Evaluation of the thyroid status of Basenji dogs in Australia.

OBJECTIVE: To determine the thyroid status of Basenji dogs in Australia. METHODS: Jugular or cephalic venipuncture blood samples were taken from 113 Basenji, comprising 47 males, 5 castrates, 48 entire and 13 spayed bitches, and sent on ice in plain and EDTA tubes to a single laboratory to determine haematocrit and serum concentrations of total thyroid hormone (thyroxine, TT4), thyroid-stimulating hormone (TSH) and cholesterol. In a subgroup of 8 dogs with abnormal elevated TSH concentrations and subnormal TT4 concentrations, 5 were further examined by dynamic endocrine testing using recombinant human (rh) TSH (54 microg). RESULTS: Ages ranged from 1 to 14 years and weight range was 6.5 to 14.0 kg. TT4 concentrations (nmol/L) ranged from 2 to 27, with a median of 13 and a mean +/- SD of 13.0 +/- 5.7. Importantly, 85/113 (75%) of TT4 values were lower than the normal laboratory reference range (17-37). TSH concentrations (ng/mL) ranged from 0.05 to 5.37, with a median of 0.16 and a mean +/- SD of 0.3 +/- 0.6. CONCLUSIONS: Basenji have a similar reference range for serum TSH, but a considerably lower reference range for TT4 (2-27 nmol/L) than most breeds and crossbreds, resembling the sight hounds in this respect. Given the difficulty of accurately measuring TT4 concentrations that are so low, concomitant serial TSH determinations are essential to properly asses thyroid function. Taken alone, TT4 determinations are only of use when the value is within the reference range, in which case a diagnosis of hypothyroidism is likely excluded.

Ergogenic aids to performance in the race horse: nutrients or drugs.

Since the domestication of the horse and its use in various types of athletic competition, its diet has developed from that associated with grazing to feeding of additional energy in the form of grains up to the present situation when numerous supplements are fed in hopes of enhancing performance. Many if not all of these may be considered as ergogenic aids, and under the rules of racing in many countries should be considered as a prohibited substance. Until recently, a blind eye has been turned to whether the rules should be enforced against many nutritional supplements, for example, vitamins and amino acids, especially when given in amounts vastly in excess of normal requirements. However, although arguably a nutrient, large doses of sodium bicarbonate and possibly other compounds with the potential of improving buffering capacity have been used extensively, and rules and detection methods have been introduced to curtail this. This paper reviews the nutritional supplements currently in use and discusses whether the singling out of alkalinizing agents as an enforceable prohibited substance is justified, whereas other substances such as fats can be supplemented in high amounts.

Anabolic steroids.

Anabolic steroids have been employed extensively in equine practice over the past 25 years. Their usefulness is largely dependent on subjective opinions, as only minimal studies have been carried out in horses. Therefore, their use will vary markedly between practitioners depending on their personal experiences and pressures by trainers to use them. They form part of rational therapy in a variety of conditions. In addition to use for increasing muscle mass, they are used to a varying extent in the raising of yearlings and in the training and racing of horses with the view of improving performance. However, in almost all countries, the latter use is largely curtailed, and the presence of these substances in postrace urine samples constitutes use of an illegal substance. To detect the use of anabolic steroids, including testosterone, sensitive ELISA tests for screening and GC/MS for confirmation have been developed. These compounds can be used safely. Risks can be encountered if too high doses are used, as horses may become difficult to manage due to increased aggressiveness and other stallion-like behavior. Reproductive efficiency in both stallions and mares may be temporarily impaired, but this is quite rapidly reversible following cessation of treatment.

Correlation of racing performance with blood lactate and heart rate after exercise in thoroughbred horses.

