One of the challenges when writing this column is the fact that this is a family newspaper that people may be reading over breakfast, lunch or dinner.
The veterinary world includes aspects of life that are unsavoury: illness involves messy secretions, strong odours and other unpleasant realities. I try to avoid writing anything too graphic, to avoid causing upset.
That said, this week I am discussing a problem that is, by its nature, unpleasant. I'm talking about the common problem of blood being passed in the faeces. This is a common issue, and I suspect that many readers may want to know what to do if this happens to their dog or cat. Read on to find out but please finish eating before you do so.
I've always thought that it's one of evolution's clever ideas to make blood a bright red colour. This makes it very noticeable, to the extent that it is difficult to miss it. If blood was grey, brown or even black, it might not be noticed. But if your pet passes fresh blood from their rear end, the red colour draws attention to itself.
In fact, blood from the rear end is not always bright red when it comes out: the colour depends on the site of bleeding.
The digestive tract is divided into four main areas: the stomach, the small intestines, the large intestines, and the back passage. If there is active bleeding from the large intestines or the back passage, then the blood is likely to be the same red colour as fresh blood. This is known as "haematochezia"
If, however, the bleeding is from the stomach or small intestines, then while it will be red at the point of bleeding, the fresh blood will be digested as it passes through the digestive tract, so that by the time it emerges from the rear end, it's likely to be dark brown or even black in colour. The original red colour is often present to some extent, perhaps only noticeable as the droppings are cleaned up, but some people may miss this. If there's a significant amount of digested blood, there's often a distinctive strong smell too. When there is this type of digested blood in the faeces, it's known as "melaena".
There are many possible causes of blood in the faeces, whether from the lower digestive tract (fresh) or the upper digestive tract (digested). However, regardless of the cause, there is a basic principle that's involved. Blood is meant to stay inside blood vessels: by definition, bleeding occurs when blood escapes from those blood vessels. So when blood is seen in the faeces, this means that the blood vessels lining the digestive tract have been disrupted or damaged.
The most common cause, in dogs at least, is severe gastro-enteritis. This is a common condition, caused most commonly by dogs' predilection for scavenging. The sequence of events is as follows: the dog finds something unsavoury while out on a walk (rotting vegetation, half-chewed bones; the list is endless). The dog scoffs this before their owner can stop them, and now their digestive system has to cope. Often, the unsavoury item causes irritation: if the lining of the stomach is irritated, the dog may vomit immediately. If the substance passes beyond the stomach, the irritation to the intestines causes a different problem: diarrhoea. In many cases, the dog may suffer from that classic combination: vomiting and diarrhoea.
In most cases, a simple approach to this problem is all that's needed. As long as the dog remains bright and cheerful, it's safe for owners to fast their pets for twelve hours, then give a bland, easily-digestible food for another 24 hours (e.g. chicken and boiled rice).
If you could see the lining of the stomach and intestines in these mild cases, it would look red and sore, just as your skin would appear red and sore if you rubbed your forearm with a fingernail for half a minute. Whether it's the intestines or your skin, as long as the original cause stops (the foodstuff is ejected, or you stop rubbing your forearm), mild inflammation like this soon resolves.
It's very different when the irritation is severe enough to cause bleeding. To use the same analogy, this is similar to the situation that would follow if you continued to rub your forearm with a fingernail for five minutes. Eventually, the surface of the skin would be damaged, and you would damage some of the blood vessels below the surface. Your skin would start to ooze blood. This is precisely what happens when a dog eats something highly irritant: the surface of the stomach or the intestines starts to ooze blood, and subsequently, blood may be seen in the faeces.
This is far more serious than a mild irritation: the barrier between the outside and the inside of the body has been breached, and there is a risk that bacteria may enter the body, with serious consequences. For this reason, whenever blood (fresh or digested) is seen in the faeces, a pet needs to be taken to the vet. A full assessment is needed, and sometimes antibiotics may be prescribed: this is a decision that the vet will make. Other times intravenous fluids are necessary, due to the severe dehydration that often happens at the same time.
There are many other causes of blood in the faeces, from viruses to poisoning to tumours, but the recommended action in all cases is the same. If your pet passes blood, you really do need to take them to the vet.