Depends on who you talk to. Several breeders I know are exploring breeding year round and others have been doing that for a while. Those that use an ultrasound seem to have found out that some of their girls begin developing follicles outside of our "usual" breeding schedule.
Most of the stuff I've seen talks about cooling in late fall (October-November time frame), putting them together a few weeks after you begin cooling, and then breeding till the females ovulate or a certain date, whichever comes first. I've seen the last date to breed as early as February 14 and other posts/books talk about going until April.
What does everyone else do?