While it is not uncommon for a Boxer dog to be skinny for anywhere from 2 to 10 months while he is transitioning from puppy to adult, it will be important to rule out any possible health issues before you take a few steps - and have some patience- for him to gain a bit of healthy weight.
Possible health conditions include but are not limited to:
• Thyroid issues
• Parasites (worms)
• Inflammatory bowel disease
• Disease of the pancreas
• Liver or gall bladder disease
• Heart conditions
• Liver problems
• Kidney disease
• Addison’s disease
• Diabetes
• Immune system problems
The Boxer should have a complete physical along with stool and blood testing. Also, even if your dog has recently been to the veterinarian, you'll want to have your Boxer examined if he/she seems too skinny and additionally has any of the following issues:
• Moderate to severe loss of appetite (Boxers that are a bit too skinny simply due to the normal growth stage will eat as normal- or just a tad
less - as the body temporarily stalls before filling out)
• Vomiting, dry heaving
• Diarrhea or any changes in stools
• Changes in mood or energy level