Dog left outside while family on vacation

My son (13) has spent the week with us (me 38f & my fiancée 38 m) in addition to his regular visits because his father and step mom went on a cruise and he had a break from school. During casual conversation with asked how his dog was and who was caring for him while the family was away. My son is responsible for feeding and watering the dog, and I was aware that it’s an outside dog who has 40 fenced acres. My son said the dog was doing well and I asked who was caring for the dog since the whole family was away. I was a bit surprised when I learned the dog had been left alone and had only been given extra food . The family was away for 8 days, and I don’t feel that this is responsible at all. Why not have a friend or Neighbor at least come by and check on the dog every day or so? I intend to bring this up to my son‘s father because I feel that it is very irresponsible and neglectful to leave an animal like that. I’m looking for suggestions and advice on the best way to bring it up in such a way where it is constructive and will actually help the dog get better caree. we also have two dogs anytime we are away from home. We make sure we have a dog sitter or reward them. This is not the type of treatment that should be modeled for a child and how to take care of animals, but I want to be able to bring it up to my son‘s father in such a way where it will be constructive and conducive and getting better care for the animal as well as better role modeling for my child as to how to take care of animals. Thank you in advance for any advice or suggestions.