Save all of your eggshells until you have a enough to fill a sheet pan. I keep mine in a tub in the freezer. (I don’t wash them or do anything special to them, just throw them in the tub after cracking them open).
Spread on a baking sheet and bake for 15 to 20 minutes until they become dry and brittle.
Pulverize the baked egg shells in your blender or food processor until they are a fine powder. Add herbs and process again.
Here are some herb suggestions to add:
Rosemary - antioxidant and antibacterial
Ginger - stress reducer and helps circulatory system plus a study found that hens supplemented with ginger started laying eggs with a greater mass and also higher amount of antioxidants in the egg yolks.
Oregano and thyme - natural antibiotic
Turmeric - stimulates the digestive system, add 1/2 teaspoon
Sprinkle on your flocks feed daily. No need to spend money on calcium or vitamins.