How to understand horse emotions? Help pls.

If the horse is sad or won't play with the ball to have fun take use the "take horse for a ride option" and go for the one that sounds fastest. I always want to say extreme but that isn't the word they use. I was confused also when the horse was sad and didn't want to play. I felt making him practice or anything else would make it worse but on the second day of this behavior I decided it couldn't hurt to train and go for a ride. I was very please because he wasn't sad anymore. Taking him once a day keeps him happy.

@iheartsandwiches I'm navigating this myself just with horses purchased from the exchange. Bless their beautiful hearts, they are very much in their feelings a lot of the time. It seems easier with horses created in CAS so far for me. I'm finding a Free Spirited horse the most tricky to deal with. She's always feeling Cooped Up, despite being taken out and with the gate left open for her to go for a wander. She won't play with toys either. She got the Sad emotion stuck, but I found that exiting the game helped to shift it.

My Sims keep fruit in their inventory to hand feed them as sometimes that helps. It just puzzles me when all needs are met and the mare or the little foal are sad. They're on a 64x64 lot with toys and space. A Sim is with them all day too and they get on with the other horses.

I'm starting a new household in the next couple of days and I'm just going to add a horse from CAS and avoid the exchange. I've been careful with the traits of the horses I've adopted (I like that you can see those) but found it a horsey emotional minefield so far lol!

You should get a notification in the top right corner when you ask what’s wrong.

Though even if you don’t, interactions that will help should be marked - for example, if social is low, the social interactions have a red icon, or if the horse is sad actions like “cheer up” will have a blue icon.

Just a heads up on the horses who are low fun but won't play with the horse ball (which is the main source of fun for them I believe), the ball needs to be repurchased and replaced frequently.  I don't know whether it's bugged or needs to be tuned differently, but it stops working after the horses have played with it a few times. There's no way to tell by looking at it that it no longer works, but if your horse's fun is low and they won't go to the ball even if your sim calls them to it then try deleting and replacing it.

I buy a new ball every time I begin to play, I see low fun on a horse, or any time I open BB

@twistedstitchThat's genius! That explains why my horse played with the ball all the time when the household first moved into their new home, but now she won't touch it and she's always very low on fun. My Sim has been taking her for a gallop instead as she refused to play every time.
I'll try this tomorrow. I thank you and Buttermilk the sad palomino thanks you too!

Edit: this worked! I repurchased the ball and Buttermilk played with it all day. She also didn't need to be directed to do so, in fact she got out of bed to play with it when her fun was low and she was uncomfortable.

She is also having some interesting reactions to to wild rabbits and birds which was fun to watch.

Sometimes I get a pop up with what’s wrong, sometimes I don’t. 

a few reasons I’ve had for a sad horse, if it helps, are:

A needy horse who wants to be hand fed only (super annoying to keep running out to hand feed but he was sad every time he used the feeder. 

A horse from a champion bloodline, that was basically training herself in jumping and agility was sad every time she knocked her barrels or rails down. 

And as someone else mentioned if they go too long without being ridden they get sad or bored.

And last, for a while I had two horses that trained on their own and one that didn’t. The one who didn’t train was always sad that he wasn’t having fun…but he wouldn’t train or use the ball on his own and my college student sim did not have time to ride him all the time.