Question: Why is it halachically permissible to tell a non-Jewish store owner to provide chometz food to your workers and you’ll pay for it on Pesach but you can’t tell him to give chometz pet food to your cow, etc. on the farm that you can slaughter?
Background:
A. Mishna Berura (448:7:29-33) it says that it’s forbidden to give your animal to a non-Jew on Pesach to feed it if you know he’ll feed it barley chometz. It doesn’t make a difference whether he gave it to the non-Jew for free or is paying him to feed his animal it’s forbidden because he is getting benefit from the chometz that’s being used to fatten up his animal. Chometz, even belonging to a non-Jew is forbidden to benefit from. However if the non-Jew did feed the cow chometz, the meat from the cow isn’t forbidden to the owner after it is slaughtered.
B. The Mishna Berura (550:6:16-19) says that halachically one may pay a grocery store belonging to a non-Jew for providing food to his slaves/workers on Pesach even if it’s chometz even though the Jew is supposed to be supporting his workers and benefits from them being healthy and strong to be able to work for him. (Those that argue only say it’s forbidden because one is paying his workers/slaves with forbidden benefits.)
Answer: The Nishmas Adam says (see Dirshu footnote 104) the point of feeding the slave isn’t to fatten him up but to give him energy to work therefore the benefit the master gets isn’t from him being filled with the chometz but the work that the slave does for the master, where as technically the animal is being fattened by the chometz and therefore it’s a juicier meat which one will benefit from when he eats it therefore it’s forbidden. However the reason why the meat is edible if done is because of the rule of “ze vinegar gorem” if both permissible food and forbidden food was used to fatten the the animal then it is permissible because can get benefit from both, you just shouldn’t ideally work in that fashion.