According to Judaism the first-born males were given a special status. In Deuteronomy 21:15-17, the oldest son receives a double portion of the inheritance. Traditionally the first-born belonged to God: “On the day that I slew all the first-born in the land of Egypt, I consecrated for my own all the first-born of Israel born of man and beast” (Numbers 18:16), paid to a kohen (priest) on the thirty-first day after birth, the child is ceremoniously returned to his father.
The object of this ceremony was that since Jehovah had delivered the first-born of Israel they should be sanctified to him. The fundamental element upon which this sanctification rests is evidently the representative character of the first-born, standing for the entire offspring. Moreover, the first-born of newly married people was believed to represent human vigor.
First-born animals should also be given to a kohen. First-born males should also observe the Fast of the first-born on the 14 Nisan, the day before Passover. This is to give gratitude to God for sparing the Israelites in the tenth plague, but this custom has largely disappeared. The detailed laws are in the tractate Bekhorot in the Mishnah, et al. A.G.H.
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, pp. 346-347
Unger, Merrill F. Unger’s Bible Dictionary. 3rd. ed. Chicago. Moody Press. 1985. p. 367