At 2 and 5 mins after an 800-m gallop, venous blood was collected from 26 Thoroughbred racehorses for measurement of blood lactate concentration, packed cell volume (PCV) and haemoglobin concentration. In addition, 14 racehorses were given a strenuous submaximal treadmill exercise test. Heart rates during and after exercise at 10 m/sec on a treadmill inclined at 5 degrees were recorded. Blood samples at 2 and 5 mins after exercise were used to measure PCV, blood and plasma lactate and ammonia concentrations. Results of each exercise test were compared with the retrospective performance of horses in races, using Timeform ratings. The results of the field tests were also compared with the performance of each horse in a race 2 days later. There were no significant correlations between any of the measurements taken after the field test and either subsequent race performance or Timeform rating. Heart rate 4 mins after treadmill exercise was significantly correlated with Timeform rating (r = -0.565, P < 0.05). Blood and plasma lactate concentrations 2 and 5 mins after treadmill exercise were all significantly correlated with Timeform. The highest correlations were with blood lactate concentrations 2 and 5 mins after exercise (r = -0.68, P < 0.01). There were no significant correlations between Timeform and heart rate during exercise at 10 m/sec, heart rates at 1, 3 and 5 mins after exercise, PCV and plasma ammonia at 2 and 5 mins, or the differences between lactate concentration in plasma or blood at 2 and 5 mins after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory and cardiovascular adjustments during exercise of increasing intensity and during recovery in thoroughbred racehorses.

A new design of flowmeter is described and used in a comprehensive study of the respiratory and cardiovascular adjustments that occur during a standardised exercise test in Thoroughbred horses. The flowmeter system and associated lightweight, fibreglass mask (total mass, 0.7 kg) have a maximum dead space of 500 ml and negligible resistance to airflow. They have no systematic effect on blood gases and, together with a rapidly responding mass spectrometer, enable an accurate computation of gas exchange to be performed together with breath-by-breath determination of other respiratory variables. At the highest level of exercise (12 ms-1 on a 3 degrees incline), the rate of oxygen uptake (VO2) and carbon dioxide production (VCO2) increased to 29.4 times and 36.8 times their resting values, respectively. Respiratory minute volume (VE) increased to 27.0 times its resting value, with respiratory frequency (fR) making the major contribution at the walk and trot. However, with increasing cantering speeds, fR changed little as it was locked in a 1:1 fashion to stride frequency, and tidal volume (VT) then made the major contribution to the increase in VE. The ratio of ventilatory dead space (VD) to VT in resting horses was lower than that previously reported in the literature and this could be the result of the different respiratory recording systems that were used. There was a close relationship between VT and stride length at increasing cantering speeds. Despite the fact that alveolar ventilation (VA) was well matched to VO2, there was a significant reduction in arterial PO2 (PaO2) when the horses cantered at 8 ms-1 and this eventually fell to 34% below the resting value. The present data tend to support the idea that VA/Vb (where Vb is cardiac output) inequalities are important in causing this hypoxaemia. However, the reduction in PaO2 was more than compensated for by an increase in haemoglobin concentration, [Hb], so the concentration of oxygen in the arterial blood (CaO2) was significantly above the resting value at all levels of exercise. Both lactate concentration and PaCO2 increased during exercise, causing substantial reductions in pH of both arterial and mixed venous blood. This would have inevitably shifted the oxygen equilibrium curve of the Hb to the right, desaturating the arterial blood and thus exacerbating the effect of the hypoxaemia, as would the almost 4 degrees C rise in blood temperature. The tight respiratory/locomotor linkage might prevent the acidosis and hyperthermia having the stimulatory effects on VE that they have in humans at high work loads.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of high-intensity exercise on plasma catecholamines in the thoroughbred horse.

