I can't recall seeing anything on treatment on the battlefield.

Have you seen Trumpet of Glory. The Military Career of John Shipp, first veterinary surgeon to join the British Army by Ernest A. Gray (London, Robert Hale, 1985) ?

And at a different level there is a chapter in Andrew Bamford's Sickness, Suffering and the Sword. The British Regiment on Campaign, 1808-1815 on beasts of burden that should be useful.

There is some good information in regimental histories and Wellington's correspondence about the effect of illness and hardship on the strength of cavalry regiments - for example Fane's brigade of heavy cavalry arrived in Lisbon in late April 1809. It saw no active service over the next two months, but on 27 June 1809 Wellington told Castlereagh that it would have to leave almost 100 horses behind when it advanced due to the effects of climate and change of feed (Wellington Dispatches (1844) vol 3 p 329-30 - see also Moyle Sherer Recollections p 70 for a good description of their shabby appearance.