Every firstborn that is born in your herd and in your flock, the male, you shall consecrate to Hashem your God; you shall not work with the firstborn of your ox, nor shear the firstborn of your flock.
English: "With the firstborn of your ox" — with the firstborn of your ox you may not work, but you may work with a human firstborn.
On the daf / in context: The prohibition of labor applies only to animal firstborns, not to a human firstborn (who once performed Temple service before the selection of the kohanim).
Type of Learning
Derash on the verse (Bekhoros) — human firstborns are not subject to the work prohibition.
What Is Learned
The prohibition against working a firstborn applies only to animals, not to a human firstborn.