But the rabbis would not condone this conduct. They ruled that if the kohen intentionally, even if indirectly, injures the animal, a penalty would be imposed that would render the animal permanently prohibited to the kohen. The kohen who intentionally caused the injury to the animal would never be permitted to slaughter it or derive any benefit from it at all, until such time as the bechor either developed a blemish on its own or was accidentally blemished.
In order for the bechor to be free of its bechor status, the blemish had to be both accidental and permanent. A temporary blemish that would heal over time did not free the animal of its bechor status. So great was the kohen’s temptation to deliberately injure the animal that safeguards had to be put in place to make sure that each claim of an injured bechor was legitimate. Accordingly the rabbis legislated that only a special expert, called a mumcheh bechorot, would have the jurisdiction to decide what was and what was not a genuine blemish. The kohen who claimed the blemish was both permanent and inadvertent would be obliged to have the matter adjudicated by the mumcheh bechorot.
To qualify as a mumcheh bechorot one required many intense years of study and training in both halacha and veterinary medicine. The Talmud relates that Rav spent 18 months among herdsman to learn which blemishes were permanent and which were temporary. Today, except for obvious blemishes apparent to the untrained eye, such as a missing limb, there is nobody with the knowledge required to determine what blemishes are eligible to remove the bechor status.
In view of the fact that the laws of bechor are still applicable today, the absence of a mumcheh bechorot means there is little a kohen can do with the bechor behemah tehorah other than keep it around until it develops or incurs a blemish by itself with no human intervention. But as we have seen, this is problematic because people may unwittingly make use of the bechor for secular purposes either because they are oblivious to the laws of bechorot or because they are unaware that this particular animal is a bechor.
Therefore the rabbis have devised a way whereby the bechor behemah tehorah today will not be born in its sanctified state. This is achieved by selling a part ownership in the mother, before the birth of the firstborn, to a non-Jew. Since it is only the firstborn of an animal, owned solely by a Jew, that renders the firstborn sanctified, it follows that if the mother is partially owned by a non-Jew, the firstborn is not considered holy at birth and is free for secular use.
Another way of achieving the same result, also sanctioned by the rabbis, was to inflict a blemish in the animal before it is born and while still in the birth canal of its mother.
Raphael Grunfeld’s book “Ner Eyal on Seder Moed” (distributed by Mesorah) is available at OU.org and your local Judaica bookstore. His new book, “Ner Eyal on Seder Nashim & Nezikin,” will be available shortly.