6-7 years ago I had a chocolate lab female named Belle. My wife and I were watching some early season college football one night and at halftime of the game I decided to feed the dogs their evening dinner. I went out on the porch and Bo ran up on the porch like usual and Belle just sat there at the bottom of the stairs looking up at me with a pitiful look in her eyes. I called her and she wouldn't budge so I said in a stern voice "Come here" and she tried to come up the stairs but looked like a drunk falling over and struggling to get her legs under her. I went down to the bottom of the stairs and picked her up and carried her into the house. She kept licking my face over and over as I carried her up the stairs. I put her on a blanket and called the vet and they told me to watch her overnight and if she wasn't any better by Monday morning to bring her to their office. I guess about 20 minutes later she layed her head down and stopped breathing and her eyes glazed over. I started looking her over and found two fang marks about 2 inches apart on her back leg which told me what I needed to know.
I killed that timber rattler on the road in front of my house the next morning.
Belle saved me from getting bit one night in the yard. I pulled in from work about 3 am and got out of my truck and was walking around the front of the truck. It was black dark outside because my wife turned the porch light off so I couldn't see anything except for one little spot of light coming from the kitchen window. I hear Belle coming through the backyard to greet me and when she got in the light from the kitchen window a few feet from me she just jumped back and stood there staring. I eased back to my truck and got a flashlight and sure enough a two and half foot copperhead was coiled up right in the entryway to the backyard and I would have probably stepped on it. I didn't want to put off a gun in the driveway at 3 am so I pinned it's head down with a stick one of the dogs had drug up in the yard. Once I had the snake in hand I took it around to the back of my truck and got a pair of pliers and crunched it's head with those. I wound up keeping the skin and made a hatband out of it.
Dang....sorry to hear about your dog. Crazy story. RIP Belle.