It depends on what you want to know. A friend took his goat to be scanned just before Christmas at 42 days. From the scan they think she is definitely pregnant, but couldn't see how many kids there were. For him, although it is useful to know she is pregnant, it would have been better to know how many she was having, as she had 4 kids 2 years, and did them so well that she nearly killed herself. So it would be good if she wasn't having as big a multiple pregnancy again.
Our old vet used to scan ours if we took them done to the surgery, not sure if it was a dog scanner or a sheep one, but it did the job. Our new vet doesn't have the equipment (nor really the room).
Beth