I just adopted an 8 year old English Mastiff who was severely abused and starved. The shelter managed to get him to gain over 25 lbs (from 52 up to 75 lbs) in a month, but he can stand to gain another 25-30 lbs. Since we took him home a few days ago he has been resistant to eating. I have tried two different types of dog food and also tried adding rice. He will eat only about 1 1/2 cups a day. I am afraid of him losing weight again. Any suggestions?