|Blood analysis is a useful tool in the diagnosis of clinical disease but should never be considered as providing a definitive opinion except where specific findings amount to irrefutable proof. For example, a positive finding of cancerous cells has to be seen as significant, but most results are not as black-and-white as that.
Where a horse is not performing well, one of the first causes to eliminate is infection and blood tests are effective in detecting signs of significant bacterial infection, though less so when it comes to viruses. The most important element in diagnosing infection rests with the white blood cells and interpretation of these will be made by your vet in conjunction with a laboratory.
If there is no infection, conditions like anaemia, dehydration and nutritional deficiency may be important and it has to be appreciated that, for top-class performance, blood readings have to be far closer to perfection than is the case with sedentary animals. In other words, a relatively low red blood cell or haemoglobin figure may mean nothing in a horse at grass, but failure to race, say, could easily occur where enough oxygen wasn't getting to the tissues for the same reason.
More to the point, we know that mineral deficiencies occur on particular soils, so that a copper deficiency, for example, might occur and cause serious problems for horses in full work. The blood picture may be considered to be within normal limits but the horse may tremble after work and display cardiac irregularities which are potentially dangerous. Supplementation will solve the problem, though it has to be precise and over-dosage can create more trouble.
The important blood parameters still relate to:
- 1) Oxygen carrying capacity. The total red blood cell count is important; remember that two horses of equal ability will not perform equally if one is short of oxygen for whatever reason. This applies equally for jumping or galloping, though the greater the demand the greater will be the gap between them on either count. Haemoglobin level is significant in this and needs to reach an ideal figure for performance. Don't be advised otherwise.
- 2) Packed cell volume is an indicator of the fluid levels, or the state of hydration. While a low PCV may indicate a shortage of RBC's, a rise can indicate dehydration, which means a thickening of the blood and more work for the heart in circulating it.
- 3) Even low grade infection can be very limiting in horses trying to compete and the likely effect is proportional to the demands of the work, inevitably worse for a racehorse than an eventer and so down the scale of demand.
- 4) Conditions like tying-up are complex and often an expression of clinical changes within the body. They can be an expression of deficiency, of errors in feed constituent levels, or of abnormality within the body - for example, liver disease. Blood enzyme tests can help to resolve the problem but are best discussed with your vet because of their complexity.