How to help my underweight dog gain weight after stomach issues?

If Diesel has food sensitivities (usually z/d is to address this) but still isn't gaining weight on it, I'd definitely let his regular veterinarian know that he still isn't gaining. Your vet may recommend upping his current food for more caloric intake, or recommend adding in some supplements such as rice or chicken that are gentle on the stomach still (unless he is allergic to one of those ingredients.) I'd hesitate to just add in any OTC food as that may interfere with whatever caused the initial inflammation and make symptoms worse. It would be best to monitor this with your vet so that you can track his progress and see if upping the amount of food helps, or if he continues to not gain weight. Most vets will allow you to walk in without an appointment for a weekly weigh-in.

I would recommend having her body condition score figured out first to determine if she is indeed underweight. Some pets are just leaner than others but are not considered to be underweight at all. https://www.google.com/search?client=safari&hl=en-us&ei=3essWYH8BcWXjwT5u4agBg&q=canine+body+condition+score&oq=aaha+body+condition+score&gs_l=mobile-gws-serp.1.0.0i71k1l5.0.0.0.53939.1.1.0.0.0.0.0.0..0.0....0...1..64.mobile-gws-serp..1.0.0.tM15jVEPrL8#imgrc=D5srd2kpWBMU1M: If she is considered to still be underweight then I would try to find out what is causing her weight loss and treating that directly. If there are loose stools then it's best to check her stools for intestinal parasites through your vet. If her stools are normal, then she may be going through a transient period of not gaining proper weight due to a previous illness. Increasing her current food amount can help. You can also try mixing in a high calorie puppy food for a few weeks. I wouldn't suggest this unless she is otherwise healthy and nothing else seems to help, because a consistent high calorie diet can do more harm (i.e. Pancreatitis) than good in some cases. Best of luck with your pet Layla.

Gentle feeding with a high quality, high calorie food such as royal canin gastrointestinal is very effective in regaining body weight and muscle mass. Ensure she is wormed regularly and monitor for any vomiting and diarrhea which may indicate bowel issues

I wouldn't recommend adding any additional food to help Simba bulk up - you should just increase the amount of puppy food that he gets each day. You could try increasing by about 25% for two weeks and then judge his body condition using this scoring chart to see if he seems like he is an appropriate weight. If your veterinarian recommended a specific diet for his diarrhea that he is still eating you should check with your veterinarian first to make sure it is okay to increase the amount of food offered or if there is something else he should be fed. Since he is feeling better he should gain weight quickly - don't forget to cut back on food again once he seems like he is back to an ideal weight. http://www.mabcr.org/template/upload_files/PuppyBodyCondChart.pdf

The first things to rule out would be gastrointestinal parasites, this is usually easy to test and treat. if this is not the case there are many gastrointestinal diseases that could cause that, each has different testing protocols, most have special foods that need to be tried. if he is not neutered, having him castrated can also help him gain some weight.

First, I would make sure you feed Dio a puppy food, not an adult food. Second, make sure you are feeding him enough cups of food. Third, make sure to feed a high quality large breed puppy food. A grain free brand like Merrick or Wellness or Taste of the Wild would be great. Even Science Diet Large Breed puppy would be ok. Last, make sure your puppy has had a fecal test run to make sure he doesn’t have worms. A monthly heartworm prevention, like Heartgard or Interceptor, treats parasites too. If your dog is still not gaining, they may need further testing or work up. In addition, adding a probiotic may help as well. I like Animal Essentials Plant Enzymes and Probiotics.

Provide food that is high in calories, like puppy food or a food that’s designed for active, athletic, or working dogs. Higher protein and fat pet foods are best. Underweight pets should be eating foods that are around 30% protein and 20% fat if they’re eating dry kibble; 7% protein and 5% fat (or higher) if you’re feeding a wet food. Intersperse your pet’s diet with small amounts of high-calorie supplemental canned food or canned products made of 100% meat sources. These will have a high protein and fat content, like 100% pheasant or bison, for example. They won’t say “complete and balanced” but rather “for intermittent or supplemental use” because they’re not meant to replace regular feeding. Some moist foods may be easier to digest, so your pet may retain more nutrients, and more importantly these products tend to be more palatable and tempting to a pet who isn’t eating enough. Any diet changes should be done gradually over a week's time as to not cause any GI upset. Hope this helps. Best wishes.