Yes, half of a small square. Believe it or not, just adding that much can DOUBLE the amount of feed in the grinder because it gets so fluffy. If I have the mixer over half full I watch the level carefully when I start adding the bale. I always grind it in last and let it mix for 5 minutes or so. The alfalfa pieces end up a little more than 1/4 inch in length. It keeps the hogs from gorging themselves on corn but the protein is high enough to make them gain. Also, if the feed doesn't have enough texture to it hogs will sometimes get ulcers. It helps avoid that.
We always did it growing up, so I have always done it too. I have used hay bales as well. It adds nice roughage and gives the chickens more to pick through. The last few times I have used hay as it was close at hand.
The chickens are crazy for it and some days it will double egg production. I think it is the minerals. The mix I do is about the same protein as bagged feed and has the same minerals. I have been hesitant to feed it as sole chicken ration but have been thinking next time I go to the coop I would pick their brain about it. I have a house of old layers so I might experiment with them.
If I am feeding out a steer it gets about 1/2 a five gallon bucket of it a day. The cows just love it - it is like ice cream for them. For whatever reason horses won't touch it. They are a little slow to try something new, though.
I don't know that the alfalfa adds a lot of protein. If I use hay I put in another bag of concentrate 40. The alfalfa maintains the protein level but the hay brings it down. With that in the mix it is beautiful feed, though.
I guess I have never thought twice about it - I just did it. I guess we did it growing up to save money. We didn't know any better and those animals were just fine. Sometimes we over think things in the enlightened age!