Responsa for Bekhorot 52:50
בכור בניך תתן לי כן תעשה לצאנך
What is the reason? - Said R'Shesheth: Because it makes him appear like a priest who helps in the threshing floors.<span class="x" onmousemove="('comment',' For in our days a firstling is of no use until a blemish befalls it. As, therefore, the Israelite has to take trouble with the animal for fifty days, i the priest asks him to deliver the firstling to him during this period to look after, he thus saves the Israelite expense and labour, in consideration for which he takes possession of the firstling and thereby prevents any other priest claiming it. He thus seems to be on a par with a priest who helps with the threshing in order that he may receive the priestly dues for his services, which is forbidden. If, however, the firstling was blemished and the priest asked him for it so that he might eat it, this would be permissible.');"><sup>26</sup></span>
Teshuvot Maharam
A Jew, an ignorant person, intentionally inflicted an injury on one of A's firstlings. Is A permitted to slaughter this firstling?
A's firstling caused damage in a Gentile's garden and was detained by the Gentile without A's knowledge or consent. Must A redeem the firstling? How much ransom must he pay?
A. 1. All these people were guilty of various sins: a) They permitted the birth of a public nuisance. b) They perverted the will of the Lord who intended His 24 gifts to the priesthood to be a boon to them and not a nuisance. c) They have been guilty of despising consecrated objects. d) They derived satisfaction from giving a priests' gift to a particular Kohen. However, A can do nothing about it.
A cannot slaughter the blemished firstling since the person who caused the blemish, though an ignorant person, was nevertheless a Jew.
A must ransom the firstling, but is not obliged to pay more than its market value.
SOURCES: Pr. 78. Cf. Weil, Responsa 127; Isserlein, Pesakim 166.