Does anyone know anything about phototoxicity or wild plants?

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Poor dhorse has what looks like the world's worst ever case of sunburn all over his nose and under his chin. It came up all of a sudden, almost overnight and he has never shown signs of sunburn before despite his white face, so I don't think it is 'just' sunburn iyswim. I googled photosensitivity and frightened myself silly reading about liver damage but the vet says we can rule that out, he is too young and shows no other symptoms.
He has been in the top part of the field so I went up there today and had a look at the plants and then came back and looked through my encyclopedia of herbs (yes, I do own one, I am that sad) and I'm pretty sure we have lovage. I've also found this list of plants that can cause skin redness and burns, if you scroll down lovage is listed.

Do you think I'm on the right track? Has anyone ever had a problem like this before? I can keep him off that part of the field but tbh it's practically the only grass we have left and the hay situation isn't good. If I have to I'll go and pull the plant up, there isn't that much of it but I already have a bad back so would like to avoid if poss!. I mean, even if that was the cause would it necessarily mean that he will always react to it or could it be a one-off? He has been in same field for 3 years with no problems. I could ring vet and ask I suppose but just wondered if there were any clever types on here first.

Dhorse is very miserable and stayed in his shelter today, he's had some bute for the pain. It was horrible, the vet had to give him two lots of sedation as it is impossible to touch his face at the best of times, then he picked off all the scabs and it was all bright red and bleeding but he said the air had to get to it (I got brownie points for commenting that it was just like mudfever). He's rubbed in some antibiotic cream and the udder cream that we'd already bought but couldn't get near enough to put on, so we've just got to give it a few days to settle down and see what happens.

Lovage has a strong smell of celery which would help you to identify it.
Buttercups can cause severe irritation to gums/lips and the digestive tract if the horse eats them fresh (harmless in hay). This is the most common cause of burn like symptoms in the muzzle area.
The classic cause of photosensitisation is St. John's Wort.

If the shortage of rain has caused very sparse grazing horses have been known to eat buttercups despite their acrid taste.

Thanks will have a sniff tomorrow! I read about St John's wort but I've googled it and I'm sure we haven't got any of that.

I may have got it wrong about it being a plant but it just seems so strange. We've had boiling temps here for weeks and he's been fine, now it's overcast and he has 'sunburn'.

Sounds very odd to me, is there any possibility that someone has dumped a nasty chemical in the field where he is? Fly tipping is rife around here and some of the waste dumped has been toxic.

Horses don't generally touch fresh buttercups unless they are very hungry indeed and after a quick google I can't find lovage listed as a plant that is poisonous to horses. St Johns wort sounds a possibility - it is quite tall and straggly with yellow flowers at this time of year.

I came back to ask about dumped chemicals - but see that Callisto has beaten me to it.

I agree that horses don't usually eat buttercups if there are other options - but have seen it cause similar problems to those described twice in as many decades...

With St. John's Wort, I would expect all white/unpigmented areas that get exposed to the sun to be affected, not just the muzzle area.

Giant hemlock would also cause burns in sunlight in areas exposed to the sap (by chewing for instance), but it is not common (and I think you might recognise a 6 foot rather chunky umbelliferate with off white flowers)and also, I have never heard of horses eating it.

Oops!, Giant hog week, not giant hemlock...
And it is a lot more commong than it was, especially in wet areas.

I give up
Giant hogweed.

Some pasture weeds, such as St Johns wort, and several fungal toxins that are found on legumous plants (clovers, alfafla) can cause photosensitivity and increase the sunburn risk.

Also, liver damage caused by toxins can cause rashes and photosensitivity on the skin.

Alsike Clover toxicity would be my main suspicion - several horses (all from the same field, natch) at the riding school DD goes to have suffered this summer.

"There's a thread on a horse forum here". It's in the US, but very informative about the tests and potential for liver damage.

