Anaemia (a reduced number of red blood cells in the blood) is probably the most common problem affecting the blood in pets. In the early stages, there may be few symptoms of anaemia and these may not be easy to recognise. This is particularly true if anaemia develops very gradually because the body has time to adapt to the reduction in red blood cells. The first sign of anaemia may be low energy levels and general weakness due to reduced oxygen supply to the muscles. Anaemic animals often have a poor appetite. In severe cases more dramatic signs such as collapse and rapid breathing may be seen. If you look at the gums of an anaemic animal you will notice that they are pale or even white. Anaemia is not a disease but a symptom of another disease. Anaemia can be caused by loss of red blood cells through bleeding, a reduced production of red cells or destruction of red cells within the body (usually an immune mediated disease). If your pet is anaemic your vet will need to do some tests to find out what the underlying cause might be.
Bleeding or haemorrhage is something that almost all owners will have to deal with at some point in their pet's lives. This can occur as a consequence of a serious injury and may be obvious to the owner, eg a cut pad. However blood loss can also occur internally and this can be very substantial before signs are noticed. Sometimes the signs of bleeding will be related to loss of volume of blood or anaemia - lethargy, collapse and breathing difficulties. However, if an animal is bleeding internally signs may be related to compromise of other organs, eg coughing or vomiting of blood. All these situations need urgent veterinary attention.
Occasionally animals suffer a defect of the blood clotting mechanism. If the blood does not clot, even minor injuries (which might otherwise go un-noticed) fail to stop bleeding and become significant problems. If you notice bruising on your pet's skin or your pet suffers bleeding around the gums or nosebleeds then you should get advice from your vet. Some bleeding disorders are inherited, whilst others can be the result of liver disease or from eating rat poison. Whatever the cause it is important to get help quickly from your vet.