EQUINE ANEMIA IS ONE OF THE MOST COMMONLY MISDIAGNOSED HEALTH PROBLEMS IN HORSES. WHILE IT CAN BE DIAGNOSED SIMPLY BY TAKING A BLOOD SAMPLE, drawing the blood is where the simplicity of this process ends. What is anemia? Most define it as a below ‘normal’ count of red blood cells in the blood. The Merck Veterinary Manual provides a more scientific definition: “Anemia is a condition characterized by insufficient circulating hemoglobin (Hgb). It results from excessive red blood cell (RBC) destruction, RBC loss, or decreased RBC production. Anemia is a manifestation of an underlying disease process, therefore, the response to treatment of an anemia is transient unless the underlying disease process is addressed.”
What is normal? Is normal the same for a foal, a broodmare and a racehorse? Normal is a statistical term. The best normal range comes from previous data on the horse you are measuring under his normal, or better yet, his optimal health conditions. Normal ranges will vary between laboratories and other variables such as the age, sex, breed and management of the horse. Horses of ‘hot-blooded’ descent (Thoroughbred) tend to have higher values for RBC, Hgb and packed cell volume (PCV) than ‘cold-blooded’ (Draft) or mixed-blooded (Warmblood) horses.
A single occasion blood evaluation will indicate whether there are obvious abnormalities, and only useful with a thorough clinical evaluation. It is much easier to identify when something is abnormal or when you can expect poor performance, than to identify when the situation is optimal or when the horse is in its best shape.
While there are many causes of anemia, they can be grouped into three main circumstances. A horse may become anemic when production by the bone marrow fails to keep pace with demand (hypoproliferative anemias), loss of blood from the body (hemorrhage), and finally destruction of RBC (hemolysis). Since new RBC are produced at the same rate as old ones are removed, most incidences of anemia are caused by chronic disease, or a traumatic event involving significant blood loss.
Anemia caused by significant external bleeding is the easiest to identify. Other causes of anemia, those caused by disease states, are considerably more difficult to diagnose. Any prolonged internal bleeding can cause anemia. In addition, parasitic infestation, ingestion of Red Maple leaves, renal disease, Equine Infectious Anemia (EIA), gastric ulcers, chronic inflammation and pneumonia are just some of the disease states that may cause anemia. What clinical signs would indicate to a horse owner that their horse might be dealing with anemia? Some of the most common signs are: depression, decrease in appetite, fatigue or reduced stamina, loss of condition, elevated heart rate, pale or white mucous membranes, yellowing of the eyes, discoloured urine, and/or trauma that causes excessive bleeding. Aside from having a horse that has had an incident involving serious bleeding, the other signs of anemia are pretty ambiguous. Fatigue, loss of condition and/or appetite and depression are all signs that point to a myriad of equine health issues.
What should a horse owner do if they suspect that their horse is anemic? Call a vet. A blood sample is the only way to diagnose anemia in the horse. This is done through an analysis of the PCV. Blood is composed of plasma and cells. Plasma is the liquid part of the blood and is 90% water. There are four types of cells: red, platelets, lymphocytes, and phagocytes. Lymphocytes and phagocytes comprise white blood cells and are responsible for immunity and fighting foreign bodies. Platelets are involved in clotting the blood and red blood cells contain Hgb, which carries oxygen to all the tissues of the body.
The PCV will tell the veterinarian what the percentage of RBC is in the blood. When settled in the collection tube, the blood forms three distinct layers: red cells, white cells, and plasma. While this method of analysis sounds straightforward, there is a twist.
The results of the PCV can be complicated by the condition of splenic contraction. Splenic contraction is a function that is unique to very few species (not found in humans), and explains one of the reasons a horse is such a superb athlete. Contraction of the spleen substantially increases the PCV, Hgb and RBC during exercise or excitement. Increases of 41, 39 and 50% for RBC, Hgb, and PCV, respectively, have been reported in horses after a short, intense exercise period. It is important to note that horses are capable of storing 30% (and maybe up to 50%) of its total RBC in their spleen. A typical racehorse has a circulating blood volume of approximately 50 L, of which 20 L (40% PCV) are circulating RBC while the horse is at rest. A further 10 L of RBC (50% more) are waiting in the spleen for a moments notice. Essentially, the horse is able to blooddope itself every time it is excited or moves from the jog into a gallop. A resting PCV, therefore, indicates a lower percentage than the total number of RBC actually available. On the other hand, following a period of exercise or excitement, the PCV will be elevated above its normal range. Consequently, PCV must be evaluated giving consideration to the probability of the results being an indication of a horse’s excitement level as much as an indicator of anemia. It is important to collect samples with a minimum of resistance and excitement to minimize the degree of splenic contraction.
