I killed the nightkin who was killing the brahmin...

anything else to this quest? im not getting any updates now and I cant tell the rancher my findings.. I just get a 'not yet' dialogue option.

Search his body... I think he had a note about why he was killing brahmin--maybe you have to read that to advance the quest?

I did all that. nothing. bug perhaps?

Let's put quest details and questions in the correct forum please.

Yep.
I'm not sure what triggers it, but I think it's a bug. I've done that little side quest three times now and this last time I hit the same problem as you. For me, the Nightkin shows up at the pen but doesn't attack the brahmin and remains non-hostile until/unless I attack. Once I do, I can kill him and get the note but when I go back to the farmer, all I get is the "Not yet" dialog option. I've gone back to two different previous saves (one right before getting to Novac and one auto) but no good.

Like I said, I'm not sure what caused it. As far as I know, the only thing I really did different from either of my other two games is recruit Boone before doing the rancher's brahmin quest.
If you're on the PC, someone may have a console fix for you. I'm on the PS3, so no help there. :shrug:

I had this bug once, when i killed the mutant while he is invisible and in the town.

I don't remember exactly what solution i have found, but i think i have travel some days and came back to loot him once again after the stealth boy effect was over.

I just did this unmarked quest without any problems. Shoot Nightkin (8x rounds from the service rifle), loot body, read note and chat with dusty.

Yes, every time I come to Novac I run down there to the rock beside the road, and the Nightkin might be there.
You can't see him right away - but look beyond (towards the rocket place) and see if there is a Glowing One.
If you do see a Glowing One, you know the Nightkin is back again.
He's pretty easy to spot (once you know he's there, but is shielded).
Trail Carbine, 4 in the head. Buh-bye...
Always has a holotape on him, 'Screaming Brahmin'.
I have collected 1/2 dozen of them so far, heheh...
And he is usually carrying a minigun with only barely 10% health.
I reported back to the rancher when I first cleaned things up - he said 'thanks so much, that was quick' etc.
It was all very simple - but not sure if they intended him to respawn over & over again, ad infinitum...
Regards

Worked fine for me...

Sounds like a script isn't firing.

I waited until he got to the Brahmin pen and Veronica smote him. Got the note and went back inside the ranchers house.

Was he actually killing Brahmin when you killed him? Or did you attack him before he opened fire?