Here is a Bulgarian study on the subject.
I could be wrong, but It seems counter intuitive to give vitamin B during the treatment - if that is what you meant.
This is my thinking since the purpose of the treatment is to starve the protozoa of thiamine.
I have seen recommendations and I do the same to boost the B vitamins AFTER treatment.
Interesting. I'll have to discuss with my livestock vet sometime, see what the reasoning is. Thank You!