Its not good to be around sheep because they can carry a virus I think that can cause miscarriage. That is what we are warned about in my country because there are lots of sheep.
I've been around my horses both pregnancies. With my first I was also around goats, donkeys, chickens and cattle (I helped deliver a calf when I was in my third trimester!). Physicsmommy is right, you need to be careful with medications. Don't use fly spray, have someone else do that. Once it's dry you can handle the animals. Of course, use good safety practice so you don't get physically injured. I stopped riding this time around 30 weeks.
My understanding is yes but there are somethings to be careful. I wouldn't handle any of the medicine or supplements given to them as some can be a potential problem. I Aldo wouldn't spray them for flies and such let someone else. And of course the obvious is most livestock is much larger than us and can physically harm if not careful. I was around cattle recently with out any problems I just stayed away from the most dangerous parts when they were being worked. As always check with your doc though and find any info on the particular type of livestock you will be around.