Several different things can cause this. First, the cow could have been in labor for too long and could have suffered internal injuries. It's best if the cow is not in straining labor for more than four hours. The calf could have been breech or backwards and the cow would be unable to work the calf out. Then due to her straining, she could have torn her uterus or ruptured an artery. Both of these could lead to massive blood loss, shock, and ultimately sudden death. The only way to diagnose the actual cause of death is to contact your veterinarian.
