 20 and 30 m min^-1 on a respirometry treadmill, allowing us to assess metabolic rate (i.e. O₂ consumption and CO₂ production) and track the oxidation of labelled amino acids in exhaled CO₂. Vampire bats oxidized amino acids as their primary fuel as indicated by a respiratory exchange ratio (RER = ratio of CO₂ production to O₂ consumption rates) of approximately 0.8-0.9 at all speeds, with the labelled 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.