In some situations, especially when doing intense performance activities, they need grain or a concentrate mix. They also need trace-mineralized salt and clean, fresh water. They need shelter from both cold and heat. You can provide them a clean, warm, comfortable place for resting with proper bedding materials. Routinely they need their hooves trimmed and may require shoes for certain performance activities.
Grooming is a daily task if they're stabled, and a necessity before and after riding.
And exercise is essential. Annually, have their teeth checked. They may need dental care. There are annual vaccinations against diseases and routine deworming for internal parasites between Sept. 1 and March 1. Horses need immunization for tetanus, Eastern and Western encephalomyelitis and influenza annually.