Dehydration and fitness level also impacts the evaluation of the PCV results. It has been established that as an equine athlete trains and becomes increasingly fit, the volume of their RBC increases.
Evaluation of the PCV is based on a ‘normal’ PCV range of 31-47%. A horse with a PCV of 30% is considered anemic and, if the PCV drops below 15%, the horse may require a blood transfusion. Galloping exercise has the ability to raise the PCV as high as 65-70%. Now that the composition of the blood and the assessment of screening tests, including the complexities of splenic contraction have been introduced, it is time to look at the role of nutrition in the maintenance of healthy blood cells.
Nutritionally induced anemia, specifically, iron deficiency, is extremely rare in the horse.
At this time, it would be prudent to emphasize that anemia is not the same as iron deficiency. A true dietary iron deficiency has yet to be scientifically detected in horses under normal feeding practices. The reason being that the average horse only needs 40 to 50 mg of iron per kg of its feed. Most forage will range from 100 to over 300 mg/kg of iron. Oats contain 65 to 95 mg/kg and most commercial horse feeds will contain over 150 mg/kg. Consequently, it is mathematically impossible not to provide an adequate amount of iron. In a rare case, when it seems likely that an iron deficiency exists, measuring serum ferritin concentration is a better assessment of iron status than measuring PCV. Additionally, there are no scientific papers in the literature documenting enhanced Hgb or oxygen-carrying capacity of RBC with the use of iron supplementation in horses under a typical feeding program. On the other hand, there are papers detailing the toxic effects of excess iron.
The caution here is that iron toxicity is more dangerous and prevalent to a horse than iron deficiency. Unfortunately, the signs of iron toxicity can often be mistaken with those of iron deficiency. Iron is stored in the liver and spleen with no means of discarding the excess iron. The excess accumulation can grow to such proportions that liver damage occurs. High levels of iron will also have an antagonistic interaction with copper, manganese and zinc and can provoke a deficiency in these minerals.
Notwithstanding, horsemen, bound to tradition, are blindly spending money on iron supplements to treat “anemia” in racehorses. Informed trainers understand that anemia in racehorses is rare and if it did occur, through hemorrhaging for example, it would not be advantageous to treat with iron.
Production of RBC is dependent on a hormone (erythropoietin [EPO]) and an adequate supply of essential nutrients (EPO is a banned substance in competition and is another article in itself). These essential nutrients include iron, copper, vitamin B12, and folic acid (another type of B-vitamin). Deficiencies in any of these can impair RBC production as these nutrients all play an important part in the synthesis of Hgb, the special protein that carries oxygen in the blood. Under stressful conditions, such as high-intensity exercise, there is a greater probability of a vitamin B12 and folic acid deficiency than an iron deficiency.
If a horse becomes anemic, there are a few things that the horse owner should know in order to plan and carry-out a suitable treatment program. The first step in combating anemia is managing or better yet eliminating the cause of the condition. The next step would be to re-visit one’s feeding regime. This involves an analysis of the hay that is currently being fed. Of note: no two harvests of hay are alike, one cannot assume that a different cut off of the same field will contain the same nutritional values as the last. Vitamin availability in hay should be considered as zero as the quantities of vitamins available are in steady decline to the point where they are negligible, at approximately six months to one year after harvest. Horse owners must test each lot of hay and, in conjunction with the nutritional information on the concentrates being fed, and preferably an equine nutritionist, balance rations for each of their horses based on individual need. The balance of vitamins and minerals is the key. Interactions must be managed and overdosing avoided.
Achievement of balanced, individualized, rations is the absolute basic building block on which to construct a happy, healthy, equine companion. As we have assumed DePaulo who seems to always have a few stakes horses in his barn. This year Bad Hat, a very talented two-year-old Bold Executive colt, won the Frost King and the Kingarvie Stakes. Stablemate Shillelagh Slew is another talented two-year-old who finished 3rd in the Coronation and shows a lot of promise for next year – enough for DePaulo to get excited about the possibility of having a Queen’s Plate contender. Although Krz Ruckus is by far the most famous horse DePaulo has trained, that may be about to change. DePaulo feels that Shillelagh Slew is the best horse he’s ever conditioned and not just because he loves to run, but also due to his versatility. “There isn’t a surface he can’t run on,” says DePaulo.Winning the Queen’s Plate is the milestone DePaulo has been reaching for and a moment that now seems within his grasp.
In 2006 either, Shillelagh Slew or Bad Hat, (who went into winter quarters undefeated) could be the horse to put Mike DePaulo’s name in the University of Woodbine history books.