Hi, thanks for your question!
The answer is, "that depends." What kind of grass is already existing in your pasture and what shape is the stand in? What class of cattle are you grazing and what is your stocking rate? An in-person visit would definitely help to get a better feel for what is best for your situation.
However, as a short, generic answer...typically I recommend orchard grass or an orchard grass/clover or alfalfa blend, again, depending on what your current situation is. We are now out of the window of opportunity for spring seeding. The next opportunity for grass to be seeded is from mid-August through the end of September. I would also recommend you have your soils tested (a free service for land in Shelby County through our office) before investing in seed.
I would love to visit with you regarding the specifics of your pasture in order to make more specific recommendations. You can give me a call at 502-633-4593 or email me directly at firstname.lastname@example.org.