We continue with the ninth chapter of Tractate Bechoros, Mishnah 2, which further discusses the animal tithe. The Mishnah comes to clarify an important principle: Even though a person is obligated to separate a tithe from every tenth animal born in his possession over the course of the year - from the beginning of the month of Elul to the beginning of the following Elul - the obligation does not apply to all the animals he owns as a single unit, but rather to each flock individually. When the flocks are geographically distant from each other to the point that they cannot be combined, meaning that a single shepherd cannot watch over and pasture both of them, each flock carries its own separate tithing obligation.
To illustrate: A person owns two flocks, one in Beit Shemesh and the other in Eilat - a distance that a single shepherd cannot bridge - and each has fifteen lambs born that year. He tithes the ones in Beit Shemesh by themselves and takes out one from them, the tenth that exits the opening, and he likewise takes out one from the flock in Eilat. Even though he has thirty newborns in his possession, he gives only two animals for the animal tithe, because he has two separate flocks before him that do not combine. How this law works - this is the subject of our Mishnah.
The language of the Mishnah:
"Maaser behemah mitztaref kimlo regel behemah roah" - The animal tithe combines up to the full walking distance of the foot of a grazing animal - The laws of the animal tithe, regarding the definition of a flock that must be tithed as one, establish that whatever is within the grazing and wandering range of that flock combines. The literal meaning of the phrase is: the full walking distance of the foot of a grazing animal.
"Vechamah hi regel behemah roah" - And how much is the foot of a grazing animal? - How far are the animals permitted to graze and distance themselves? The measure is not how far the animals are capable of walking, but how far the shepherd is prepared to watch over them: eight mil in each direction. (A mil is approximately two thousand amos, roughly the length of a kilometer; the English word "mile" is indeed derived from it, but in halachah the measure is closer to a kilometer.)
Eight mil in this direction and eight mil in that direction make sixteen, and this is the language of the Mishnah: "Shishah asar mil" - sixteen mil. We thus find that all animals located within a range of sixteen mil from one another are considered a single flock; and if the two flocks are further apart than this, we have before us two separate tithing obligations.
"Hayah bein elu l'elu shloshim ushnayim mil - einan mitztarpin" - If there were thirty-two mil between these and those, they do not combine:
Seemingly, there is no reason for the Mishnah to specify thirty-two mil, since it would have been enough to say that more than sixteen mil do not combine. Rather, the Mishnah specified this number because of a special case it comes to teach us.
"Hayah lo ba'emtza - mevi'an la'emtza um'asran ba'emtza" - If he had a flock in the middle, he brings them to the middle and tithes them in the middle - When two flocks, flock A and flock C, are thirty-two mil apart from each other, they certainly do not combine. But if he has an additional flock, flock B, standing in the middle of the way - at a distance of sixteen mil from this one and sixteen mil from that one - then they all combine and join together, since they are all within walking distance of each other. Therefore, he brings them to the middle location and tithes the three flocks as one, because they are not separated by a distance exceeding sixteen mil.
The opinion of Rabbi Meir - "Hayarden mafsik l'maaser behemah" - The Jordan River separates for the animal tithe:
Rabbi Meir adds an additional point: Aside from the matter of distance, if the Jordan River separates between two flocks, they are considered two separate flocks for the purpose of tithing, and he tithes this one separately from that one. The basis of his reasoning is an exposition from a verse in the Book of Joshua - a technical matter that is not among the well-known verses in this context.
However, the halachah does not follow Rabbi Meir. In practice, the Jordan River is not considered a separation, and the two flocks do not become two separate tithing obligations unless they are located more than sixteen mil apart from each other.
In summary: In this Mishnah, we learned that the obligation of ma'aser behemah is determined by flocks, and the parameter for combining them is "kemelo regel behemah ro'ah" - sixteen mil, eight in each direction from the shepherd. Flocks that are thirty-two mil apart do not combine, unless there is a middle flock standing between them that connects them, in which case he brings them to the middle and tithes them as one. Rabbi Meir holds that the Jordan River also separates and divides between the flocks, but the halachah does not follow his opinion.