A “blood reading” or “blood picture” is a term often used by trainers when assessing the well-being of a horse in the build up to a race.

However, there have not been many articles written in laymen’s terms which explain what this means.

Each trainer has his own methods.

Some will regard blood readings as an important part of a horse’s preparation, others place less importance in it and others don’t do them at all.

A “heart rate” is another measurement which can be taken but this is not a common practice.

The Paul Lafferty yard use blood readings extensively and some of the information below was gleaned from an interview with his assistant trainer Roy Waugh.

The information about the Heart rates is courtesy of three-times national Champion trainer Sean Tarry, who often uses this training aid. 

Athletic performance in thoroughbreds, as in humans, is interlinked with oxygen supply.

Haemoglobin, an iron-containing protein within the red blood cell, carries oxygen to the rest of the body and the more haemoglobin present the more that can be carried.

Red blood cells and haemoglobin thus go hand-in-hand. 

Red blood cells and accompanying haemoglobin are created by bone marrow and the levels are raised through exercise.

The aim of training is to stress the system, so that bone marrow makes more red blood cells/haemoglobin for the workload.

Short, sharp work is the best way to increase red blood cell/haemoglobin levels.

There are two important measurements to be taken in assessing the efficiency of oxygen transportation in a horse’s blood, the haemoglobin levels and haematocrit. The latter is also known as the Packed Cell Volume (PCV).

The amount of haemoglobin in whole blood is expressed in grams per decilitre (g/dl). The normal haemoglobin level for horses at rest is 8-19 g/dl.

The haematocrit or PCV measures the percentage of red blood cells in blood. A normal PCV reading for horses at rest is between 32-48%. Lower than 30% may indicate anaemia. When the blood sample is taken it is separated into three parts, red blood cells, plasma and buffy coat. The buffy coat is essentially the layer between blood cells and plasma that contains most of the white blood cells and platelets. An abnormally high white blood cell count indicates an infection. 

When the number of red blood cells is too large there is a traffic jam effect and blood flow is restricted.

This is termed haemo-concentrating and is chiefly associated with intact males.

Gelding is the usual solution. Long, slow work can also help.

Haemo-concentration is an unknown term in most racing countries, but is well-known in South Africa. The reason for this is likely due to South African trainers’ tendency to do short, fast work on heavy tracks, which can cause a rapid production of red blood cells/haemoglobin.

Trainers would ideally be looking for a haemoglobin level of from 13,5 to 15 for a horse at rest and a PCV reading from 40 to 43.

An important difference in the physiology of horses and humans is that a horse’s spleen holds approximately a third of its total red blood cells and these are held in reserve until mobilised through exercise, stress and excitement. This is a common physiological design in flight animals, who require a sudden burst of energy to escape from predators. It also explains why a good temperament is so vital in racehorses. Those who get worked up before the race or during the running are releasing some of their splenic blood and wasting their oxygen reserves. However, those who are able to relax until asked for an effort in the straight will still have oxygen in the tank in the final stages and this often makes the difference between victory and defeat.

The horse’s physiology is also one of the reasons a measurement of red blood cell/haemoglobin content in horses at rest can’t always be exact as even the anticipation of the needle can cause excitement and the consequent release of the splenic blood. 

Therefore, the Paul Lafferty yard take the measurement after fast work at which stage the splenic blood will still be in the system.

However, the expected levels will then change.

A good reading for haemoglobin after fast work would be from 23 to 24,5 and a good reading for PCV would be from 72 to 75.

These readings can be a valuable aid to trainers.

If the levels are too low a couple of days before a race, the horse will have no chance and might as well be scratched. However, if there is still two or three weeks to the race the levels can be raised by short, sharp work.

The levels become more important as an indicator the longer the race is.

They become an even more important indicator in races run at altitude (e.g. Johannesburg), where the air is thinner.

The Sean Tarry yard take heart rate readings after grass gallops. A profile of a horse’s heart rate and recovery rate is created over a period of time. When a race is approaching the heart rate and recovery rate readings are compared to the markers on the profile and an assessment is made.

By David Thiselton