Have to agree with everyone who says your OH should not be laying down ground rules. Yes consider loaning whilst you are pregnant/baby is young but do not be forced into selling your horse. My ex left when my daughter was 6 and son 18 months, at that time I had a pony, donkey and 4 dogs. The menagerie has increased by another pony and a horse now. The animals have of course increased my work load but they have also been my lifeline on many occasions. I think you should sit down with your OH and explain how you feel about parting with your horse permanently, and if he refuses to see your point of view have a long hard look at the relationship.
Just to be counter cultural here, it would depend for me. I can be unrealistic especially financially, and 'head in the sand' - so search your soul - I don't agree with others here that your OH is necessarily evil for setting 'ground rules' - IF you are like me, and inclined to go 'oh, it'll be alright!' when it patently won't!
It's ok for them to say 'oh I wouldn't stand for that' if they can afford it!
Do you need someone to set ground rules for you or not? That's the question!
Phew...I think everyone needs to take a deep breath here. OK, the 'groundrules' word is a nasty one...but lets accept that the OP loves her husband, her husband loves her, they both want a baby and a life together...and look at this without the over-reactions.
Firstly, I agree that looking for a loan home is a great solution.
I want to stick up for the husband a bit here. I take it he isn't horsey himself? So, I think you need to take into account that
1) Lots of families struggle financially when they have their first baby and the mum stops working. Babies are very expensive on top of a drop in income. Horses are also a very expensive luxury. I know what you are all thinking, but yes they are a luxury. What with the recession etc right now, he may just be scared stiff at the financial implications of your giving up work and having to support 3 people - so he's thinking you won't be able to afford a horse as well. He might be right. So you could talk to him about loaning instead. It is not as simple a solution as selling - but it still reduces the financial burden on your family for a while. I also assume you'll be getting some maternity pay? Does he know this and is he taking it into account when thinking about this? (Of course, if he earns loads of money and is just being tight about paying for something personal for you while you aren't working, then you do have some problems!)
2) Does he understand the bond you have with your horse? He may not realise this is anything different to asking you to give up a second car or something. It seems obvious to us, but it isn't to others.
when I was 16 I had to give my loan pony back to the owner after 2 years. I was heartbroken and I can remember laying on the sofa sobbing while my parents looked at me dumbfounded. Despite having been pony-mad from the age of 4, ridden my whole life, spent all my spare time at the stables, having favourite ponies, and then having the fantastic experience of loaning my 'own' pony, they never twigged that there was any emotional attachment with horses. They'd always supported me, but thought it was just the riding as a sport I enjoyed. I had to tell them 'to me it feels the same as if we were getting rid of our family dog' and finally they understood. They are animal lovers themselves, but had had no concept of how riders feel about their horses. Perhaps your husband needs a bit more explanation about how this will make you unhappy...