I have used hot pepper in winter to increase internal heat and laying improved that day careful to add just a few jalapeno peppers in their forage food and let them chose when to peck. I have also used a clove of garlic dropped in their water and other times cider vinegar alternating to help...
I used sand before and the girls would dust in it but several ate it and within a couple of days died I was told it had glass in the making of the sand and this could cut their insides so I removed it.