Reactive dog— need advice on testing

Hello All

Background

My intact male dog is 4 years old. He is a Labrador/Pyrenees weighing about 80lb. He has had chronic GI issues as of July. He was exclusively an outdoor dog up until my husband and I moved and bought our own place. He is now indoors only and goes on 3 walks a day. He used to eat wet food/kibble/broth every day and as of July no longer wants the wet food or broth (doesn’t matter if it’s beef or chicken). Now, he will only take bites of the wet food but no longer likes it mixed in his food. His caloric intake varies per day. He will eat anything from 1500-1700 calories. There are days where he is very hungry. On an off day he will eat less.

In July, he began to vomit bile in the morning about once a week. This was worrisome so I took him to the vet and because of his reactivity we were unable to do further testing besides an evaluation. He was prescribed probiotics and antibiotics and were told the vomit in the morning may be due to an empty stomach so we began to feed him right before bed. He did well for a few weeks and then noticed his poop was a little orange and eventually did not want his kibble anymore. Since he was a puppy he was on Beneful so we never thought to change it but because or his refusal we now feed him Pro Purina Large Breed Chicken and Rice Formula. He did not like the sensitive stomach formula. Initially, he did very well and had no issues. His vomiting and orange poop subsided.

Fast forward to September, he began to have GI issues again. His poop was occasionally dark green. Or it was a healthy brown then ended with a bit of yellow. On rare occasions he had days where he didn’t want to eat. I am positive this is not due to rat poisoning because we have none at home. I also work from home and watch him everyday day/all day. I am also very vigilant on our walks. I also don’t believe this is an obstruction as he has pooped and peed and acts completely normal. I also took a stool sample to the vet where they did not see any signs of parasites or worms.

Normal stools have become less and less normal and almost always on the softer side. He has also began to eat less and less kibble. So we substitute the amount of kibble he was leaving for white rice and boiled chicken at night with supplements. I don’t know what else to do so he can eat his full meals. This worked and vomitting in the morning subsided again.

However, in November he began to vomit in the mornings again regardless of the same routine. It began from once a week to 3 times this week alone. We began Pepcid this week but he still vomited this morning. I’m just worried there is something much bigger that we need to address now.

Because of his reactivity, he needs to be sedated. He is very fearful and we work on this everyday with him. His visit in July was horrible he was so nervous and he’s a big guy so I also am very cautious of the vet staff. My plan is to take him this week and do the necessary testing while under sedation. He very rarely acts lethargic and it is only when his stomach is really really messed up and/or has liquid diarrhea. This is very rare. He does not show any other signs of allergy (licking paws, ear infections, etc). 95% of the time he wants to go on his walks and is very happy and shows his belly.

My question is— what testing would give me the best answer as to what is going on? I want to minimize the times we need to go in as I’m afraid this will back track any training we have done. I am planning on asking for a full blood panel with testing of pancreatitis. Is ultrasound better than X-ray for imaging of tumors? Should I ask for endoscopy now? Are there any other tests I’m not considering? TIA!