Furthermore she states, "several researchers from the National Institute of Rheumatic Diseases in Piestany, Slovak Republic, conducted a study on eggshells in 2003 that showed eating eggshells can prevent and treat arthritis and osteoporosis in humans and animals."
I've also read that eggshells contain chondroitin sulfate, which is excellent for dog and human joints. While I know the calcium is a good thing, it's really the joint aids I'm looking for in the eggshell powder because both of my dogs are now seniors with arthritis, one of them with severe arthritis in her front leg due to dislocations she suffered at birth. I know what it's like to be in severe pain and I can't bear thinking my little happy-go-lucky pooch hurts. Fortunately, she's doing really well with medications, a treadmill, laser therapy, and a good diet.
Grinding eggshells to flour-like consistency is a breeze in my Vitamix, if you don't have such a powerhouse, you can try using your blender (but might not get such a fine grind), do smaller amounts in a spice grinder, or even use a good old mortar and pestle and a lot of elbow grease.
Whether you choose to take eggshell powder for yourself, or your dogs, please consult your doctor or their veterinarian for advice on of this is a good idea, and proper dosing.
Information from: http://dogcare.dailypuppy.com/dogs-eggshells-2716.html
Step 1: Prepare Eggshells and Grind
You can save the shells from soft or hard-boiled eggs, and fresh eggs you use, wash them in soapy water, let them air dry and store in a sealed bag or container until you've collected enough to grind. I grind about 18-24 shells at a time, this yields about 1/2 cup of eggshell powder.
Place as many eggshells as your container will hold, obviously a spice grinder will only hold a few. You can crack them further to fit inside the container or make grinding easier at this point.
Grind away, this takes about a minute on speed 10 in my Vitamix. You are looking for as fine of powder as you can get. Many dogs would eat a hard-boiled egg, shell and all, but I feel the powder is easiest to blend into their food (and if you are using it yourself, mix this right into your protein shake or in my case, I'd probably add it to a s'mores milkshake!).
Step 2: Store and Use As Needed
My small pooches, Bay-Li and Car-Li get 1/4 tsp. on their dog food, check with your vet on dosing for your dog.