In Study 1, a single speed test of 6 to 12 m/sec was performed for 2 mins at an incline of 5 degrees on a high-speed treadmill (single-step test). Only one speed was performed per session and blood samples were taken before and after the test. In Study 2 horses cantered for 1 min at increasing speeds of 6 to 13 m/sec on an incline of 3 degrees (multiple-step test). Blood samples were taken before exercise, throughout the test and during recovery. In the single-step test plasma concentrations of adrenaline and noradrenaline both increased at speeds of 9 m/sec, as did blood lactate. Mean concentrations of adrenaline and noradrenaline at the end of the 12 m/sec test were 153 and 148 nmol/litre, respectively. Plasma concentrations were similar over all speeds although there was a tendency for the increase in noradrenaline to be greater than that of adrenaline at the lower speeds. The multiple-step test resulted in smaller increases in both adrenaline and noradrenaline. Although again closely correlated, increases in adrenaline were 20-30% greater than those for noradrenaline. In both exercise models, changes in plasma adrenaline and noradrenaline values with exercise showed an exponential relationship to plasma lactate. A plasma half-life of less than 30 secs was indicated during recovery from the multiple-step test. Changes in adrenaline and noradrenaline were much greater than previously recorded in man and emphasise the importance of catecholamines in mediating the physiological response of the horse to exercise.

Plasma potassium and lactate concentrations in thoroughbred horses during exercise of varying intensity.

To investigate the effect of moderate to high intensity exercise of up to 6 min duration on plasma potassium and lactate concentrations, 6 Thoroughbred horses were studied using a treadmill at a 5 degree incline. Each test consisted of an 8-min standardised warm-up followed by an exercise bout at 8, 9, 10 or 12 m/sec. The horses were galloped at each speed for up to a maximum of 6 min or until signs of fatigue were present. The horses were then walked at 0 degree incline. Carotid arterial blood samples were taken during and after the exercise. At 8, 9 and 10 m/sec there was a general pattern of an initial rise in potassium to a peak around 1.5 min of exercise with the concentration then slowly decreasing. At 12 m/sec there was a continuous rise to a peak at the end of exercise in all horses. Immediately after exercise there was a rapid return (within 3-4 min) to the potassium concentrations recorded at the end of the warm-up period. Plasma lactate peaked around the end of exercise at all speeds. At the highest intensity of exercise the mechanisms for the re-uptake of potassium did not appear to be able to match the rate of efflux. In contrast, at less intense work loads, the rate of re-uptake appeared to be similar to or slightly greater than the rate of efflux. It is possible that a disturbance in this balance between efflux and re-uptake could result in a disturbance in normal neuromuscular function during exercise.

Muscle ATP loss and lactate accumulation at different work intensities in the exercising Thoroughbred horse.

The effect of 2 min treadmill exercise, at speeds of 6-12 m.s-1 on an incline of 5 degrees, upon muscle adenine nucleotide loss and lactate accumulation was studied in six Thoroughbred horses. Minimal change occurred in the adenosine triphosphate (ATP) content of the middle gluteal muscle at speeds of 10 m.s-1 or less, but significant loss (up to 47%) had occurred in all horses by 12 m.s-1. The decline in ATP significantly correlated with the accumulation of muscle lactate, beginning shortly after the accumulation of 40 mmol.kg-1 dry muscle lactate. Decline in muscle ATP was mirrored closely by the appearance of ammonia, and to a lesser extent, hypoxanthine and uric acid in plasma. The results suggest that peak accumulation of any of these, or simply the concentration at a specified recovery time, may be used as a measure of ATP loss in the musculature as a whole. This was not so in the case of xanthine, which may also be formed from the degradation of guanidine nucleotides. An In-In plot of plasma ammonia against treadmill speed indicated a break point in accumulation between 8 and 9 m.s-1. The kinetics of ammonia accumulation with speed differed from those of lactate.

The influence of metabolic alkalosis upon exercise metabolism in the thoroughbred horse.

