Every thing that opens the womb in all flesh,
which they bring unto the LORD, whether it be of men or animals, shall be yours: nevertheless the firstborn of man shall you surely redeem, and the firstling of unclean animals shall you redeem.
All Commentaries on Numbers 18:15 Go To Numbers 18
George Leo Haydock
Beast. The Rabbins restrain this to the ass alone, which they pretend was deemed the only unclean animal by the Israelites, in Egypt, when this law was established; and Moses indeed specifies it alone, Exodus xiii. 13. (Abenezra)
But we cannot doubt but that camels, and all other unclean animals, were to be included, if the Hebrews kept them; (Calmet) and those which were rendered impure by some defect, were also to be redeemed. (Menochius)