I am sorry to hear Gator broke a nail too. Ino's vet said it may have to do with the moisture change during winter and I am thinking now that may be a major factor. It definately is something that appears to be more common in winter (atleast that holds true for my boy and it seems that it is more common in the dogs residing in the northeast or northern states during the colder months- from looking at the posts).Ino has never had a nail break during the warmer months. I have to keep on top of dremeling Ino's nails and inspecting them daily for jagged edges so I can round them off or clip areas that need it so he does not break them when we go out on our walks. I know for Ino, digging and falling through the ice layer on top of the snow are 2 things that have caused his breaks- but something definately has made them more brittle than they should be. The suppliments do seem to be helping also because his breaks are not as common and are not as bad when they do occur now.
All I know for sure though is it sucks when they do break!!!