2,730. A Vow to Be Like Nosar or Piggul

Hilchos Nedarim 1:12

Let’s say that someone declares produce to be to him like nosar (a sacrifice beyond its permitted time), like piggul (a sacrifice offered with improper intentions) or like meat of a sacrifice that was rendered impure. In all of these cases, the produce becomes prohibited because the person has in any event equated it to the meat of an offering.

Hilchos Nedarim 1:13

If someone declares produce to be to him like animal tithe (maaser beheima), it is rendered prohibited because the sanctity of maaser beheima is placed upon it by people. If he declares it to be to him like a firstborn animal, it remains permitted because firstborn sanctity isn’t allocated by people and these animals can’t be assigned with a vow, as per Leviticus 27:26, “One may not consecrate it.”