Different Racing Distances Effects On Metabolic Endurance Horses Biology Essay

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Endurance horses are generally exposed to severe stress during endurance competitions and as such they are conditioned to cover long distances at moderate speeds. Therefore, this study was conducted in order to investigate the relationship between hematological, biochemical, and physical parameters on the different riding distances of metabolic endurance horses. Blood samples were collected and analyzed for hematological and biochemical parameters. Physical examination was conducted on all participating horses. From the total of 72 metabolic endurance horses that were eliminated from the endurance ride, seven (9.72%) horses were eliminated from the advanced category (120 km), 48 (66.67%) horses were eliminated from the intermediate category (80 km) while 17 (23.61%) horses were equally eliminated from the racing category for amateurs (40km). The result showed mean elevated levels of band neutrophils, segmented neutrophils, icterus index, total bilirubin, creatinine, aspartate aminotransferase, lactate, CPK, total protein, albumin, glucose and calcium and decrease mean levels of RBC. The mean heart rate value of the metabolic endurance horses was 64.5±13.3 beats per minute while the mean gut motility was 1.6±0.6; the mean mucus membrane and skin recoil were 1.4±0.6 and 1.6±0.7 respectively. The mean age group affected lies between eleven to fifteen (11-15) years. The female and geldings had equal presentation in this study. There was a significant correlation between hematological, biochemical and physical parameters and the riding distances of metabolic endurance horses of P < 0.01, and the findings from this study could be used to differentiate between good and metabolic endurance horses base on distances covered.

Keywords: hematological parameters, biochemical parameters, physical parameters and riding distances of endurance horses.


Endurance horses undergo severe stress during the course of a competitive endurance ride. The criteria for determining whether a horse should be allowed to continue the race is by the assessment of the horse by a veterinarian through physical examination (e.g. general condition, signs of dehydration, hyperthermia, soreness and lameness) and its heart rate and respiratory rate (Cottin et al., 2006). Hematological and biochemical changes were evaluated by obtaining the post-ride blood samples. Hematocrit values, hemoglobin concentration, red blood cell count, heart rate, respiration rate and rectal temperature increased statistically with exercise, in comparison to the pre-exercise levels (Valberg, 2009).

Endurance horses are trained and conditioned to perform over long distances at moderate speeds. When conditioning a horse for long distance competition, the training program must be designed and monitored to match the specific exercise type and intensity of competitive endurance riding (Linder et al., 2006). The major physiological adaptations that can directly influence exercise capacity and stamina of endurance horses include the efficiency of gas exchange, oxygen uptake, and delivery to the exercising muscles. Endurance horses rely almost entirely on aerobic metabolism of muscle energy (glycogen), fatty acids (blood lipids) and volatile fatty acids from hindgut fermentation, the heart size and its capacity to deliver large volumes of blood to the working muscles (Williams et al., 2005).

Stress and fatigue induced by a long-distance race are clearly expressed by changes in red and white blood cells as well as creatinine. Tissue remodeling is clearly seen by changes in fibrinogen, urea, proteins and CK (Smith et al., 2006). Post-exercise blood lactate concentration can also be used to indicate the fitness of the horse. As a horse's fitness increases, post-exercise blood lactate concentrations should decrease. Anna and Smith (2006) found that training affected blood lactate concentration during a standardized exercise testing, where blood lactate concentration decreased after exercise as training duration increased. However, it was found that acute over-training was related to an increase in post-exercise blood lactate concentration (Anna and Smith, 2006). Maximal blood lactate steady state concentration and anaerobic threshold have been shown to predict long distance performance and training loads (Gondim et al., 2007). After exercise, accumulated lactate is cleared by oxidative pathways (Marsh et al., 2006).

Exercise is broadly recognized as a stressor, causing neuroendocrine and hormonal changes that can mediate alterations of immune functions, thereby increasing susceptibility to disease. Infections result in lost training time and decreased earnings over the course of the horse's athletic career. Although a reduction in training load could alleviate disease risk, this is most of the time impractical when preparing horses for competition. Hence, strategies to eliminate exercise-induced immunosuppression would be of greater benefit to the horse industry. Nutrition plays a supportive role in immunity, and some nutrients have the ability to cause immuno-stimulatory or modulatory effects when supplemented to the diet (Warren, 2008).

