8. One who has a Gentile helper who rides the animal out into the public
domain in order to allow it to drink, does not have to prevent him from
doing so on Shabbos. The reason for the prohibition against riding on
Shabbos, is not because the person is considered a burden (carried by the
animal) (1), since "a living being carries itself" (carrying a living being
on Shabbos is only a Rabbinic prohibition, which the Sages did not apply to
one's animal) (2). Rather, the prohibition against riding applies to the
rider himself, that is, a Jew is not allowed to ride on Shabbos (3). Thus,
this prohibition does not apply to a Gentile.
[There is no prohibition against the Gentile's] placing of a saddle or
saddlecloth on the animal to enable him to ride it, for they are not
considered entities in their own right, but rather auxiliaries of the
rider. He may not, however, place other articles on the animal (4).
(1) As we've seen, one may not allow one's animal to carry a burden on Shabbos.
(2) In other words, according to Biblical law, because a living being
carries its own weight to a certain extent (sleeping babies are always
heavier to carry!), one does not violate the prohibition against carrying
on Shabbos, when one carries a living being on Shabbos. The Sages later
made an enactment prohibiting a person from carrying a living being on
Shabbos, but did not extend the prohibition to one's animal (See Shulchan
(3) There is a rabbinical prohibition against riding or even making use of
an animal's body on Shabbos or Yom Tov (Beizta 19a). The reason given by
the Talmud Bavli is a concern that one may break off a tree branch (a
biblical violation of Shabbos) in order to strike it while leading it along
or riding it. According to the Jerusalem Talmud, the reason for the
rabbinical prohibition is a concern that one may come to lead the animal
into a public domain with a load on its back, which we saw is Biblically
prohibited (Aruch Hashulchan 305:16).