C : Care Questions

[GeckoX]

A couple questions...   I have been hearing that people feed their gerbils milk bones. Are those a good source of calcium (im assuming that from the name), or should I find another source? I add liquid vitamins to my gerbils' water, does that contain calcium? On that note, does anyone know what the nutritional value of the vitamin supplement is?   Secondly, I give my gerbils toilet paper rolls (or paper towel ones) to chew on. Is that sufficient enough for them to wear down their teeth, or do they need something more tough like a piece of wood?   Thanks, Jason