To be deductible, business expenses must be ordinary and necessary. "An ordinary expense is one that is common and accepted in your field of business. A necessary expense is one that is helpful and appropriate for your business. An expense does not have to be indispensable to be considered necessary."
What is the business reason for these expenses? If you are advertising for new clients, then it would be advertising. If you are providing ordinary care for your horses, then the gear they wear is probably just a regular upkeep expense, and the advertising expense would be anything you paid for a professional photographer, or to boost the post on social medial. (If you are just showing off on social media and have no real business purpose, then maybe it's not even a deductible business expense.)
