Preliminary Studies on the Concentration of Na+,K+-ATPase in Skeletal Muscle of Draught Cattle in Mozambique: Effect of Sex,Age and Training

The effect of training on the potential for work in draught cattle was assessed by measuring the Na⁺,K⁺-ATPase in the muscle cell membrane and the elevation in the concentration of K⁺ in plasma during exercise. Biopsies of the semitendinosus muscle and venous blood samples were taken from the cattle used for draught work in Mozambique. No differences were found in the plasma ion or Na⁺,K⁺-ATPase concentrations in samples taken from Nguni, Africander and Angoni breeds. There were no significant differences in plasma ions (Na⁺, K⁺ and Cl^–) or muscle Na⁺,K⁺-ATPase concentrations between the Angoni males and females, although the males showed an increase in Na⁺,K⁺-ATPase with age, while the females showed a decrease. The increase in males might be attributed to their higher level of activity in the herds than that of females. After a training period of 15 days, a significant increase in Na⁺,K⁺-ATPase concentration in semitendinosus muscle was found in Angoni cattle. In females, this was significant after 8 days of training (about 30%); in males after 15 days of training (about 16%). On day 15, there was a reduction in the elevation of plasma K⁺ during the 2 h of draught work, indicating an increased capacity of the Na⁺,K⁺ pumps to maintain the extracellular K⁺ concentration in working muscles and a possible delay in the moment of fatigue.     

Effects of training on potassium homeostasis during exercise and skeletal muscle Na+,K(+)-ATPase concentration in young adult and middle-aged Dutch Warmblood horses

OBJECTIVE: To investigate the effects of moderate short-term training on K+ regulation in plasma and erythrocytes during exercise and on skeletal muscle Na+,K(+)-ATPase concentration in young adult and middle-aged horses. ANIMALS: Four 4- to 6-year-old and four 10- to 16-year-old Dutch Warmblood horses. PROCEDURE: The horses underwent a 6-minute exercise trial before and after 12 days of training. Skeletal muscle Na+,K(+)-ATPase concentration was analyzed in gluteus medius and semitendinosus muscle specimens before and after the 12-day training period. Blood samples were collected before and immediately after the trials and at 3, 5, 7, and 10 minutes after cessation of exercise for assessment of several hematologic variables and analysis of plasma and whole-blood K+ concentrations. RESULTS: After training, Na+,K(+)-ATPase concentration in the gluteus medius, but not semitendinosus, muscle of middle-aged horses increased (32%), compared with pretraining values; this did not affect the degree of hyperkalemia that developed during exercise. The development of hyperkalemia during exercise in young adult horses was blunted (albeit not significantly) without any change in the concentration of Na+,K(+)-ATPase in either of the muscles. After training, the erythrocyte K+ concentration increased (7% to 10%) significantly in both groups of horses but did not change during the exercise trials. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, the activation of skeletal muscle Na+,K(+)-ATPase during exercise is likely to decrease with age. Training appears to result in an increase in Na+,K(+)-ATPase activity in skeletal muscle with subsequent upregulation of Na+,K(+)-ATPase concentration if the existing Na+,K(+)-ATPase capacity cannot meet requirements.     

Effect of show jumping training on the development of locomotory muscle in young horses

OBJECTIVE: To investigate whether training for show jumping that is commenced early after birth affects the characteristics of equine locomotory muscle. ANIMALS: 19 Dutch Warmblood horses. PROCEDURES: Horses were assigned to a trained or not trained (control) group. After weaning, training (free jumping [2 d/wk] that was alternated with a 20-minute period of exercise in a mechanical rotating walker [3 d/wk]) was started and continued until horses were 3 years old. Fiber type composition (determined from myosin heavy chain [MyHC] content), fiber area, diffusion index (area supplied by 1 capillary), citrate synthase activity, and Na(+),K(+)-ATPase content were assessed in gluteus medius muscle specimens collected at 0.5, 1, 2, and 3 years. RESULTS: Developmental changes included an increase in MyHC fiber type IIa and a decrease in type IIad; increases in fiber area, diffusion index, and citrate synthase activity; and a decrease in Na(+),K(+)-ATPase content. The MyHC fiber type I and type IId were detected in high and low proportions, respectively. Training increased Na(+),K(+)-ATPase content, but did not affect other variables. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, show jumping training at an early age resulted in increased Na(+),K(+)-ATPase content of the deep portions of the gluteus medius muscle. The lack of training effects on the other muscle characteristics can partly be explained by the fact that an appropriate (aerobic) fiber type composition was already established at training commencement. These data also suggested that the developmental changes in equine muscle represent sufficient adaptation to meet the demands of this specific training.     

