According to the laws of the Torah one is forbidden to muzzle an ox which is threshing and so limit the amount the ox can eat during the threshing. (To separate the wheat from the chaff they would have an ox walk on the stalks of wheat) One must, instead, allow the ox to eat the wheat which he is threshing, for in the Torah it is written, “Do not muzzle the ox while it is threshing” (Deuteronomy 25:4).
According to one of the Sages, the prohibition against muzzling an ox while he threshes applies only to an animal which uses four feet to thresh. If the animal threshes with only two feet, there is no prohibition against muzzling it. (As though it feels no pain?)
One Sage asked another: What is the rule for a person who uses geese or chickens to thresh? (They only have two feet.) Since they do not thresh using four feet as do oxen, there may be no prohibition against muzzling them during threshing, but since they only have two feet and they use both to thresh, they may be considered as the oxen who use all their feet to thresh, so one may be prohibited to muzzle them. (This question is not resolved in the Talmud.)
(Babylonian Talmud, Tractate Bava Metzia 91b)