They're never with us long enough.  If you've ever lost a horse or know someone that has, it is an unimaginable sense of grief that goes way beyond losing a pet.  Cards are blank inside but don't try and say too much.  A simple sorry, I'm here for you goes a very long way. Consider Susn Friedland's book called Strands of Hope, How to grieve the loss of a horse.  It is a book that has brought me and many, many others comfort in a time of great loss.