Can the introduction of grit cause a bloody stool?

[Cadmansd]

I got 20 new meat birds and 2 days ago I introduced grit to them and they were just shy of 4 weeks old.
Yesterday I noticed a bloody stool on the pen and I ordered Amprollium, but through out the day I haven't noticed anymore.
I'm new to meat birds and I do have to say the amount of poop is staggering as is the amount that they eat and drink, I swear I can see them growing every day!
Should I administer the Amprolium as a preventive or should I wait?

 

[azygous]

With that many chicks, it's more likely one injured another and there was a bit of bleeding than it being from coccidiosis. Grit shouldn't cause any bleeding. If you had mistakenly given them adult size grit, they just wouldn't have eaten it.

But if the chicks have been on the soil outdoors and the weather has been warm and humid, then there may be some call for going ahead with the amprolium.