Hunger
A horse’s Hunger need is satisfied with either hay from a stall or hitching post, or from grazing on grassy ground. A hitching post object or a box stall object will provide a constant source of water and feed for your horse to enjoy.
Better though, is to buy Hay Bales or Hay Stacks, then run the Scatter interaction on the hay. Horses who eat fresh hay get the Extra Nutritious positive moodlet and even learn skills faster!
Sims with at least one level of Cooking skill can also make gourmet pet food for their horses. Horses love the granola treat. Feed them this regularly to keep them healthy and long-lived. Horses also love carrots, which is a new harvestable your Sims can grow. Buy some at the grocery store to feed to your horses as treats, or grow some in your garden. Feeding a horse a carrot gives it the MMM Carrots positive moodlet.
Mmm... carrots!
Bladder
Horses aren’t shy about it: When they gotta go, they go. You can’t really housebreak a horse and horses never go into bladder failure. Horses do have a ground-based Pee interaction, or can be directed to pee, but they will also take care of this function themselves without your intervention. And if you install a box stall object on your lot, you can collect the wonderful horse fertilizer for your garden.
Energy
Horses need their sleep. When their Energy need is low, horses will not want to exercise, and may throw their rider or break free if being led. Put your horse in his stall and let him get a good night’s sleep. The box stall’s Nap interaction lets the horse sleep until fully rested. Horses can nap anywhere, but they regain energy faster inside a stall.
Social
Horses need love and attention just like any pet. Horses can fulfill some of their Social need by grooming each other, or interacting with other pets, but to really fill their Social need, spend time with your horse. Riding, grooming, or talking to your horses keeps them from becoming lonely.
Exercise
Exercise is an important need for horses. Horses love to run, and they get quite cranky if they’re cooped up for too long. Keep your horse fit and happy with frequent, regular exercise.
Thirst
All that exercise will make your horse thirsty! Make sure you provide a source of clean fresh water for your horse. Horses can drink from just about any water source, from ponds and pools to the clean water in their stall or hitching post. Water troughs are a good option because they’re inexpensive and horses can play in them for Fun.