Six thoroughbred horses exercised on a motorised treadmill on two separate occasions at a speed of 11 or 12 m.s-1 for up to 2 min. 4 h prior to exercise each horse was given a 21 test solution of sodium bicarbonate (NaHCO3; 0.6 g.kg-1 body mass) or a control solution of water by nasogastric intubation, the order of administration of the two solutions was randomised. Blood samples (n = 15) were obtained before and during the 4 h after intubation, during exercise and for 30 min after exercise. NaHCO3 ingestion resulted in changes in pre-exercise acid-base status. The changes in blood lactate and base excess with exercise were greater after NaHCO3 administration; after 1 min of exercise in the case of lactate (P less than 0.05) and immediately after exercise in the case of base excess (P less than 0.05). Plasma ammonia levels were lower during (P less than 0.05) and immediately after (P less than 0.05) exercise following NaHCO3 ingestion. The peak change in plasma ammonia with exercise was also lower after NaHCO3 ingestion (P less than 0.05). Following exercise after NaHCO3 ingestion, five horses demonstrated lower muscle adenosine 5-triphosphate loss (P less than 0.05) and inosine 5-monophosphate formation (P = 0.05) and higher glycerol 3-phosphate formation (P less than 0.05). There is evidence to suggest that metabolic alkalosis may delay the onset of fatigue by decreasing the extent of adenine nucleotide loss during high-intensity exercise.

Bioavailability of ascorbic acid in horses.

The bioavailability of ascorbic acid administered to thoroughbreds by intramuscular injection was investigated. For intramuscular injection two preparations were studied, and the percentage bioavailability up to 24 h of 10 g of ascorbic acid was 95% +/- 22 in four horses and 60% in two horses with preparations A and B, respectively. Bioavailability at 24 h in three horses injected subcutaneously with 10 g of preparation B was 82%. Intramuscular injection of both preparations was apparently well tolerated while subcutaneous injection of preparation B (pH 6.0) was associated with marked irritancy. In a cross-over trial in seven thoroughbreds the effect of 13 or 15 days of oral administration of crystalline ascorbic acid (20 g) or ascorbyl palmitate (47 g) on plasma ascorbic-acid concentrations was investigated. Marked differences occurred between individuals. There was a greater increase in plasma ascorbic-acid concentration with ascorbyl palmitate compared to ascorbic acid at 6 and 24 h following administration. In two horses there was no increase in plasma ascorbic acid at 6 h following either oral preparation. The finding of lowered plasma ascorbic-acid concentrations following a period of supplementation warrants further investigation to assess its significance.

Mechanics of breathing during strenuous exercise in Thoroughbred horses.

The changes induced by exercise on the mechanics of breathing, as well as the simultaneous changes occurring in arterial blood gas tensions and in respiratory gas exchange were investigated in 6 healthy thoroughbred horses, performing a treadmill exercise of increasing intensity. Respiratory airflow and tidal volume (VT) were measured with ultrasonic flowmeters. Pleural pressure changes were measured by an oesophageal balloon catheter. Gas concentration of the expired air was analysed with a mass spectrometer; the oxygen consumption (VO2) and the carbon dioxide output (VCO2) were computed breath-by-breath. Arterial blood gas values were obtained by sampling from the carotid artery. Between rest and fast gallop VT, respiratory frequency, expired minute ventilation (VE), VO2, VCO2, total pulmonary resistance (RL), mechanical work of breathing (Wrm) and PaCO2 increased significantly while PaO2 decreased significantly. The Wrm.VO2(-1) ratio in galloping horses increased exponentially with VE. This, together with the relationship between the changes in PaO2 and in PaCO2 and the increase in the ventilatory mechanics parameters, suggests that the mechanics of breathing may be one of the factors constraining further increase in ventilation in exercising healthy horses.

Effects of exercise and adrenaline on equine erythrocyte ATP content.

To investigate the claim that equine erythrocytes released from the spleen are older cells than those found at rest in the circulation, the 2,3, diphosphoglycerate (2,3 DPG), adenosine triphosphate (ATP) and creatine concentration of erythrocytes before and following splenic emptying were examined. Normal values for thoroughbreds (43) and ponies (10) at rest were established. Following either exercise or intravenous injection of adrenaline in six thoroughbreds, there was an increase in erythrocyte creatine content and a decrease in ATP concentration. Exercise produced a slight increase in 2,3 DPG while no change occurred with adrenaline. In two splenectomised ponies adrenaline only produced a decrease in erythrocyte ATP, with no change in creatine or 2,3 DPG content. It was concluded that erythrocytes released from the spleen are not aged cells. However, the stimuli used produced a decrease in ATP content which may affect the properties of the erythrocytes.

