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Lowered Alkali Reserve.

The pH of the blood is critical.

If you are looking for a reason why there is a sudden, and apparently inexplicable drop in your horse's racetrack performance ... read this bulletin!

The one single factor which causes a horse to "train off" faster than any other is a disturbance in its blood pH balance. Almost impossible to detect, especially in its early stages, this pH disturbance can be attributed to an excessive build up of acids in the horse's system, a depletion of its natural alkali reserves, injudicious training techniques; and other closely associated factors such as high grain diets, the prevailing climate and workload. A drop in the pH indicates an increase in the acidity of the blood.

In lay terms, this is referred to as acidosis, but more correctly it is the lowering of the alkali reserves.

The blood of the equine athlete has a very delicate acid/alkali balance. Optimum performance demands that this balance be maintained within very narrow, even critical, limits.

Definitions:

The pH of a solution is a symbol for the power of the hydrogen ions multiplied by 10.

An acid is a solution which provides hydrogen ions (H +) and can thus increase the H + of a solution, consequently lowering the pH - i.e. increase the activity.

A base is a substance which accepts hydrogen ions and can thus decrease the H + of a solution, consequently raising the pH - i.e. decreasing the acidity or raising the alkalinity.

The pH of the blood has to be maintained within extremely narrow ranges for optimum physiological functions. Wide variations, which are encountered in certain diseased states, are life-threatening.

Acidosis is a loose term which is applied to a lowered alkali reserve in the body. From the point of view of a horse in training, as opposed to the many pathological conditions that can result in acidosis, a Lowered alkali reserve is the direct result of strenuous muscular exercise.

Lactic Acid is an organic acid normally present in muscle tissue, produced by anaerobic (in the presence of inadequate oxygen) muscle metabolism; it consists of 2 parts positive hydrogen ion and a negative lactate ion. It is formed when the glycogen stored in the muscles is broken down and used for energy.

Analysis of 1,379 racehorse bloods confirms need for an alkali reserve replacer.
A unique and exhaustive study on the precise effects of work and climate on the body chemistry of a racehorse in training was conducted by Ranvet in 1986 at Sydney's Randwick Racecourse.

A total of 1,379 horses were involved in the study, one of the most comprehensive ever undertaken in Australia. A normal pH level was determined; the dramatic drop in base excess levels which were observed established the need for an alkali reserve replacer,, and recovery rates were monitored.

This study was undertaken by one of Australia's most eminent racehorse veterinarians who continued working on the project up until the beginning of 1992. A summary of his findings is set out in the tables below.

Blood Gas Analyses of Horses in Training.

Averages for pre and post work:

Summer and Winter

Table 1: Fast Work - Summer

H 2C03 = Carbonic Acid HCO 3 = Bicarbonate *The normal ratio = approximately 1/20 

NB: Summer heat and humidity tends to reduce this ratio i.e. a tendency towards acidosis.

Table 2: Fast Work - Winter

NB: Recovery times quicker in winter.

What is a normal pH?

The normal pH of a horse's blood is between 7.42 and 7.45, so you can see just how narrow the range is... "point 03 " of a decimal point in fact! Any reading below 7.40 is an indication of "acidosis" (see Table 1), while a reading of 7.20 would indicate severe "acidosis" (a severely depleted alkali reserve).

An explanation of what goes on.

Regardless of whether it is summer or winter, the end result of (a) converting grain to energy and (b) hard work and stress, is an abnormally high production of body acids in the horse's system.

Highly strung horses produce even greater amounts of body acids, as they expend more energy than the placid animal.

Lactic acid accumulates in the muscle when the supply of oxygen is insufficient for the oxidative processes and quickly diffuses out into the blood stream. In moderate exercise the rate of rise of lactic acid is greatest at the very start of exercise before the circulatory and respiratory systems have reached optimum output. This diminishes as a steady state develops.

The unfit horse and the horse coming into work fresh, or for the first time, produces greater quantities of lactic acid for a given workload. As the horse becomes fitter, his ability to buffer and cope with the acid produced improves quite considerably. Fillies also seem to be more prone to this condition than colts or geldings. The reasons for this are presumably hormonal, but as yet are not clearly understood.

In strenuous exercise, due to the relative deficiency of oxygen, the excessive accumulation of lactate ions represents a considerable acidosis with a marked lowering of bicarbonate concentration.

The body cannot stand acidosis for long and it has a very effective built-in system to counter it. Following exercise some lactic acid is converted back to glucose to be reused at a later time and in addition the bloodstream can "buffer" the acid.

The other compensating mechanisms are (1) increased respiration which lowers the carbon dioxide tension (pCO) and (2) increased excretion of hydrogen ions via the kidneys.

In exercise, a much greater quantity of lactic acid escapes in the urine. Such a process helps to minimise the production of acidosis, but it also represents a loss of base as well as energy producing substances.

Quite simply, buffers and buffer systems "mop up" the excess acid, neutralising it, but this is done at a cost and particularly where very considerable amounts of lactic acid are produced, the buffer system can be overtaxed, i.e. the cost is too high. A major part of the buffer system is bicarbonate, which combines with acid and carries it away. It can be seen that bicarbonate therefore is used up as that acid is neutralised and removed; that is the price, a loss of bicarbonate.

Adding excess bicarbonate is not the answer.

Before we go any further, it should be pointed out that too much supplementary bicarbonate can be bad for the horse. No more than 30g extra per day should be given.

The answer is not simply to supplement large amounts of extra bicarbonate, but rather to strengthen the buffer systems to allow them to cope better with the surges of lactic acid after races and workouts. 
This strengthening of the buffer systems can easily be done by adding Ranvet's Neutrolene or Ranvet's Neutrolene Plus to the feed on a daily basis.

Neutrolene is a citrate-based buffer system as is Neutrolene Plus which has the added refinement of another specialised buffer - both are highly effective in countering acidosis.

In summary:

The body's bicarbonate supply is used up and the body's natural buffer systems are stretched to their utmost in the racehorse in work. Acidosis may be more correctly called depleted base (alkali) reserve. The bicarbonate and other buffer systems have a reduced ability to neutralise the acids - remember that bases (alkalis) are required to balance acids.

Remember that acidosis may not be the classical "tying-up" so familiar to most trainers; rather it may show up as a poor finish, the horse going sour, or the loss of the will to win.

Tying up (muscle tension/spasm) involves chronic tension in the muscles due to overwork. When the muscles are active, they produce lactate as part of their normal metabolism. Too much lactate causes lactic acidosis, a lowering of the pH in the muscles and the body in general. This impacts the efficiency of metabolism, giving rise to fatigue. The excess lactate prevents the muscles from relaxing properly following contraction. As a result, large muscle groups tend to seize up, remaining in a state of contraction.

In mild tying up, the horse’s muscles are extremely sore and stiff. In full blown tying up, the horse is unable to move.

The areas typically affected by tying up include the horse's neck, back, shoulders, zones of previous trauma and areas where other muscles have attempted to compensate for those already affected.

Prolonged muscle fatigue can, in time, affect the skeletal, circulatory and respiratory systems.

Daily supplementation with either will bolster the body buffer system, allowing it to cope more successfully with "acidosis" by adding to the alkali reserve.

Do you need to know more about what makes a horse perform better? Contact Ranvet

This technical note is just one of many produced by Ranvet Pty. Ltd.