Rashi on Deuteronomy 28:4/רש"י על דברים כ״ח:ד׳

1שגר אלפיך means the young of thy cattle which the animal casts out (שגר) of its womb.

2ועשתרות צאנך — Understand this as the Targum does: the flocks of thy herd. Our Rabbis asked, “Why are they (the flocks of sheep) called עשתרות? Because, replied they, they enrich (מעשירות) their owners (through the sale of their wool, etc.) and make them strong as עשתרות — which are strong rocks (Chullin 84b; cf. Rashi on Deuteronomy 7:13).