This Vedic Mantra has no concern with eating beef or any non-vegetarian food. Devta of this mantra 10/85/13 is “SURYA VIVAHA” So, this mantra relates to marriage.
सूर्याया वहतुः प्रागात्सविता यमवासृजत् । अघासु हन्यन्ते गावोऽर्जुन्यो: पर्युह्यते ॥
The mantra states that in winter, the rays of sun get weakened and then get strong again in spring. The word used for sun-rays in ‘Go’ which also means cow