The Goq- if the animal feed is chometz, you would not be allowed to buy it, since you are not allowed to OWN any chometz. If it is kitniyos , then you probably would be able to buy, since you are allowed to OWN kitniyos , but you can’t EAT kitniyos {unless you’re sfardi, and then you would actually be allowed to EAT the animal feed! =)}.
