Hello and thank you for asking your question. My name isXXXXX will try to help.
I would buy some canned dog food. The first day, mix a spoonful of the dog food into the cat food. Each day, mix a little more dog food in and take a little more cat food out.
Hopefully, that way, he will gradually adjust to eating dog food.
You can also try buying dry dog food and leaving it out for 48 hours. If he does not eat anything after 48 hours, mix a spoonful of cat food into the dry dog food.
He can go 2 days without eating. Often, people give up after 24 hours and feed the dog what they want.
The cat food is higher in protein because cats are carnivores and only eat meat. Dogs are omnivores and are suppose to eat meat and veggies. So the cat food can be difficult for the dog's kidneys to process over a long period of time.
I have researched the eating of horse manure because I have horses and my dogs think it is a good snack. So horse manure is high in calories. So, you want to limit the amount he eats. But it is not toxic to dogs. It can cause gastrointestinal upset and I am not a fan of cleaning up horse manure vomited by my dog. So keep that in mind too. In addition, you should deworm him every three months if he eats manure. You can buy liquid "pyrantel pamoate" over the counter. It is usually 1 cc per 5-10 pounds of dog by mouth. So deworm him every 3 months with the pyrantel pamoate.
I hope this helps.
If you have additional questions, please reply.