Association between muscle acetyl-CoA and acetylcarnitine levels in the exercising horse.

Treadmill exercise of 2-min duration and increasing intensity resulted in increased formation of acetyl-CoA and acetylcarnitine in working muscle of Thoroughbred horses. At high work intensities a plateau was reached for both acetyl-CoA (approximately 50 mumols/kg dry muscle) and acetylcarnitine (approximately 20 mmol/kg dry muscle). Postexercise concentrations were significantly (P less than 0.001) correlated; [acetylcarnitine] = 349.[acetyl-CoA] + 2.4. The results indicate that approximately 350 mumols acetylcarnitine were accumulated for every 1 mumol acetyl-CoA. Under the conditions of exercise used it is probable that most of the acetyl-CoA formed is generated through the intramitochondrial decarboxylation of pyruvate. The acetyl groups of acetyl-CoA are apparently redistributed throughout the whole cell through formation of acetylcarnitine, which readily transverses the mitochondrial membrane. Despite the redistribution, however, the close correlation between acetylcarnitine and acetyl-CoA would indicate that equilibrium was maintained and that neither acetylcarnitine transferase nor carnitine/acetylcarnitine translocase were rate limiting. There is some question as to whether the changes observed relate directly to exercise itself or to the state in muscle 10 s or more after exercise.

Some factors influencing plasma AST/CK activities in thoroughbred racehorses.

Sixty-six Thoroughbred horses in training (2 or 3 years of age) were studied during one flat racing season, to investigate the relationship between age, sex, time of year, dietary electrolyte imbalances and plasma aspartate aminotransferase/creatine kinase (AST/CK) activities. Management and training variations were minimised. Between February to October, monthly 24 h post exercise samples were collected and analysed for AST and CK activities. Sex and/or age were shown to have a significant effect on the occurrence of high CK (> 100 iu/litre) and AST (> 300 iu/litre) activities. Fillies were more likely to have elevated CK and AST than colts. Two-year-olds tended to have higher AST activities than three-year-olds. Time of year had no significant effect on the number of animals with high or low activities. Fourteen animals had consistently raised plasma AST activities (median > 300 iu/litre). Eight of these raced and seven won at least one race. The average daily intake of calcium, sodium, phosphorus and potassium was determined at each sampling time. In eight of the horses, the fractional electrolyte excretion (FE) of phosphate (PO4) and sodium (Na) was determined monthly. FE values were also determined in three horses which had suffered repeated attacks of the equine rhabdomyolysis syndrome. The FE, PO4 and Na values reflected dietary intake of calcium, phosphorus and sodium respectively. It was not possible to determine any effect of training or a predisposition to equine rhabdomyolysis. No obvious differences were found between the resting thyroxine values of three animals with consistently low AST activities, six of those with consistently raised AST and three animals which had suffered repeated attacks of rhabdomyolysis.

Bicarbonate loading in the thoroughbred: dose, method of administration and acid-base changes.

Two studies were undertaken in an attempt to investigate the optimal dose, route and time course required to 'bicarbonate load' the Thoroughbred. During the first study a test solution of sodium bicarbonate (NaHCO3) and a control solution of water were administered via a nasogastric tube to six horses. Blood acid-base status was determined immediately prior to and for 24 h following intubation. During the second study a standardised feed was given to four horses, with and without NaHCO3 supplementation. This was followed by a further trial involving the addition of glucose and NaHCO3 to a standardised feed. During Study 1, plasma pH peaked 8 h after NaHCO3 intubation (7.433 +/- 0.020) and levels were still elevated above control values 12 h post intubation. Although there was a trend for blood PCO2 to be elevated above control values at all times after NaHCO3 administration, values were only significantly different at 4 and 5 h post intubation. The patterns of change in plasma HCO3- and blood base-excess after NaHCO3 administration were similar. Values peaked between 3 and 6 h post intubation and were still above control values 12 h post intubation. In Study 2 attempts to alter acid-base status by presenting NaHCO3 mixed with feed were unsuccessful because horses failed to consume the total mix, despite attempts to mask the unpalatable nature of the feed by adding glucose. The results suggest that future studies investigating the influence of NaHCO3 on exercise performance and metabolism should possibly involve administration of NaHCO3 in a greater quantity than is administered conventionally (0.3 g/kg). More meaningful results may be obtained if NaHCO3 is administered as a solution, via a nasogastric tube, at least 3 h prior to exercise.

