Box Elders and Seasonal Pasture Myopathy
Minimizing the risk of SPM
Clearly all horses in pastures where box elder trees are found do not get seasonal pasture myopathy. There are important risk factors to consider when decided what to do with pastures containing box elder trees.
1) Age; young horses are much more predisposed to SPM. Either they are more adventurous and likely to eat the seeds or possible older horses learn not to eat the seeds.
2) Previous exposure; some horses have lived their loves on pastures with box elder trees and never been ill. They may have learned not to eat the seeds or they may have a tolerance
3) Turn out for > 12 hours/day; if horses are on pastures with box elder trees for long periods especially if the pastures are grazed down they are more likely to eat seeds
4) Not having anything else to eat on fall pastures; In late fall the grass can look green and horses can look well fed but over grazed pastures may have little nutrient value and horses will start looking for something else to nibble on, including box elder seeds.
5) High numbers of seeds and high levels of toxin in seeds. The more box elder trees, the greater the risk horses will eat seeds. Toxin levels in seeds are highly variable from tree to tree and possibly year to year. The higher the toxin level the fewer seeds horses need to eat to become sick. Some years we see cases of SPM and some years we don’t.
What to do about turn out if you are concerned about SPM
1) Minimize your horse’s exposure to box elder seeds in the fall
• Don’t expose horses to pastures with box elder trees in the fall if;
• horses are young or new to this pasture, pastures are overgrazed, horses are turned out more than 12 h/day, horses do not get hay to eat on pastures
• If this is your situation either cut down the trees or avoid that pasture in the fall
• Conversely, if horses have been on the pasture for years in the fall, have lots of grass or hay to eat on the pastures then box elders on pastures may not need to be removed
2) Provide other things to chew on; Ensure you horse is fed before being turned out on fall pastures with box elders and has access to hay while on fall pastures
3) Reduce turn out time in October and November on these pastures if risks are present
4) Keep new horses and young horses off high-risk fall pastures