Animals with low blood calcium can compensate by producing vitamin D with exposure to sunlight and thus, absorb calcium in the guy. (petsmagazine.com.sg)
It's caused by low blood calcium and can be brought on by poor nutrition during pregnancy. (dogcare.dailypuppy.com)
You may be asked to check for signs that would indicate low blood calcium (which occurs in approximately one third of dogs) and to give calcium and Vitamin D supplements. (brittonroadveterinaryclinic.com)