Mysterious ailment that has its roots in the grass

In the years that followed, I learned a lot about this painful and difficult foot condition. It was so mysterious, coming apparently from nowhere when a horse had eaten too much, or just been out at grass, even winter grass. It could strike after an operation, or foaling, or a bout of colic, or as a result of working on hard ground, and sometimes after worming or steroids prescribed for something else.

My old pony spent a lot of time having her feet hosed with cold water, and the farrier was my constant friend. I knew him so well he gave me his secret Yorkshire pudding recipe, used to this day. It's brilliant.

But now we know something about laminitis, or "founder" as it once was called.

A horse's foot is essentially a box with a leg on the top and a fleshy frog on the bottom. Inside the box is a bone, the pedal bone, held in place by the laminae, and it is these membranes that cause all the trouble. Once upset – not inflamed – they come unstuck. Pressure builds in the inflexible hoof and the pedal bone starts to lose its proper place, dipping down at the front and in extreme cases, sinking to the bottom of the hoof. A sinker will often have to be put down.

The received wisdom is that it is a disease of fat ponies, fed too much corn or allowed to eat too much rich grass. But why? And why some and not others? Australian research tells us it's all about fructan in the gut.

Fructan is a carbohydrate found in grass. Some grasses produce more than others, with the old-fashioned varieties like timothy and meadow fescue producing much less than perennial ryegrass, the staple cattle grass of today. Temperature rises mean grasses produce more, which is why spring grass is dangerous, but sunlight can also stimulate production.

Horses digest sugars well but are less good with carbohydrates, so fructans tootle through a horse's gut more or less undigested. When they reach the hind gut though, they react with bacteria and break down, producing acid and the substances that cause laminitis.

All the other causes of laminitis are linked to this. Upsets to the system produce toxins within the gut which break down the structure of the laminae. But what can we do about it?

"Keep fat ponies off grass!" say the textbooks. Well, yes. But there's a welfare issue here. In all conscience I could not keep my little mare locked up all her life and I had to feed her something. "Bran and carrots," my friend Pam used to mutter. "The only foods no-one's rude about."

You can't miss a horse with laminitis; back feet tucked under the belly, front feet stretched out and an expression of total misery. Call the vet at once. Do not do as I did, and hose with cold water. The problem isn't too much blood, it's too little, and cold reduces the circulation still more. The vet will prescribe painkillers and acepromazine, while you should make the softest bed you can find.

Tom Pears, a remedial farrier from Penistone, advises complete rest. "In the acute phase, bones are moving," he says. "Keep that horse still."

You're going to see a lot of your farrier. Inside the foot is a pedal bone on a tilt, and he is going to trim the hoof to make it level again. If you can't get him then apply a bandage that spreads pressure to the frog. Some people recommend a pad of old carpet, others rolls of gauze, distributing the load across the foot. Just wrap it up somehow. When the farrier comes you are going to ask him to put on a heart bar shoe.

With luck, it will all calm down. Watch, though. Tissue may have died within that foot and an abscess could be forming. If nothing's happened in a month you're more or less safe.

Ever after though, you must be careful. Soak all hay, twice. Give a yeast supplement, to help the bugs in the gut. Fit a muzzle to your pony, even though he'll get it off in half a day. Or you can do what I did, and get some sheep. They take grass down to the nub, eating out ragwort and worms as they go.

My elderly pony lived very happily on what was essentially a bowling green and if no-one wanted a ride I walked her with the dog. Would I buy her again? Certainly. There's no accounting for love.