I have heard of them doing this and yes it can have negative effects on them. I read once they do this in the wild for calcium. Also if your dogs are on a ivermectin heart worm treatment once a month, some does pass through there systems and into the fecal matter. ivermectin can be lethal to tortoises.
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Michelle 
www.AssortedSerpents.com
All things bright and beautiful,
All creatures great and small,
All things wise and wonderful:
The Lord God made them all.