Management practices followed for draught cattle in the southern part of India

A study was conducted to determine the management practices followed by the farmers for draught cattle in Tamil Nadu state, India. Methods of procurement of animals, use of female animals, breeds preferred, housing, health, disposal of animals, feeding, shoeing, purchase of animal-drawn implements and their maintenance were all assessed with 210 farmers from seven districts across different agro-climatic zones in Tamil Nadu. The results revealed that 86 % of the respondents purchased the draught cattle from the livestock markets, most were bullocks but 20 small farmers and 5 medium farmers used female animals for ploughing. Among the indigenous breeds, Kangeyam (33 %) and Hallikar (30 %) breeds were the most popular for work. Most farmers (69 %) provided a mixed type of housing (provision of housing only during the night time and the rainy season) for their draught cattle. The major health problem reported by 63 % of respondents was pyrexia. Almost all farmers sold their animals at the age of 8–10 years. The feeding practices for draught cattle were poor especially with the small farmers. The cattle were fed with mainly paddy straw and rice bran. Oilcakes and cotton seeds were given to the animals which work throughout the year mainly for ploughing and carting. The draught cattle were first shod at around 2.5 years of age. The majority of the farmers (71 %) used the traditional animal-drawn implements made by local artisans, and the farmers were not aware of the new implements to reduce the drudgery of work cattle, designed by the Agricultural Machinery Research Centre and Agricultural Engineering Departments located in India.     

Effects of draught load exercise and training on calcium homeostasis in horses

This study was conducted to investigate the effects of draught load exercise on calcium (Ca) homeostasis in young horses. Five 2-year-old untrained Standardbred horses were studied in a 4-month training programme. All exercise workouts were performed on a treadmill at a 6% incline and with a constant draught load of 40 kg (0.44 kN). The training programme started with a standardized exercise test (SET 1; six incremental steps of 5 min duration each, first step 1.38 m/s, stepwise increase by 0.56 m/s). A training programme was then initiated which consisted of low-speed exercise sessions (LSE; constant velocity at 1.67 m/s for 60 min, 48 training sessions in total). After the 16th and 48th LSE sessions, SETs (SET 2: middle of training period, SET 3: finishing training period) were performed again under the identical test protocol of SET 1. Blood samples for blood lactate, plasma total Ca, blood ionized calcium (Ca(2+)), blood pH, plasma inorganic phosphorus (P(i)) and plasma intact parathyroid hormone (PTH) were collected before, during and after SETs, and before and after the first, 16th, 32nd and 48th LSE sessions. During SETs there was a decrease in ionized Ca(2+) and a rise in lactate, P(i) and intact PTH. The LSEs resulted in an increase in pH and P(i), whereas lactate, ionized Ca(2+), total Ca and intact PTH were not affected. No changes in Ca metabolism were detected in the course of training. Results of this study suggest that the type of exercise influences Ca homeostasis and intact PTH response, but that these effects are not influenced in the course of the training period.     

