Gabe -- Tractor Supply caters to horse owners. The brand of hay pellets that they carry is Standlee. Standlee is a large company in Idaho that markets several types of hay products from three different types of hay: Timothy, Orchard and Alfalfa. Timothy and Orchard are grass hays. Alfalfa actually isn't a hay at all, but is a legume. Many horse owners like to feed their horses Alfalfa, but the truth of it is that Alfalfa is pretty rich, and has to be fed with care. Mixing it with a grass hay is one way to not over-feed Alfalfa -- and so Standlee offers a pelletized version of the Alfalfa/Timothy mix. Standlee offers these hay products in several different formats: pelletized, cubed, shredded and regular bales. Not all retailers carry all varieties. Our local Tractor Supply stores carry the pelletized and the cubed. I use the pellets myself (of Timothy and Orchard -- no Alfalfa).
And there is more than you ever wanted to know about hay pellets.
For your purposes, you want the plain Alfalfa pellets. The Alfalfa/Timothy won't hurt anything, but you're paying for 40 lbs. of Alfalfa and getting 20 lbs. because it's mixed. See? So just wait until they have the plain Alfalfa back in stock. If they don't have a spot for it in your TS store, tell the store manager that you just want plain Alfalfa pellets -- he can probably order it for you.