Onions can cause your dog to be ill due to thiosulphate poisoning. Dogs who have ingested onion can develop anemia due to red blood cells bursting. The first signs of onion poisoning are gastroenteritis with vomiting and diarrhea. There will be a loss of appetite and lethargy and trouble breathing. The breathing is caused by the fact that the red blood cells carrying oxygen through the body are reduced. Frequently their urine will be reddish.
The acute diarrhea and vomiting can lead to dehydration. You can check this by lifting the skin between your dog’s shoulder blades and if it stays tented or is slow to return to normal position, your dog is dehydrated and needs to be seen by your Vet so fluids can be given.
The poisoning occurs a couple of days after the onion has been digested. It does not matter if the onion was raw, cooked or mixed with other food. A single meal of 1 pound of onions can be dangerous to a 15 pound dog. The same poisoning can occur if smaller amounts were fed over several days. The condition does improve once the dog is prevented from eating more onions. If your dog’s gums are pale white and he develops symptoms of onion poisoning listed above or becomes dehydrated, contact your Vet.
A dietary indiscretion such as ingesting human foods including onions even if a toxic amount was not consumed, can still cause diarrhea and if the irritation continues there can be bleeding. If your dog is eating and drinking normally, Kaopectate at 1 teaspoon per 5 pound every 2 - 6 hours or Immodium at 1 mg per 15 pounds one or two times a day can be given for diarrhea. Canned pumpkin (not pie filling) will also absorb excess fluid in the bowel with just a spoonful added to the dog’s food. Some experts will recommend a bland diet for a few days of boiled chicken and rice.
The most common reason for blood in the stool is parasites such as worms or a protozoan infection such as coccidia or giardia. So if there is no improvement you will want to have this checked. The most common worms found in dogs are: Roundworms, Hookworms, Tapeworms, and Whipworms and Heartworms
In some cases these worms are passed from the mother to the puppy, in other cases such as tapeworms, they are contracted by other methods such as ingesting an infected flea. Most over the counter medicine will only kill one or two types of worms, so your best bet is to take a fecal sample to your vet to determine the type of worms your dog may have and then decide on treatment. Dogs should be checked for worms periodically even if they appear healthy. This is so if your pet does become ill, you are not fighting a worm infestation along with a more serious problem.
For additional information about worms, see this site
Common dewormers are Panacur, which is a prescription product so you need to obtain it from your Vet and it works on roundworms and whipworms. Wormers labeled as Pyrantel Pamoate are the best over the counter medication for roundworms. Drontal plus is also a prescription product and is used for the treatment of Tapeworms, though dewormers with praziquantel work well against tapeworms. Revolution and Interceptor as well as other heartworm medications also control whipworms and roundworms. Another reason to keep your dog on Heartworm medication.
Information on coccidia
Symptoms are diarrhea which could be mild or severe depending on how infected they are. If severe there may be blood and mucous along with vomiting, loss of appetite leading to dehydration.
Information on giardia
Symptoms of giardia are diarrhea with possible terrible smell, mucousy stool and sometimes bouts of vomiting.
Other causes could be anal growths, infected anal glands and inflammation within the large intestine. You can read about the various cause of red blood in the stool here:
I hope you find this information helpful.