Grow2max is a probiotic mix for young birds. You can find it on
Amazon.
Chopped boiled eggs is an excellent supplement for young birds, or even adult birds. That is if you have extra eggs, and most of us do. Young tender clean sprouts is a good option for chicks. I range my adult birds, and the qty. required convinced me that it was not a practical option for me. Chicks on the other hand, do not require much. Both of these would be supplements, so a little goes a long ways.
Into the spring there is probably some young tender weeds in your yard that you can cut and carry. Young cleaned greens help add variety, interest, and entertainment to growing birds. Not to mention that there is something to be said for food that is alive.
As beneficial as sprouts can be, they are young tender plants. Don't neglect what is readily available and free for the cutting, early in the spring especially. Here I have a surplus of chickweed etc. while I am brooding chicks.
Karen, keep in mind that the intestines of commercial broilers are more fragile than what we might raise. They are genetically different animals. Also consider that the dietary needs of a growing meat bird is different than an adult bird.
Southern States mixes a breeder ration called Super Breeder which is formulated for game birds, but is an excellent feed for our breeding birds. Probiotics is in the mix, and I have had excellent results with this feed. Unfortunately, I cannot get it anymore. It is superior to RocknRooster etc. if you do not mind crumbles. It is a breeder ration. If it is possible, a breeder ration should be preferred for adult birds.
I would not come to recommending a ration without having been convinced of the quality.
I can no longer reliably get a breeder ration. I instead supplement with calf manna, and hulled sunflower seeds. Birds that do not have access to range has some fresh greens cut and carried to them accordingly. Again, a little goes a long ways.