Get your answers in by Friday, before I post the answer and if you guess correctly you could be drawn for a (small) prize!
Buttercup is a slightly pudgy bay arab who is being conditioned for endurance. He's boarded at a public stable and often uses the public arena across the street, which is also the location of the local trail head.
He's going across the state line and needs a health certificate in order to do his first spring endurance endurance ride.
Buttercup's coat is shiny and in good condition with no ectoparasites. He pooped during the exam and has well formed poop with a good consistency.
He has a temperature of 103.2*F (elevated), heart rate of 36/min, respiration of 12/min.
Mentation: Quiet, alert, and responsive
Eyes clear, no nasal or ocular discharge.
As the vet, you explain to the client that you are concerned about the elevated temperature. She replies that because it is a hot day, he probably just overheated in the trailer on the way here.
She's upset that you won't issue the health certificate and as she loads Buttercup back into the trailer, he seems to have trouble navigating the step up with his hind legs and then once in the trailer, almost falls down.
What is your top differential diagnosis considering you are located in Illinois and it is February 2013?