Oh, yes, you can breed AI without an ultrasound. True, it helps to know the size of the follicle, but no, you do not need to ultrasound. In fact, we don't ultrasound our own mares when we breed them. You simply watch them and gauge the length of there cycles just like you would using live cover. We watch and count from when they first show signs of heat, and on or about the third or fourth day, we palpate the cervix. When a mare is ready to be bred, the cervix will be very open and you can feel that with your fingers. We go ahead and collect the stallion and breed her. If the cervix is not open, she is not close to ovulating. We wait and watch her heat signs (just like with live cover) and check her in another day or two.
Now this is with the stallion on the place...if you are shipping semen, yes, I would ultrasound. You don't want to order a shipment and miss the ovulation, although you do have a certain amount of time after ovulation that you can inseminate and still hit them but it's risky. When you pay for semen you want things perfect.
I have heard the same about keeping a mare bred every year to retain her fertility. I don't know, I guess I have a 21 year old that we can't get to sustain a pregnancy at all...she takes right away but loses it before the second or third month. I will find out this next spring on my 19 year old, we haven't bred her for two years because of the drought...so we're going to try again in 2007...she's coming into regular heat cycles so we will find out if she takes or not.