This subject is interesting because at first glance you would think that this shouldn't be a big deal if it helps them breath but apparently if it is taken too often it could have serious side effects. I'm not into harness racing but don't they run once a week?
http://www.drugs.com/mtm/oxymetazoline-nasal.html
Excerpt:
What is the most important information I should know about oxymetazoline nasal?
Do not use oxymetazoline nasal for longer than 3 to 5 days. Longer use could cause damage to your nasal tissue and lead to chronic congestion.