Haematological, biochemical and physiological changes in horses and ponies during the cross country stage of driving trial competitions.

The haematological, biochemical and physiological changes associated with the cross-country stage of driving trials were studied in horses and ponies competing in singles, pairs, tandems and teams at five, five-section and two, three-section events. Heart rates were monitored continuously and sometimes exceeded 200 beats/minute. The highest maximum, mean and recovery heart rates were found after the most severe competitions. Rectal temperatures were also highest after the most severe events and in some animals exceeded 41 degrees C. Respiratory rates were very variable. Blood taken five minutes after the cross-country showed a marked increase in haematocrit and a leucocytosis. Total plasma protein concentration increased by about 9 per cent but there was little change in the concentrations of plasma electrolytes. There was a very variable increase in plasma lactate concentration, the increase being related to the severity of the event; plasma lactate concentration occasionally exceeded 10 mmol/litre. Plasma glucose was also increased. The activities of plasma creative kinase and aspartate aminotransferase were only slightly increased after the cross-country stage.

Muscle buffering capacity and dipeptide content in the thoroughbred horse, greyhound dog and man.

1. Muscle buffering capacity (beta m) and dipeptide content were measured in locomotory muscles of the Thoroughbred horse, Greyhound dog and Man. 2. Beta m and carnosine contents were highest in the horse. Anserine was only found in dog muscle. 3. The higher beta m in horse and dog muscle, compared with man, appears to be predominantly due to higher muscle contents of histidine containing dipeptides in these species.

Hypoxanthine phosphoribosyltransferase activity in tissues and hypoxanthine concentrations in plasma and CSF of the horse in comparison with other species.

1. Plasma hypoxanthine and xanthine concentrations are very low in the horse and low in rat, mouse and greyhound compared to concentrations in beagles, man, sheep and rabbit. 2. Activities in erythrocytes of the main enzyme metabolizing hypoxanthine, hypoxanthine phosphori-bosyltransferase, show a similar pattern (Tax et al., 1976, Comp. Biochem. Physiol. 54B, 209-212); thus low activities have been found where plasma concentrations were low. 3. Hypoxanthine phosphoribosyltransferase activities in horse tissue other than erythrocytes are similar to those in man and rabbit with high activities in brain; this enzyme may therefore be functionally important in equine brain.

Effect of freeze-drying on measurements of pH in biopsy samples of the middle gluteal muscle of the horse: comparison of muscle pH to the pyruvate and lactate content.

Muscle biopsies taken after exercise, in comparison to those at rest, contain increased amounts of blood and this is a particular problem in studies of the horse. The inclusion of blood in muscle will introduce an upward bias in values of pH measured in muscle homogenates. In an attempt to control this, muscle biopsy samples of the middle gluteal from Thoroughbred horses were freeze-dried and dissected free of blood before determination of pH. Following exercise, muscle pH measured after freeze-drying was similar to that measured in homogenates prepared from frozen samples. In contrast, freeze-drying appeared to increase muscle pH in samples taken at rest. This was probably the result of loss of CO2 during freeze-drying. Muscle pH determined in freeze-dried samples taken at rest and after exercise was linearly related to pyruvate and lactate content (P less than 0.001). It is concluded that muscle samples taken after exercise can be freeze-dried and dissected free from blood before determination of pH, whereas this procedure will cause an alkaline shift in samples taken at rest.