Horse Problems

Earlier today my brother and I rode our new horses for the first time. Although Dolly, my horse, wasn't too happy about her bit, we eventually got it on her and she was fairly calm. My brother on the other hand had some problems... once he got on Star, his horse, she began to buck and dance around and after a few seconds decided to lay down on him.

Any idea why this happened? I'm obviously a zero-experience rider.

Could be saddle fit, back pain, old bad habits or anxiety relating to the anticipation of pain or bad experiences, or really anything.

Make sure to work with a trainer as your first horse that was having an issue with the bit I would guess is either overbitted and/or in need of dental attention. The second horse I would blame saddle fit, possible need for chiro and/or massage work for a good adjustment, and if that isn't it (talk to a professional that can take a hands-on approach please) also check to see if the horse is reactive for possible ulcers (as i've seen horses with this issue lay down while being girthed or asked to move u/s), and check for any other physical issues. And if you are going to have an equine dentist out to check the first one's teeth, it would be a good idea to have this one checked as well.

I completely agree 110%.

Most likely it's some sort of back pain, something wrong with her teeth, or ill fittling tack.
I highly doubt she just wanted to be mean and throw him off.

I'm another one going for pain issue - particularly the fact that she went to the extent of laying down. Laying down for a horse is a very vulnerable position for a horse and they won't do it in a situation like this unless there's something really not right with them. My bet is on the saddle fit/back issues.
Did you have these horses vet checked before you got them? And have you had your tack fitted properly to them?

Agreed w/kayty. I only had one horse lay down - my late QH. But he was trick trained and he learned bc the damn horse was smarter than most people, that if he was bored with a rider and "played dead" people got off and the lesson was over.... lol! Smart ass. He never did it with me but he'd make it clear when he was bored if I put a beginner friend on him. Crafty s.o.b. Lol. But he was an exception. He also learned how to open people doors... and had made it into my house on one occasion. In the living room... yeah haha. So yes most horses won't lay down and from the bucking that is accompanying it im going to go with that it is pain (and not that she is trick trained like my old qh was haha).

Hmm... this sounds quite serious... see if something is wrong with the horses tack or call the vet

This could also be because she isn't getting enough exercise? (is she getting enough?)

This is also very silly behaviour and you should maybe lunge her for a bit before your brother gets back on

Being new to your horses, they are testing you out. They want to know what they can get away with. I would guess they are fairly young horses too?