There are a lot of different possibilities for what may be going on with your Dane. The ones that I would be considering if he came to see me are:
1. One of the things that I think of first in a young 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 sometimes 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:
If I examined your Dane 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. 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:
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:
5. It does not sound likely because you don't see any abdominal distension, but in a Dane, I always have Gastric Dilatation and Volvulus (GDV, Bloat) in the back of my mind.
With this problem, a dog's stomach fills with gas which can happen after eating a meal, but then the stomach twists over on itself. The food that is trapped in there continues to ferment, more gas is produced, and it expands like a balloon. The twist in the stomach cuts off blood supply to the stomach, and to other internal organs. This is a true medical emergency! It is fatal without aggressive treatment.
Here is more about it:
GDV happens most often in deep-chested dogs like Danes, and Dobermans, and Shepherds. It is a true medical emergency! With this problem, dogs often have distended, hard, drum-like bellies from the swelling of the stomach as it fills with gas that cannot get out. Without immediate treatment it is almost always fatal.
The bottom line 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 much fluid your Dane is losing from both ends, I would strongly recommend that you take him in TONIGHT to see your vet. There may be something going on that needs immediate attention, and I don't like the fact that he is unable to keep water down now. He is going to become seriously dehydrated.
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. So, water is fine, but also he can have pedialyte, Gatorade, apple juice diluted 50:50 with water, or chicken or beef broth diluted 50:50 with water. Give the fluids in small amounts frequently. For a dog this size that means about 1/2cup every half hour.
3. After 12 hours, 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 Dane continues to vomit, develops blood in the stool, is lethargic or shows signs of abdominal pain, please contact a veterinarian immediately!
I really do feel that if he cannot keep down water, he needs to see a vet tonight! Good luck with your Dane!