Hi thanks for replies, suspect plant has now been chopped down with shears and removed from field so at least we can rule that out if the problem persists. Can't see any sign that anyone has dumped anything at all and I'm sure he's not hungry enough to eat the few buttercups that are there as there is some grass even in the most grazed area due to him being away for 5 weeks. Also he has a feed and hay twice a day.
Hopefully this is a one-off and the cause will remain a mystery. Poor little horse is still very miserable though and he's usually such a happy soul. Goodness knows how headshy he's going to be after all this.

All good replies. I'd also suggest that it may be just as a result of the new (and exciting!) wet weather. Our pink nosed ponies are worse today because their muzzles are wet from the grass and this has increased the power of the sun - hence they have brown scabs today.

Thanks Butkin but until last night it hadn't rained here for weeks.

(Though our impending camping holiday will no doubt cure that!)

He won't need to eat the buttercups to have a reaction. I am renting a field to a neighbour and her white faced chestnut had a terrible reaction to uncut buttercups - scabby and bleeding (which the horse had when she arrived), but as soon as the field was topped and most of the buttercups beheaded it has disappeared without a trace, leaving no scarring. She used Sudocrem on it by the way.

I'd never seen it before (and my grey pony doesn't get it), but she said her horse had it every year......

Hi, I thought I'd better let you know we've tracked down the culprit in case anyone else has it growing in their field. It's wild parsnip. The link is an american one but another site says it?s a "perennial found in mainly dry, chalky grassland, widespread and common in the South East of England." Guess where we live? Yup, the South Downs.

It must have been growing in the field in previous years for us to have so much of it, but we've never had a problem before and so never noticed it. Dhorse has been in the field for 3 years and before that my appaloosa was in there for several years without a mark on him despite being pink all over. The only thing I can think of is that we usually rest the top of the field (it is a long strip going up the side of a hill) from early spring and then gradually strip-graze our way up throughout the summer. The horses don't usually get up to the very top until the autumn, but which time this plant has died back. This year, due to the difficulty of getting the electric fence canes in the hard ground we have changed the routine and instead of moving the fence a little bit each day we've just let the horses up the top for a few hours and then brought them back down again at night. Needless to say it will be business as usual next year!

Anyway, hopefully poor dhorse will recover now (plus my sister's pony who started showing symptoms this week) and we will have to speak to the farmer who owns the field to see if he has any suggestions for how to get rid of the horrid stuff for good.

Oh it also spends one or two years in rosette stage and then blooms in favourable conditions, which may be another reason why we haven't noticed it up until now, as we do usually take notice of what is growing in our field! It must be the fact that we've actually got a hot summer for once that has brought it out.

I use Tim Couzens, the holistic vet, for my horses. I sent him a photo of my pony, whose nose was looking rather as you describe. Tim said it was an allergy, sent some white pills, and within a week it was all clearing up nicely. Just in case anyone has something similar, I find holistic vets really handy for all sorts of things.

My welsh a gets this a lot. So did the stud where I used to work. As butkin says, is due to sun and dew. It also can appear on her heels, and does look a lot like mud fever, but occurs when the fields are bone dry. Liberal applications of sudocreme on nose and feet clear it up in a few days.
We have had an old show pony who ate something ( oak) and became photosensitive. It mainly affected his white socks, which became swollen, covered in clear yellowish crusts and oozed when scabs were broken. he also had sudocreme applied, hibiscrub works well too.

Oh I'm a great fan of sudocreme, use it for everything including sunburn normally. However this wasn't a case of slapping it on and being better in a few days. There's a pic on my profile of dpony's nose (he was like this under his chin and round his heels as well). It's taken weeks of treatment (with burns cream from vet) rather than days to get better, plus my mum still has scars on her arms because she touched some of the wild parsnip before we knew what it was and came up in blisters.

I'm used to dealing with the odd bit of sunburn but I hope I never see our poor horses suffering like this again. They haven't known what to do with themselves.

Anyway, evil weed has now been mown down by the farmer and he's going to spray it for us as well. Thank goodness!

Jesus Christ almighty! Just looked at the picture! Poor baby! Is he ok now?

He is fine thanks, they all are, (neighbours included, they were all affected at the same time) almost back to their normal selves. They still flinch if something goes near their faces but the skin is lovely and pink, not even a scar, amazing really.