Anaemia may be caused by nutritional problems, for example iron deficiency or deficiency of vitamin B12, and can be remedied by supplementation. It can be caused by worm burdens, infections or by incidental blood loss. Parasites such as liver fluke cause anaemia, though the source of the problem may be difficult to pinpoint and speculative treatment with a suitable flukicide may be the best way of getting a result. Horses in cold stabling sometimes suffer low blood counts that reverse when they are moved into warmer conditions.

Horses are anaemic when short of red blood cells (RBC's) or have inadequate haemoglobin within them. The condition is marked by pale membranes and, if blood is analysed, the levels for RBC's and/or haemoglobin will be subnormal. It has to be understood in making a judgment that low readings may have little meaning for the sedentary animal; the performing animal that is most inhibited when blood levels fall below a satisfactory level.

The purpose of the RBC's is to transport oxygen to the tissues from the lungs and to return carbon dioxide for elimination from the body.

Inevitably, if there isn't enough oxygen the animal can't perform. Tissue functions, like muscle contraction, can't operate normally. The heart is placed under an abnormal burden trying to compensate. There is fatigue, weakness and considerable danger, if the condition isn't identified, of causing damage to the heart.

The first requirement is to look at the horse and the environment and consider if this may play a part. Worm infestations need addressing; deficiencies have to be identified, through laboratory assistance, and corrected. Mild anaemia is helped by providing haematinics, like iron and B12, available from a variety of sources today. Other specific deficiencies, like copper, need to be identified and treated with veterinary help. More severe and unidentified types will need full investigation before they can be treated.