'Firstling' in the Bible

Every firstling that is born in thy herd and in thy flock -- the male thou dost sanctify to Jehovah thy God; thou dost not work with the firstling of thine ox, nor shear the firstling of thy flock;

His honour is a firstling of his ox, And his horns are horns of a reem; By them peoples he doth push together To the ends of earth; And they are the myriads of Ephraim, And they are the thousands of Manasseh.