Metro had months of rehab and medication. Special horse shoes helped for a time, but in 2012 X-rays revealed his knee joints were closing up. A vet said they would lock up within two years, at which point Ron and Wendy would have to put their horse down.
"I didn't just want to put him out to pasture and forget about him. I was thinking about how we could spend time together," Ron says.
He had noticed that his spirited horse liked to bob his head to get attention and pick things up in his mouth. A professional artist himself, Ron wondered if he could convince Metro to hold a paintbrush.

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http://www.bbc.co.uk/news/magazine-39628629#