It may not be the most glamorous part of owning a pet. But keeping an eye on what comes out, in other words their urine and faeces, is an important part of monitoring your dog’s health. Changes can sometimes give an early indication that something may be amiss. A common concern for pet owners is an alteration in the colour of their pet’s stools. Normal dog poo should be a medium dark to pale brown colour. Various changes in colour might be noticed if there is a problem including very pale stools, dark red or even black stools, and not unusually a green discolouration.

If your pet’s poo turns green it can be useful to check whether there are any other signs of potential problems

Questions it may help to ask yourself include:

  • Is the poo a normal consistency – harder or softer than usual?
  • Has your pet eaten anything out of the ordinary?
  • Does your pet seem unwell in themselves?
  • Are they showing any other signs of illness?

If your pet seems unwell then it is important to consult with your vet at the earliest opportunity.

There are lots of reasons why faeces may take on a verdant hue

During the normal process of digestion, bile pigments are produced by the liver and get mixed with the contents of the intestine. Bile starts green in colour, but is broken down by intestinal bacteria and turns brown. In combination with the digested gut contents this produces the normal colour of faeces.

A very common source of green discolouration in stools is material containing blue or green pigment

When it is eaten, it then passes through the intestinal tract unchanged. Common culprits include grass or plant material, certain supplements and food colourings. Most of these are harmless. However there are some common poisons that can cause a blue or green discolouration of the faeces. These include slug pellets, and rodenticides or rat poison.  In most cases there will be other, more obvious signs that your pet had ingested a toxin before a change in stool colour becomes evident.  

Rat poison works in two possible ways. Some types affect the blood and prevent it from clotting. This causes signs such as unusual bleeding and bruising. Other types work by causing calcium levels in the blood to rise to toxic levels. This causes excessive thirst, lethargy and weakness, progressing to kidney failure. It is vital to be vigilant about what your pet ingests, as often by the time they are showing signs of illness, it can be very hard to successfully treat the poisoning.  

Slug pellets also contain a blue or green pigment that may be noted in the stools. Ingestion of this toxin can cause neurological signs such as tremors, seizures and a rapid increase in body temperature. Again rapid treatment is essential as a relatively small amount can be deadly. Pet friendly slug treatments are available and these should be used whenever possible.

The importance of transit time

If the intestinal contents move through the intestines more quickly than normal, the green bile pigments from the liver may not undergo the normal breakdown by the gut bacteria, and therefore may not change from green to brown. Green discolouration is therefore very common in combination with loose poo or diarrhoea; where intestinal contents move very quickly through the gut.  

Could it be due to an infection?

This is one reason that green stools can often be seen in pets that are suffering from infections of the gastrointestinal tract. One of the most common bugs to cause these changes is a parasite called Giardia. Giardia is a very hardy microorganism that can be found in the environment, where it can survive for many months before infecting an animal. Giardia infections are usually diagnosed on a faecal sample. If it is found your vet will prescribe a short course of medication to clear the infection. It is also really important to clean the environment. You may need to treat other dogs in the household to prevent reinfection.  

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Or another intestinal disturbance?

Other diseases of the intestines can also cause green poo, often accompanied by diarrhoea, mucous and sometimes even blood in the stools.  Common problems include food allergies, inflammatory bowel syndrome, and even sometimes a change in diet, especially if the new food has been introduced too quickly. In addition medications can affect the colour of a dog’s stool.  For example a course of antibiotics which alters the normal bacteria in the gut or a course of laxatives that speed up the movement of food through the intestines.

So if you notice a green hue affecting your pets poop firstly look to see if there is anything in their diet that might be causing the discolouration.  If there is no obvious cause for it and especially if your pet is showing signs of being unwell, or if you suspect they may have had access to toxins, it is essential to consult with your vet at the earliest opportunity to rule out serious problems and get any treatment that your pet needs.

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