I used to have a pony that foundered very easliy, I knew what to look for in her to get ontop of it quickly, but just wondering what everybody else looks for to get ontop of a foundering horse quickly.
A better idea than looking for signs of founder, is preventing ponies (and horses) from getting excessively fat in the first place. As soon as our ponies start getting cresty and fat deposits on either side of the spine, we restrict their grazing. The old saying 'prevention is better than cure' is just so true in the case of founder.
It's all very well to stop them getting fat, but I've seen horses of perfectly healthy weight founder to the point where they eventually needed to be put down overnight. It can hit quickly, and the horse does not always need to be fat.