Shabbos 153b: If one is stuck on the road with his wallet, and has no non-Jew with him, he should place the wallet on the donkey. But then he is working the animal, and the Torah says, “You shall not do any work, you… and your animal!” Rav Adda bar Ahava said: He should place the wallet on the donkey while it is already walking.
Shulchan Aruch Orach Chaim 266:2: Some say that he should not urge on the animal by shouting at it as long as the wallet is on its back.
שבת קנג ע”ב: אין עמו נכרי ־ מניחו על החמור. והלא מחמר, ורחמנא אמר (שמות כ) לא תעשה כל מלאכהִ ־ אמר רב אדא בר אהבה: מניחו עליה כשהיא מהלכת.
שולחן ערוך אורח חיים רס”ו ס”ב: יש אומרים שצריך ליזהר מלהנהיגה בקול רם כל זמן שהכיס עליה:
Someone asked Rabbi Ben Zion Abba Shaul if it’s allowed to tell your dog to turn on the light on Shabbos. Based on an inference from a Gemara (Shabbos 19a), he concludes that it’s forbidden. However, he says there is a difference between telling a gentile and telling a dog. In the case of the gentile, there are two reasons, listed by the Shulchan Aruch Harav 243:1:
1) He is considered the shliach – agent of the Jew.
2) It is classified as weekday speech.
Therefore, on Erev Shabbos, although reason 2 does not apply because it’s not Shabbos, still reason 1 applies, and that is why one may not instruct a gentile on Friday to do work on Shabbos (e.g. delivering an overnight letter). But in the case of a dog, the animal cannot be your shliach. The only reason is that it’s weekday speech. Therefore, you may train your dog on a weekday to do melacha, such as turning on the lights for you whenever you enter a room.
Source: Ohr Letzion v. 1 Siman 23
[Why did Rabbi Ben Zion Abba Shaul have to resort to forbidding it because of “amirah” – similar to amirah l’akum? Why didn’t he forbid it because of the Torah prohibition of “mechamer” (doing work with your animal, which is forbidden even if you don’t lead it physically, only with your voice – Orach Chaim 266:2), or “shevisas behemto” (which is forbidden even if a gentile borrows your animal and works with it)?
Although this is not written in Rav Ben Zion’s teshuva, I heard (from Rabbi Moshe Zoberman) that he said that these two prohibitions apply only when you force the animal to work, such as by yelling at it angrily (see the Mechaber’s language “b’kol ram” and the Mishnah Berurah 266:1 “yigor”). But a trained dog can respond even if the owner asks it nicely, out of loyalty to its owner.]
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