NET

17 Rather, he must acknowledge the son of the less-loved wife as firstborn and give him the double portion of all he has, for that son is the beginning of his father’s procreative power—to him should go the right of the firstborn.

Darby

17 but he shall acknowledge as firstborn the son of the hated, by giving him a double portion of all that is found with him; for he is the firstfruits of his vigour: the right of the firstborn is his.

KJV

17 But he shall acknowledge the son of the hated [for] the firstborn, by giving him a double portion of all that he hath: for he [is] the beginning of his strength; the right of the firstborn [is] his.