High calcium levels in blood is undesirable, Endurance horses require lots of calcium because calcium is needed for muscle contractions and inadequate plasma levels of calcium during strenuous exercise can cause metabolic problems and failures, including synchronous diaphragmatic flutter. However, high calcium levels may increase the frequency of thumps during endurance competitions (Lewis, 1995).

When a conditioned horse is not exercised and is given ratio high in carbohydrates the horse is bound to have high carbohydrates content in the muscles. When the horse is subjected suddenly to strenuous work, the body cannot remove the accumulated lactic acid completely and rapidly from the muscles. This in turn brings about vasospasms and ischemia leading to the lactic acid waste product remaining in the muscles. Hence, intracellular pH drops, the muscle cells are disrupted and crampy muscles develops (Kobluk., et al, 1995).

In a suspected tying-up horses there are elevated muscle enzymes in the plasma, such as creatinine kinase (CK) and aspartate aminotransferase (AST). Therefore, if the enzyme levels are elevated in the blood, this will cause tissue cells to be injured. AST is found in both muscle and liver cells, so elevated levels could be problematic in either muscle or liver, AST levels are raised in the blood by certain drugs or toxins. Creatine Kinase will indicate the level of muscle damage, while other elevated enzymes in the blood will indicate liver damage, and lactate dehydrogenase (LDH) will indicate whether muscle damage occurring is from skeletal or cardiac muscle (Hodgson., et al, 1994).

Horses with exertional rhabdomyolysis usually show signs of muscle stiffness, swinging hindlimb lameness, elevated respiratory rate, sweating, firm painful hindquarter muscles, and reluctance to move that lasts for several hours. There may be a decrease in the severity of clinical signs as horses get older. Subclinical episodes occur in some horses causing decreased performance and painful muscles (Valbergs, 2009).

Bilirubin, a breakdown product of hemoglobin, high levels is an indication of liver malfunction, or it could be related to hemolysis. Hemolysis can occur in many different ways, this include toxicity, drugs, infectious diseases and immune deficiency. Increased bilirubin values can be considered along with other factors such as alkaline phosphatase and (Gamma Glutamyl transpeptidases) GGTP (Hodgson., et al, 1994).

The manipulation of blood glucose levels is one of the controversial issues in endurance horse management. Horses exercising at typical endurance ride depend on the oxidation of fatty acids for energy production; some amount of glucose is required for most metabolic pathways and by some vital organs. The brain is unable to utilize any substrate other than glucose. At the same time, the animal body is able to store just small amounts in muscle and liver tissue, and its fluctuations during exercise is a major contributory factor of fatigue. Adrenalin also increases blood glucose levels, values measured in excited horses might be at the high end of the normal range (Rose, et al, 1983).

As veterinarians we are always seeking for better ways to tackle training and performance issues. Our clients challenge us to make earlier diagnoses, with their strange sense of subtle change in hand. Their complaints are often non-specific and difficult to pinpoint, e.g., complaints such as "lack of impulsion, "lethargy," "decreased endurance," "refusing jumps," and of course, "fading at the pole" in racehorses. Without consistent and specific signs, clinical examination can be difficult and unrewarding (Hoffman, 2001).

The objective of this study is to investigate the effect of riding distances on the significant hematological, biochemical, and physical parameters in relation to distances covered by metabolic endurance horses in a competition.



Approximately 72 metabolic endurance horses covered different distances of endurance ride of 120km, 80km and 40km respectively. Based on the racing category, 7 (9.72%) horses participated in 120 km, 48 (66.67%) horses went for 80 km category and 17 (23.61%) horses were in the category for amateurs (40 km).

Veterinary inspection at vet gate

Veterinary inspection was conducted on all competing horses and status of physical parameters was recorded. The physical parameters evaluated were the resting heart rate, cardiac recovery index (CRI), the gut sound, dehydration status, capillary refill time, color of mucous membrane, the muscle and anal tone and the gait soundness. Any soreness or injuries on the back, withers, girth area as well as the body and the distal extremities were recorded. All these parameters were re-evaluated and recorded each time the horses entered the vet-check after each leg of the race.

