With the recent "rescue craze" that I'm seeing take over social media, I thought I'd do a little piece on something I see done improperly so often with rescue horses - rehabilitating their digestive system.
Often, new rescue owners see a starved horse and think "oh! He needs food!" They begin to immediately feed the horse all the hay he could want, and start him on a supplemented grain regiment. The problem is, this is a recipe for killing a horse. Even starting on unlimited hay can lead to a condition called Re-feeding Syndrome. Re-feeding Syndrome occurs when a horse is suddenly introduced to a large amount of carbohydrates, which causes an insulin release. This insulin release pulls electrolytes out of circulation - electrolytes a starved horse is already low on. This results in red blood cell collapse, which causes respiratory, cardiac and kidney failure, and subsequently death. This typically occurs within 3-5 days of reintroduction to food.
Luckily, there are steps you can take to avoid this and safely re-introduce food to a starved horse. For the horse's first 3 days, he should only be fed 1lb (~1/6 flake) leafy alfalfa hay every 4 hours. Then from days 4-10, the horse should be given hay in slowly increasing amounts, until they are eating 4lbs of hay every 8 hours. After day ten, the horse may be transitioned to as much hay as they can eat in two feelings per day. Neither grain nor supplements should be added until several months into re-feeding, to prevent a sudden boost in metabolism that could kill the horse.
I hope this was helpful, and feel free to ask any questions you have below!