I am not sure it prohibits anything, but the seller of the animal is reserving the right to clone any and all animals from that "cell line", meaning (at least scientifically) that they can clone any offspring from that animal on down the line.
Example - You pay $10,000 for a heifer. You work hard, take her to 20 shows and win all of them and she actually has a calf. The seller of the heifer can come to you and get DNA on her and her calf and clone them. So all your hard work just got them a bunch of publicity so they can create some more of the heifer and sell them for big money. And you did all the work!
As you can tell, I am NOT a fan of sellers retaining flushing, cloning or cell rights.