You will always risk bloat with most legume hay types. However, you can limit your risk by breaking them into feeding your alfalfa slowly over two or three days, building up to your full ration. Even without safeguards the risk is usually not very large unless conditions conspire just wrong. I've fed thousands of cattle alfalfa hay, turned cows out on active growing alfalfa fields (i.e. that last cutting that just didn't make it quite dense enough to cut and bail) and have only experienced bloat a couple of times. The last time it was cows grazing growing alfalfa the morning after our first good frost. I do know operators who have done the same thing to find 6 - 7 bloated (dead)cows the next day. As a commercial outfit we weigh the potential risk/losses against the known gain. I look at a the feed costs of starting to feed hay every day through the winter figured against the value of losing a few cows if I turn them out. In my case, the risk is always worth the value captured. Myself, when feeding alfalfa hay, I break them into the full ration over three days and don't worry at all. I also feed in a way to help insure they are not exposed to alfalfa when they are hungry and want to gorge themselves. (i.e. feed out frass hay first and/or feed a full ration before turning out onto alfalfa fields)
If you are operating with a small herd and losing a couple means a big loss overall, put out a couple bloat blocks out a few days ahead of starting to feed your hay. Any cow that uses the blocks will be safeguarded as long as she visits the blocks a few minutes each day. The medicated blocks will prevent the natural saponin forming the dense bubble broth that causes bloat. I think bloat blocks are running around $24 now. It's cheap insurance if you have a small number of head and can be relatively sure you can get them going on them, but still there are no guarantees.
