When I was considering buying my horse my partner and I talked about the fact that having a horse probably meant not having children due to both the time and expense of horse ownership. This was a very hypothetical situation because neither of us has ever felt any strong desire to have kids, but when I bought the horse it was shutting a door. Yes, it is possible to put my horse on pasture board or lease him out or even sell him, but realistically I wouldn't want that. When I realized that my choice was really between something I knew for sure would make me happy and something I probably didn't even want it became pretty clear what the best decision would be.
I grew up with a mom who had kids because it was expected and she didn't really consider that she had a choice. Some of those situations work out great and everyone's happy, but I know that if my mom had to do it over again she would not have children. This is clearly a huge reason why I wouldn't take the chance.
I have 6 horses and our first daughter is almost 5 months old. I have always known I wanted to be a Mum.
Not going to lie, it's not an easy thing. When I'm functioning on 2 hours sleep, bub has had a bad day and DH is away at work there are days where the last thing I want to do is go out and make sure the crew is fed and watered.
However, I probably would have completely gone insane if I had gotten rid of the horses before having our little girl. Sure I haven't ridden for a while, but just being able to go out and hang out with them for 10 minutes is a good break every once in a while.
Having said all that, like has been said, if you decide you don't want/have time for a horse you can sell it. That's not an option with kids so if you aren't certain that you want them, don't have them.