The rugged Icelandic ponies are not used to being indoors
Farmers in southern Iceland have been racing to protect their animals from being poisoned by volcanic dust.
The animals are at risk of fluoride poisoning if they inhale or ingest the ash, leading to internal bleeding, long-term bone damage and teeth loss.
Sheep, cattle and horses were rushed to shelter after they got lost in a fog of ash in areas near an erupting volcano.
Areas south of the Eyjafjallajoekull volcano have been caked in a layer of grey ash some 10cm (four inches) thick.
Ponds have turned into pools of cement-like mud and geese have had trouble flying because their wings are heavy with ash, media reports say.
On Sunday, farmers banded together to drive around searching for hundreds of shaggy Icelandic horses, who panicked and got lost in a downpour of ash that turned day into night.
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"The risk is of fluoride poisoning if they breathe or eat too much," Berglind Hilmarsdottir, a dairy farmer from Nupur, told the AP news agency through a protective white dust mask.
The fluoride in the ash creates acid in the animals' stomachs, corroding the intestines and causing haemorrhages.
It also binds with calcium in the blood stream and after heavy exposure over a period of days makes bones frail, even causing teeth to crumble.
"The best we can do is put them in the barn, block all the windows, and bring them clean food and water as long as the earth is contaminated," Ms Hilmarsdottir said.
Berglind Hilmarsdottir protects herself as she searches for her cattle
Sveinn Steinarsson, of Iceland's Horse Breeding Association, warned that Iceland's famously resilient ponies would be in danger if the ash contamination continued.
"In areas where there's ash fall and horses are outside, the conditions are terrible," Mr Steinarsson told the French news agency, AFP.
"They can't survive in this if it carries on too long. The horses have to be fed with hay and have access to running water to avoid them consuming a lot of ash."
Conditions on the ground immediately downstream of the volcano remained extremely difficult on Monday, said the BBC's Lorna Gordon in Iceland, and visibility was down to just a few metres.
Teams from the country's civil defence department have been visiting the farmers to offer support and advice using specially modified vehicles and armoured personnel carriers, our correspondent said.