In terms of what may be causing him to vomit... there are lots of different possibilities for what may be going on with your dog. The ones that I would be considering if he were on his way in to see me are:
1. One of the things that I think of first in a dog is that he may have a Gastrointestinal Foreign Body.
Dogs eat the strangest things - plastic bags, children's toys, bones, bits of towel, socks, rocks and other things. Often, these foreign bodies pass through the intestinal tract, but sometimes they do not. They may get caught in the stomach or the small intestines. The symptoms of a GI foreign body are generally vomiting, loss of appetite, depression and dehydration. If your dog consumed an object that is caught in the stomach or small intestines, it might explain the symptoms that you are seeing. This would be particulary true if the object were something like a ball that could bob over pylorus (outflow from the stomach) and then move away again. Thus, water could pass through but not food. In the case of an obstruction, surgery is often needed to remove the foreign object. I will include further information about GI foreign bodies: http://www.michvet.com/library/surgery_gi_foreign_body.asp http://www.petplace.com/dogs/gastrointestinal-foreign-body-in-dogs/page1.aspx If I examined your boy and was concerned about a foreign body, I would probably recommend x-rays to see if a foreign object were visible. A rock would show up very well on x-rays. A plastic bag would not show up on x-rays. It does, however, show up very well if the dog is given some barium (a type of milkshake like drink) by mouth. Then a determination can be made about how best to get this out of the dog, or whether it might move through on its own.
2. It is possible your dog simply has gastroenteritis from eating something he shouldn't have.
This is particularly likely since you mentioned he has a sensitive stomach.
Table scraps or twigs and leaves could be the culprit! Gastroenteritis is an inflammation of the stomach and intestines and can be caused by a large number of things, including sudden dietary changes.
3. A bacterial infection: Dogs can be affected by overgrowths of bacteria in the intestines. In an adult dog these might not be more than a nuisance. The 3 most common are Campylobacter, Salmonella and E.Coli. Here is a link with more information: http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=2232
4. Pancreatitis: This is an inflammation of the pancreas, often triggered by a high fat meal. With "acute pancreatitis" dogs are very sick, with severe vomiting, painful belly and fever. However, with a low-grade, chronic fulminant pancreatitis it is basically a "slow burn" version of acute pancreatitis. The pancreas remains inflamed, with periods of pain and nausea, and vomiting intermittently. Pancreatitis is a serious medical problem and is diagnosed by having bloodwork done and possibly x-rays. Dogs with pancreatitis may need to go on a course of antibiotics to treat the chronic pancreatitis and may need a prescription food to "put out the fire" of this chronic problem. Typically the diet is ultra-low fat. At first dogs may not want to eat it because of feeling nauseated and it does not tempt her. But with medications they soon feel *much* better and keep feeling well if they stays on an appropriate food. For more information: http://www.judithstock.com/Speaking_of_Animals/Pancreatitis_in_Dogs/pancreatitis_in_dogs.html http://www.peteducation.com/article.cfm?cls=2&cat=1580&articleid=335 http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=2214
The botXXXXX XXXXXne is that there are a number of possibilities for what may be going on. Your vet would need to do a physical exam and possibly some diagnostic tests to figure out what the underlying problem is. I would start with a fecal sample, blood test and abdominal x-rays. It sounds like it is time to find out what is going on!
Given how relentless your boy's vomiting is, I would strongly recommend that you take him in TODAY to see your vet. There may be something going on that needs immediate attention. If he were my patient, I would do a thorough physical, and maybe take a blood sample and some abdominal x-rays.
If he is feeling unwell at the moment, there are some things you can do at home until you can get him in to the vet:
1. WITH-HOLD FOOD for 12 hours since he has been vomiting today. This gives the intestines a chance to rest and heal.
2. When he is fasting, he can have lots of clear fluids, but only once it has been OVER 4 hours since he last vomited! Until then, remove all food and water.
So, once he stops vomiting water is fine, but also he can have pedialyte, Gatorade, apple juice diluted 50:50 with water, or onion- free chicken or beef broth diluted 50:50 with water. Give the fluids in small amounts frequently. For a dog this size that means about 1 cup an hour.
3. After 12 hours of no vomiting, you can start your dog back on a bland diet.
For patients that I see, I recommend a mixture of 75% cooked white rice, and 25% low fat protein. For the protein you could use extra lean ground beef, boiled with the fat scooped off, or chicken breast boiled with fat scooped off or even scrambled egg cooked without fat in the microwave. Feed small frequent meals. For a dog this size, I would suggest 1/2 cup every 3 to 4 hours.
4. After 1-2 days on the rice mix, you would gradually change your dog back to the normal dog food.
So, on day 3, give the rice mixture, but bigger meals, spaced further apart. On day 4, mix a little tiny bit of the normal food in there, and decrease the frequency so it is down to 3 meals or so. And so on.
5. Keep your dog as quiet as possible - just out to relieve himself and back in.
If your Lab continues to vomit, develops blood in the stool, is lethargic or shows signs of abdominal pain, please contact a veterinarian promptly. Good luck with your boy!
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.