As for protein content, there is not much of a difference between these crops. Besides, you can just about get any protein level you want within the limits of the species by harvesting at the appropriate stage of growth. Other differences to consider include palatability and soil drainage. Cereal rye and triticale are the least palatable species of small grains. Also, cereal rye does not tolerate poorly drained soils.
Ryegrass is much more suitable for such conditions.
Although cereal rye wouldn't be my first choice for a winter forage, it can be utilized under certain situations. The following is an update on some of the new products that will be used for weed control in corn in the near future. Keep in mind that some of these listed may not be available in 1998 but at least you will have some idea of what they are and what they do. My experience with Roundup-Ready corn is that you need to make at least two applications or use with a residual herbicide program. I will be making a presentation about Roundup-Ready corn at the 1997 Texas Plant Protection Conference in December.