Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 16 years of experience. I look forward to working with you.
I am so sorry to hear Zip is experiencing this. Great job trying a special diet but with this level of weight loss I am afraid this is probably not diet related. Good to know the lab work (I assume you refer to a CBC, chemistry profile, urinalysis, thyroid check and stool check) was normal and radiographs (X-rays) looked good. But this is not going to be the end of looking for what is going on. If not already tried, a therapeutic trial with good anti-vomting medication would be a good step (such as Cerenia) to see if this stops the vomiting. IF not, then this gives us a lot of information and encourages us to focus on the upper digestive tract.
For next steps of testing, we need to look at the stomach/intestines to know if there is something going on like a tumor which cannot be seen on radiographs, or ulcerations, or or inflammatory bowel disease, or atypical infection, which may best be done via endoscopy. Or, you could start with an abdominal ultrasound with a very experienced clinician to look at the digestive tract and all organs. Also screening for chronic pancreatiits, if not already done, may be a good idea.
I am at a point I need to know what questions you have. I hope that the information I provided has been helpful.
Please let me know if for any reason you need further clarification, have more questions, or were expecting a different type of answer.
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