Sampling and equipments

Blood samples were obtained from the eliminated horses due to metabolic disturbances that were sent to the clinic for treatments using 21G needles in ethyldiaminotetra-acetic acid (EDTA) for whole blood analysis and lithium heparin for biochemistry analysis. Equipments used were the hematocrit centrifuge machine to obtain plasma for biochemistry analysis, the hematocrit centrifuge for hemoglobin concentrations analysis (Hettich-Hematocrit 210 and micro hematocrit reader-Hawksley), spectrophotometer (UV/visible-Secomam-Anthelie Advanced) as well as the automatic Hematology Analyzer Abbot-cell Dyn 3700) for blood cells count.


A total of 72 metabolic endurance horses were eliminated from the endurance competition, female and geldings have equal presentation of thirty two (44.44%) in respective of gender, while there were only eight stallions (11.11%). Seven (9.72%) horses were eliminated from the 120 km, 48 (66.67%) horses were also eliminated from the 80 km category and 17 (23.61%) horses were equally eliminated from the category for amateurs (40 km). The mean heart rate was 64.5±13.3 beats per minute; the mean gut motility was 1.6±0.6 while the mean mucus membrane and skin recoil were 1.4±0.6 and 1.6±0.7 respectively. The mean age was eleven to fifteen years (11-15) years. The hematological and biochemical parameters are presented in Table 1.




RBC (x1012/L) 40







Segmented Neutrophils (x109/L) 40







Band Neutrophils (x109/L) 40







Icterus index (Unit) 40







Calcium (mmol/L) 40







Creatinine (µmol/L) 40







Glucose (mmol/L) 40







Total Bilirubin (µmol/L) 40







Aspartate aminotransferase (U/L) 40







Creatinine Kinase (U/L) 40







Total Protein Serum (g/L) 40







Albumin (g/L) 40







Lactate (mmol/L) 40








From the assessment of the mean heart rate one will deduced from the study that the endurance horses were conditioned for the endurance ride prior to the endurance competition, and it was possible to estimate physical activity and energy expenditure from heart rate of horses with great deal of accuracy, after adjusting for age, gender, body mass and fitness and this agrees with the findings of (Geor, 2005).

Increases in the values of band and segmented neutrophils are suggestive of stress due to exercise and possible immunosuppression as a result of stress, and this is similar to the study conducted by Hoffman (2001), Bonsignore (2005) and Frisbie (2002).

In this study the increases in the value of icterus index and bilirubin are an indication of breakdown of hemoglobin due to endurance ride which is similar to the findings of Hodgson, (1994). Increased levels of bilirubin must be considered with other factors such as alkaline phosphatase and GGTP (Gamma Glutamyl transpeptidase) as suggested by Hodgson, (1994).

The increase in total plasma protein was suggestive of dehydration and this happened as a result of excessive sweating during endurance ride and this finding was similar to the study carried out by Kaneko, et al, (2008). The increase level of creatinine was as a result of insufficient excretion of the creatinine by the kidney as suggested in the findings of Kaneko, et al, (2008).

Elevated calcium levels in this study could be due to insufficient utilization of calcium for muscular contractions hence the resultant metabolic problems and failures, including synchronous diaphragmatic flutter which is similar to the suggestion of (Lewis, 1995).

The increase in glucose levels in this study perhaps is due to lack of glucose transporters into the muscles during and after the endurance ride as suggested by Hirshman, (1988) or it could be as a result of inherent insulin resistant receptors on the muscles or defective or insufficient secretion of insulin by the cells of islet of langerhans.

The decrease value of red blood cells in this study is perhaps the major causal factor of the metabolic problems due to insufficient oxygen supply and glucose as a nutrient to the muscles, tissues and other vital organs of the endurance horses especially the brain as pointed out by Rose, et al,(1983).

The mean lactate levels were elevated and therefore, this mean increase in lactate levels have a devastating effect on the tissues and organs of the competing endurance horses which was similar to the findings of Anna and Smith (2006).

Based on the number of horses eliminated from each category, the result indicates that the endurance horses that covered the 80 km distance have higher speed than the 40km horses because they are more robust and of higher speed than the 120 km horses because the distance covered is lesser and therefore require long distance conditioning regimen as pointed out by Linder et al. (2006) and of lactate removal from the systemic circulation via the oxidative pathway and this finding agrees with that of Marsh (2007).


In conclusion, the findings from this study could be used to differentiate between good and metabolic endurance horses' base on distances covered and using the significant hematological, biochemical parameters and the physical parameters.