Technically yes it's all they need. One of the most succesful sheep farmers I've met does exactly this. I only say technically because the ewes have to be in the right condition to utilize the feed and they must be started on it slowly. If the ewes are thin and pregnant I would doubt they have the stomach capacity to get enough hay processed to feed herself and her lambs. If she's too fat you run the risk of milk fever with the too readily available calcium in Alfalfa, especially in first timers and older ewes. If they've had a sheep mineral mix free choice and even some baking soda either free choice or mixed in, and the hay is introduced slowly mixed with whatever feed they are getting before over 10-14 days, it should work on ewes in condition score 3 +or - a little. Assuming the alfalfa is truely 18% protein plus you might want to feed a little whole oats (1/4 pound or less ea) to cool it off! Regardless making the ewes walk for their feed (all types) helps keep muscle tone up and digestion functioning properly. Penned ewes fed too well can be as big a problem as starved sheep.
