Can chickens have reptile calcium/vit D supplements?

[LaynaDon95]

My hens used to be completely free range, but due to the rise in predator problems, they are always kept in the coop now. We are in the process of building a run, but it isn't completed yet. They aren't getting enough sun or calcium right now. They still healthy, nice bright combs, shiny feathers, laying on a regular basis, but their egg shells are getting softer. (The coop does get sun, and they get fresh veggies and grass on a regular basis, just not as much as they were used to.)
At wal-mart, I found a reptile calcium ascorbate/vitamin D3 powder supplement. I was wondering if that would be acceptable to add a little to their food to help comp for the lack they are getting naturally? I've tried giving them oyster shell, but they won't eat it. They never have, even when I was having a problem with shelless eggs, they wouldn't touch it. So maybe this would give them the calcium they need.
What do you think? Would this be safe to try?

 

[Hooligans7]

My hens used to be completely free range, but due to the rise in predator problems, they are always kept in the coop now. We are in the process of building a run, but it isn't completed yet. They aren't getting enough sun or calcium right now. They still healthy, nice bright combs, shiny feathers, laying on a regular basis, but their egg shells are getting softer. (The coop does get sun, and they get fresh veggies and grass on a regular basis, just not as much as they were used to.)
At wal-mart, I found a reptile calcium ascorbate/vitamin D3 powder supplement. I was wondering if that would be acceptable to add a little to their food to help comp for the lack they are getting naturally? I've tried giving them oyster shell, but they won't eat it. They never have, even when I was having a problem with shelless eggs, they wouldn't touch it. So maybe this would give them the calcium they need.
What do you think? Would this be safe to try?

As long as you don't overdose them, it should be safe to use, however, commercial layer pellets/crumbles/mash supply everything for hens to lay good-quality eggs, so supplementation wouldn't be necessary in most cases. What sort of feed are you using?

 

[LaynaDon95]

We use Dumor when we shop at Tractor Supply, CowTown (local) when we shop at CowTown, and Lone Star (also local) when we shop at Lone Star.
When they are free ranging, their feed is enough, but being cooped up, it just isn't cutting it. Their eggshells are starting to get too soft and if we don't start supplementing now it'll get worse. It's happened before.