Shabbos, Chapter 5, Mishnah 4. In Mishnah 2 we learned that a donkey may go out with a saddlecloth - the blanket that covers it to keep it warm - provided it was tied onto it before Shabbos. Our Mishnah teaches the other side of the law, listing the items with which animals may not go out on Shabbos.
The laws of the donkey:
"Ein chamor yotzei b'mardaas bizman she'einah kesurah alav" - when the saddlecloth was not tied onto the donkey before Shabbos, it may not go out with it.
"V'lo b'zog af al pi shehu pakuk" - even though the bell is stopped up and makes no sound at all. The reason: the bell looks like a device for attracting attention, and this was how an animal would be led to market to be sold, and one may not create such an impression on Shabbos.
"V'lo b'sulam sheb'veis tzavaro" - the "ladder" here is not a climbing device, but a kind of brace used for medical purposes whose shape resembled a ladder, and it was placed around the animal's neck. When an animal developed a chafing or a wound, it tends - as people do - to turn its head back and lick the site of the wound, thereby delaying its healing. The brace prevented it from turning its head. The Sages viewed it as a burden on Shabbos.
"V'lo bir'tzuah sheb'raglo" - an animal whose legs tend to rub against each other as it walks would have wide leather straps wrapped around its legs so that it would not be injured. With these too it may not go out on Shabbos.
The roosters:
"V'ein hatarnegolin yotz'in b'chutin" - colored threads that served as an identifying mark, so that they would not get mixed up with someone else's chickens; each owner had his own color.
"V'lo bir'tzuah sheb'ragleihem" - straps that were tied to the chickens' legs so that they would not jump about, ruin things and break utensils. With these too they may not go out on Shabbos.
"V'ein hazecharim yotz'in ba'agalah shetachas ha'alyah shelahen":
Sheep, and especially the male rams, have a fatty tail, which is sometimes so long that it drags along the ground. To prevent this, a small wagon would be made to roll underneath it and carry it. With this wagon too the males may not go out on Shabbos.
The ewes and the "chanun":
The ewes - the females of the flock - may not go out "chanunos." The chanun is a small piece of wood that would be placed in their nostrils to make them sneeze. And what benefit is there in that? Parasites and worms were commonly found in the animal's head, and the sneezing, with its sharp movement of the head, would shake them off.
And why was this needed for the females in particular? The male rams are in the habit of butting one another head to head, and through this the parasites fall off on their own. The ewes do not do this, and therefore the chanun would be placed in their nostrils, since it is a natural means of making them sneeze and thus removing the parasites. Even so, they may not go out with it on Shabbos.
The calf and the cow:
"V'ein ha'egel yotzei b'gimon" - the gimon is a training yoke. The calf is small and not yet fit for work, but one wishes to accustom it to lower its head beneath the yoke, and for this purpose this small yoke would be placed upon it.
"V'lo parah b'or hakupad" - a nursing cow, upon whose udders a hedgehog's skin would be placed to prevent other animals from suckling from the udders. With this too it may not go out on Shabbos.
"V'lo bir'tzuah shebein karneha" - even though the strap or ribbon around the horns is made for adornment, it is considered excessive adornment that is neither necessary nor customary, and therefore the cow may not go out with it on Shabbos.
The incident at the end of the Mishnah:
The Mishnah closes with an incident: the cow of Rabbi Elazar ben Azaryah would go out with a strap between its horns, against the will of the Sages, since this is forbidden. The Gemara explains that it was not his own cow, but his neighbor's cow; and since he was the rabbi of the neighborhood and did not protest her conduct, the matter was considered his responsibility, to the point that the cow was called by his name.