An easy way to collect aurochsen hairs is to do it from water, but this isnt always an option. you can also do it easily with sign fences.
first, try to get each auroch in its own separate fence, dont worry if you cant do this to all of them its not that big of a deal. make sure your fences look something like:
XXXXXXXX
X-------X
X------X
X-----X
X---X
X-X
X
Or something like that. when the aurochsen are positioned right, you can grab the hairs through the diagonal fences. pulling hair often causes the whole herd to become aggro, but sometimes, they wont. its best to not take any chances and just pen them in though. be careful, as under the right circumstances, you can accidentally slip through the fence an get your shit stomped. a good way to get them into position is to go to one side of the aurochsen, and when it moves towards you go to the other side to get it jammed in the gap. kind of like wiggling the pin to get it further into the hole. this same method of grabbing hair can be used for taming later on as well.
also, if you want to get metal early on, try to lay claim to a cave as quick as you can find an unclaimed one and dont let it go.