When I lived in OR and worked a couple different barns all the horses got North West Supplement. It was pelleted feed formulated for horses living in the NorthWest because of the selenium deficiency up there. Don't know if they make it anymore, this was in the early 90s.
I also calved heifers up there and we gave the calves a Vit. E/Selenium shot as soon as they hit the ground. Selenium deficiency in calves causes growth ******ation, muscle atrophy, inability to gain and even collapse and death.
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.