Horse feed and eggs

[allysponies]

I have 2 buff orpingtons who lady eggs. The other 7 NH reds/Americaunas haven't started yet. They all scratch around in the horse stalls and eat the feed from the buckets. They get plenty of layer crumble and vegetables odds and ends.
My question is, are the various supplements the horses get bad for the egg quality? As in safe for us?

 

[Fanci Feathers Marans]

My hens do it all the time, and I don't notice a difference.
As far as supplements go, we use hoof supplement with the same results.