According to the Canine Manual of Infovet.com, vomiting is a common, classic symptom of gastrointestinal troubles in dogs. It may be caused by many things: a blockage of intestines, an empty stomach, ingestion of harmful substances, or harmful organisms such as viruses, worms and bacteria. It can be difficult and distressing to diagnose the cause of your dog's trouble, but it is well worth the effort.
Several things could be the cause of your dog vomiting strangely colored liquid. The least harmful cause is an empty stomach. If your dog heaves, but has nothing in his stomach, he will expel green bile, his stomach's natural digestive juices. Another possibility is your dog may have ingested something indigestible or irritating to her stomach. When the vomit is green, your dog may have eaten grass or, more distressingly, antifreeze. In addition, your dog may be suffering from an illness caused by bacteria, a virus, a parasite or even a disease like diabetes or cancer.
To prevent your dog from vomiting green liquid, make sure your dog is well-fed and hydrated. Keep antifreeze out of reach, even when bottled. According to Animalemergency.com, dogs may sometimes bite through anti-freeze caps and bottles just to get to the sweet-smelling liquid. Keep your dog away from spoiled foods, the garbage, or other potentially contaminated substances. This will lower her chances of catching a virus, being infected by harmful bacteria, or becoming the host of a pesky parasite. To further protect your dog, make she is vaccinated against deadly viruses, such as parvo and distemper.
It is very important to pay close attention to the manner in which your dog vomits; this may may clue you in to the seriousness and nature of his condition. If your pet regurgitates his food, this suggests a blockage in the upper digestive tract. If your dog is vomiting continuously, this usually implies simple stomach irritation. When your dog vomits after a coughing or hacking fit, this may mean your dog has respiratory problems.
Chronic vomiting, vomiting over a long period of time and accompanied by weight loss, poor appetite, and a general lack of energy my connote kidney and liver disease, diabetes, parasite infections or even cancer. In the case of projectile vomiting, your dog my suffer from a blockage in the digestive tract. In some cases, the green liquid may be mixed with fresh blood; this means your dog is bleeding somewhere inside his digestive system. In the rare occasion that your dog vomits stool, this should be treated as an absolute emergency, for your dog's lower intestines may be completely blocked. Also, if your dog vomiting in conjunction with neurological symptoms such as convulsions, the cause may be neurological and not gastrointestinal.
Until you can get your dog to a vet, put your pet on bland diet of chicken or lamb with white rice or baby food. This should settle her stomach. You can also try Pepcid AC--famotidine--an over-the-counter (OTC) drug for humans that can be found in most any drugstore.
If you suspect your dog has ingested something harmful or irritating, these situations may call for forcing your dog to vomit with a one to three teaspoons of hydrogen peroxide. This may save your dog's life, as you are encouraging his body to expel the harmful substance, but some poisons do more damage when vomited, so this solution should be approached with caution.
Your veterinarian will undergo a more involved inspection or your dog, and he will need both a stool sample and a few answers from you. Your veterinarian will want to know when your dog started vomiting, how often he vomits, the nature of the vomiting and how the relationship of the vomiting to your dog's meal times.
The stool sample will be tested for parasites, viruses, and bacteria such as Salmonella and Campylobater. She will also check the stool for blood. She will check your dog's mental condition, his temperature and she will check for any objects lodged in your dog's throat. She will check your dog's organs to rule out inflammation, abnormal growth, intestinal tears or excessive gas.