Not to often I disagree with Dun, but this one I do. Timothy has really no feed value to a cow. Timothy is just a hair better than straw. I see your in the NW as well. We have access to better alfalfa than most in the country. I would continue what you are doing. The worst thing you can do, is to under feed. If your heifers calf at less than a BCS 6. Your going to be playing catch up. Calf size can be effected by feed, but your protein is only at 14%, fat and carbohydrates are minimal. If your heifers are getting fat, back off on the alfalfa. Last year I bought some rained on alfalfa. It tested at 13% for protein. I fed all last winter and most of my calf weights were moderate (65-85). Good luck and Happy New Year.