When we had his sister put to sleep, at home, I took the body over to him and showed it to him and let him smell her. He was alright for several days, then I went to visit my sister (fly to CA) and that's when he went off his feed. He slept in bed with me last night and is still refusing food, but I'm going to Costco to get his favorite, rotisserie chicken, hoping that he won't be able to resist. We do have other dogs, one female has been with him for 7-8 years, so I'm hoping that will help. And I haven't ruled out that something else could be wrong. We've never raised litter mates before.
Reignmaker, I too have had a Bullmastiff, wonderful dog. This guy is a chihuahua mix.
Thanks for the advise.