I am SOOOO very sorry for your loss! It's never easy to say goodbye to a beloved pet, and when it is sudden and no sickness was evident leading up to it, it is even harder to accept.
In a large dog, with foamy vomit present, my first thought would be gastric torsion and volvulus, or bloat.
When a dog bloats, essentially what happens is that the stomach and the spleen flip over on themselves and switch places. Within a VERY short period of time (1 to 2 hours) the intestines and spleen have their blood supply cut off and begin to die. If surgery is not done immediately to untwist the organs, death is certain. Because the stomach is essentially sealed off because of being twisted, the dog tries to vomit but can't, and all that they can manage is white foam. They drink, but the water cannot get down into the stomach and it comes right back up. That might be why his water bowl was empty.
The only way to be absolutely certain of what killed him is to have a necropsy done. Otherwise, your vet can do what is called an external autopsy where he examines the body as it is to see if there are any obvious bite marks or anything else that could have caused trauma to the body.
Again, my most sincere condolences on your loss.
Ghilly
Thank you so much for your much appreciated concern and "wet kisses" it's been a very difficult couple of days, especially for my husband they were best friends and constant companions. I immediately looked into the food however he didn't show the signs they talk about and we don't live in the states they outlined in the recall (we are in Arizona) I think I'll look up snake bites and they reactions, funny you should mention that my husband had a dream that a snake had bitten our dog a few days earlier. Once again thank you.
I am SO sorry for your loss of your family member. I send you big HUGS and my babies send you WET KISSES.
I am not a professional, but two things come to mind that you might consider. I don't know where you live, but we have had a very unusual winter and spring. We have had more than our share of rain, and have completely skipped spring and gone to early summer. With the water and the warm temps, the snakes are in great abundance, and the ER Vet told me they are seeing a lot of snake bites. The poison will literally cut off their breathing. If you have other pets, I would suggest taking him to your vet or an ER clinic to have them check for snake bites.
Another thing, is what kind of food have you been feeding? There has been an FDA recall on Diamond products for Salmonella, and some pets have died. Typically, you will notice these symptoms over a couple of days.
http://www.fda.gov/Safety/Recalls/ucm299606.htm
Again, I am so sorry.
Max & Mabi's Mom