Li-zchus - 

R' Moshe Yehuda Hanus

R' Shmuel Stein 

R' Chaim Schreck 

R' Eytan Feldman

R' Avromi Sommers

For much success in all they do together with their families

The Shulchan Aruch [448-7] wrote that it is forbidden to give your animal to a Goy on Pesach if you know that he will feed the animal chometz. The Gra writes:

"ודוקא בחמץ כמ"ש בירושלמי הנ"ל אם לכלבו ההן איסור הנייה, ועי' תוס' פ"ב דפסחים כ"ב, ב ד"ה ואבר". 

In other words, the Gra explains this din based on the Yerushalmi that says that one may not feed איסורי הנאה  to an animal of hefker and the Gra comments that this איסור related only to chometz [as the Mekor Chaim we saw writes, that this din doesn't apply to other איסורי הנאה]. The Gra referenced the Tosfos in Pesachim from which we can prove that the איסור of the Yerushalmi doesn't apply to other forms of איסורי הנאה. [Tosfos there says that one may hand a Goy אבר מן החי belonging to the Goy if not for the איסור of לפני עור. This proves that one may feed a Goy - and animal by extension - איסורי הנאה]. 

But the words of the Gra are very difficult to comprehend. The Yerushalmi is talking about feeding chometz to a HEFKER animal. The Shulchan Aruch that the Gra comments on is talking about having a Goy feed YOUR animal.     

The explanation of the Gra may be as follows: The Shulchan Aruch is talking about a case where the Goy is obligated to feed the animal of the Jew. If so, when the animal is fed by the Goy it is not considered הנאה for the Jew because as far as he is concerned it doesn't matter whether the Goy feeds the animal איסורי הנאה or other food. But we should still forbid this on account of the fact that one is not allowed to be the cause of a hefker animal eating איסורי הנאה [as taught by the Yerushalmi]. By giving his animal to the Goy who will feed it chometz the Jew is guilty of this infraction!? 

On this the Gra comments that this איסור applies only to chometz and not other איסורי הנאה.  That explains the ruling of the Shulchan Aruch forbidding one from giving a Goy his animal if the Goy will feed it chometz.

Question: Does the איסור to give a hefker animal to eat have a shiur? Shiurim were given only to Jews and not to בני נח [that is why the Rambam paskens that a Goy is not allowed to eat even the slightest amount of אבר מן החי - Melachim 9-10]. Since an animal is not a Jew, it would seem that the איסור doesn't have a shiur and any amount is אסור. 

According to this it would emerge that when a Jew eats less than a shiur of chometz himself, he would be transgressing this איסור. He is not transgressing the איסור of eating chometz but IS transgressing the איסור of causing chometz to be eaten [i.e. by himself] which in other cases applies to feeding a hefker animal. The principal forbidding one to feed a hefker animal is that one is not allowed to cause chometz to be eaten [as we discussed in the past]. Eating chometz himself is no better than giving it to the animal. 

If what we wrote is correct, then we can shed light on a perplexing Yerushalmi [Terumos 6-1] that says that even though Reish Lakish argues with Rav Yochanan and holds the חצי שיעור is מותר מן התורה, he agrees that when it comes to איסורי הנאה, a חצי שיעור is אסור. The Yerushalmi offers no rationale for this. Based on the foregoing, maybe it is because Reish Lakish holds that the איסור to eat forbidden food yourself requires a shiur. But the איסור to cause איסורי הנאה to be eaten has no shiur and thus even a חצי שיעור is אסור. [This would mean that the איסור applies to all איסורי הנאה and not only חמץ as the Gra claimed].    

[עפ"י תורת מורנו הגרח"ש זצ"ל]