ok honum gaf hann alla ina beztu gripi sína hálfa við sik.
and - to him - gave - he - all - the - best - animals - his - half - with - himself
and he offered half of all his best livestock to him.
 
I was interpreting this to mean half of the whole herd.  But as I get into the next passage, I see that actually he is dedicating half of each ANIMAL to Frey, so I guess this should be:
 
and - to him - gave - he - all - the - best - animals - his - half - with - itself
and he offered half of each of his best animals to him.