Hello and thank you for your question,
I have two answers for you, and I hope both will be helpful. The first is to call the the company on their toll free number at 1-800-233-1067 and ask them. They should have that information readily available and it's always good to have a second opinion.
The research that I found says that Preen with trifluralin has a low toxicity to mammals, but it is bad for aquatic animals like fish. A rabbit or a dog would have to ingest more than 2000mg for every 1kg of rabbit or dog. This means that applying it in your yard at the labeled/legal rate, should not cause a serious hazard to animals. As with any pesticide, animals (including humans) should not eat it, or get it in their eyes, and if they get it on their skin, it should be washed (which might be tricky with a wild rabbit).
This pesticide does carry some risk, but research indicates it is a lower toxicity chemical than 2,4-D which is a commonly used weed killer for home lawns. I would still call the 800 number above and ask them the same question you asked here. That way you have two independent sources saying the same thing, which always reassures me when I have questions.
I hope this helps, and please don't hesitate to ask if you have any more questions, or if I wasn't clear.
Thanks for contacting us!