Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian. I am sorry to see that you have been waiting quite a while for an answer. I believe that your question was posted late at night when few veterinarians were available to answer. If you still need advice I'd like to try and help Seamus.
Given how quickly he became symptomatic I would be concerned that Seamus has one or more liver cysts that were ruptured secondary to the trauma suffered playing with his XXXXX XXXXX buddy. That would explain the serous fluid in his abdomen, enlarged liver with mildly elevated liver enzymes and his low globulin levels and increased white blood cell count.
Liver cysts are fluid filled cysts on the liver that tend to grow slowly and are usually benign. They can be present from birth or develop later. They don't usually interfere with liver function much as the rest of the liver takes over, and if there is a single cyst removal is curative.
If the cyst ruptures then fluid can fill the abdomen and the dog can become shocky due to changes in abdominal pressure on his other organs. I highly recommend that your fellow see a veterinary internal medicine specialist or board certified surgeon as soon as possible. I believe that he needs surgery to explore his abdomen and remove the leaking cyst.
Please let me know if you have any further questions.
Many thanks for your response. Approximately 4 years ago,whilst being scanned for another ailment,I was informed of the presence of various liver cysts.As you mentioned in your answer they appeared to be benign,but I was totally unaware of the possibility of rupturing,and to have such an energetic fellow as he was,the chances were high of such an outcome.To this end I believe you have confirmed my fears of the cause of this tragedy.We had the fluid drained from his abdomen (1 and 1/2 litres )and re-scanned by another vet,this confirmed a large anomaly present on the liver.As I could feel this shape easily with the fluid drained and am convinced that no such growth was present prior to this situation,I can only agree with your suspicions.We had Seamus put to sleep yesterday evening.Thankyou for your assistance at this sad time.