Settlement Brahmins generate meat and hide.

[Aderod]

Settlement Brahmins now just generate fertilizer, I really think they also should generate both Brahmin meat and Brahmin hide.

Or maybe there is already mod that make this?

[BlazeStryker]

Brahmin MILK, as well, come to that.

[rsm000rsm]

Brahmin do generate meat and hide...as soon as you kill them, just as would be necessary in the real world. 

Seriously, though, as BlazeStryker said, brahmin milk would be more appropriate since, I think, brahmin are supposed to be mutated dairy cows. The bramhaluff from Nuka World look more like beaf cattle. They'd still require slaughter for meat and leather, though, if we're talking realism.

[BlazeStryker]

Unless we are dealing with something like Sim Settlements' Altairp's Animal Farm, a system of breeding and raising livestock would need to be worked up.