I only use the stalls for reproduction. I like the horses and sims to interact on their own since I have an overloaded household on the 'horsey' family I play, out of three families on Dragon Valley. The family was originally for a challenge. That challenge was completed, after which time, an unusual wild horse appeared on their lot. The horse had yellow fairy wings. So I decided to have play the family again -- adopt the fairy horse, followed by the impulse to import mares from each of three WA worlds so that all three normal mares had fairy winged foals.
The goal for this family is to have all of the horses as top winners at the competitions and sell each of them at the end of their careers for max simoleons as possible. Then the family will just be extras, and I'll let them live out their lives.
Here's the UI in-game, while one of the sims competes at the equestrian center (it's a rug, not a barn).
https://i.imgur.com/InsK6uz.jpg
There are more horses now and an additional sim that lives in this family.
At the residence I placed several cavaletti on the ground for horses to alternate among them to train themselves by jumping over the cavaletti, and train themselves to race using a couple racing posts. When one had a wish for a water jump, I added it to the lot and then second bar jump. So while one horse is cued to do the larger jumps, another is running the cavaletti and still another is training for races. While each of the sim adults also take their horses to a jumping course to maximize the skills.
Horses training themselves -- The horses are queued and will automatically start the course and go round to do rounds until their queue is done or they have other needs. The adult sims in the family learned to ride (at the start) via the MultiTab but also trained the horses that they'd be riding in the competitions.
The competitions take place at the equestrian center (in my case, the rug) and generally have to win races many times before they complete all the challenges.
I put a pond, and watering trough on the lot. There are NO fences. For the horses to maximize their inter relationships, I give them full freewill and no walls to block their freedom to interact with each other which randomly also fulfill wishes that I lock for them.
Because of the number of horses... I put the following three lots close together.
* So the home is a huge lot (64x64) where the horses all run free and tend to be around the smallish house all the time. One stall, no barn -- the house has a basement where most human skilling takes place.
* The equestrian center is a small lot (with the equestrian center rug) with a few jumps, water trough, a small building with amenities and a showtime stage (so it doubles as a Private Venue for gigs and simport).
* A third essential lot is just a ranch type lot with a jumping course, so the horses also have to do rounds that include all jumps including the fire obstacles. I do not know if fire from the jump can kill a sim, so I give shower cans to all the adults that are training horses.
Foals retain the "untrained" trait until they are trainable adults. Foals want to be near their mom and are more independent if they have the 'brave' trait (a reward). If your world has lots of storms, sim horses sometimes seem terrified so they just need a sim to go 'calm' them. I've read others put the horses in stalls and have less trouble with bad weather but in my game, I just send a human sim out to the scared horse to calm it and bad moodlet is gone. Eventually they seem less scared during stores. (I got so tired of the rain and ineptitude of adjusting my tempest settings at the time, that I had rain turned off til I started a third family and turned rain on again with better settings.)
ATM that's all the tips I can think of now (I'm half asleep). Hope some of it is helpful. Good luck!
