Okla. Stat. tit. 4, § 341

In all cases wherein any shipper of livestock has contracted with any person, firm or corporation for the use of feeding pens or impounding pens in stockyards in the State of Oklahoma wherein said lessee keeps livestock for the purpose of disposing of the same to packing plants or otherwise, said lessee shall have the right and is hereby authorized and empowered to furnish feed for the purpose of feeding said livestock without purchasing the same from the lessor of said pens or any other person.