Specificity and reversibility of the training effects on the concentration of Na+,K+-Atpase in foal skeletal muscle

The purpose of the present study was to determine whether training and detraining affect the Na+,K+-ATPase concentration in horse skeletal muscles, and whether these effects are specific for the muscles involved in the training programme. Twenty-four Dutch Warmblood foals age 7 days were assigned randomly to 3 groups: Box (box-rest without training), Training (box-rest with training: short-sprint) and Pasture (pasture without training). Exercise regimens were carried out for 5 months and were followed by 6 months of detraining. Five of the foals in each group were subjected to euthanasia at age 5 months and the remaining foals at 11 months. Muscle samples were collected from the deep part of the gluteus medius, semitendinosus and masseter muscles. The Na+,K+-ATPase concentration was quantified by [3H]ouabain binding. In the Training group, the concentration of Na+,K+-ATPase in gluteus medius and semitendinosus muscle, but not in masseter muscle, showed a relative increase of 20% (P<0.05) as compared to Box foals. After detraining for the subsequent 6 months, the concentration of Na+,K+-ATPase in semitendinosus muscle remained the same, while that in gluteus medius muscle was reduced by 10%. It is concluded that: 1) short-sprint training for 5 months induced an increase of the Na+,K+-ATPase concentration in gluteus medius and semitendinosus muscles of the foal. Interestingly, this effect persisted during the 6 months of the detraining period. Whether the higher Na+,K+-ATPase concentration due to training of young foals leads to a better athletic performance when they become mature still needs to be established; 2) the factors that initiate an increase in Na+,K+-ATPase concentration following training are likely to be located in the muscle itself and 3) the training effect may last for several months after returning to normal activity, especially in muscles containing a high percentage of fast-twitch fibres.     

Exercise-induced hyperkalemia in hypothyroid dogs

We investigated the effect of hypothyroidism in dogs on (1) the Na+-, K+ -ATPase concentration in skeletal muscle, and (2) potassium (K+) homeostasis at rest and during exercise. Prior to and 1 year after induction of hypothyroidism by surgery and subsequent radiothyroidectomy, the Na+-, K+ -ATPase concentrations were quantified in biopsies of sternothyroid muscles of seven Beagle dogs by measuring [3H]ouabain binding capacity. In addition, plasma K+ concentrations were measured at rest and after treadmill exercise in six hypothyroid and seven euthyroid Beagle dogs. During hypothyroidism, the mean Na+ -, K+ -ATPase concentration in muscle biopsies was 41% lower than during euthyroidism. The mean resting plasma K+ value of the hypothyroid dogs was significantly (14%) higher than that of the euthyroid dogs. In the hypothyroid dogs, plasma K+ concentration increased significantly during exercise, whereas there was no rise in the euthyroid dogs. The rise in plasma K+ concentration could not be ascribed to muscle damage, as plasma creatine kinase concentrations remained within reference range. Also renal K+ retention was an unlikely explanation, as plasma aldosterone concentration and plasma renin activity rather increased than decreased during exercise. In conclusion, hypothyroid dogs tend to develop hyperkalemia during exercise, which for a large part can be explained by the severe reduction of the Na+ -, K+ -ATPase capacity in the skeletal muscle pool.     

Performance and Management of Draught Animals in Agriculture in sub-Saharan Africa: A Review

Use of animal power generally enables farmers in sub-Saharan Africa to increase agricultural production and improve the quality of life. Effective use of working animals depends on an understanding of the capabilities of the animals for work, their husbandry requirements and the factors which can influence their performance. These issues are reviewed in this paper in the context of the use of animal power in agriculture in sub-Saharan Africa. The type of animal used for work determines power available to the farmer. The performance of donkeys, horses and cattle have been compared in work tests. Equids are more suited to rapid low draught activities where their faster speed can be used to advantage. At higher draught forces, where speed is less important, the additional weight and power of cattle are an advantage. Use of heart rate recovery after work gives a reasonable indication of fatigue and fitness of equids, when test conditions are standardized. Although feed requirements for work are generally low, feed quality can be so poor that animals are unable to eat enough to meet energy needs for work, and so lose weight during the work season. However, improvements in work performance are not always seen following supplementary feeding in the dry season and the economics need to be considered in each case. Food availability, diseases and heat stress, the major constraints to performance of draught cattle and donkeys working in sub-Saharan Africa, are discussed.     

Effects of β-Hydroxy-β-Methylbutyrate and γ-Oryzanol on Blood Biochemical Markers in Exercising Thoroughbred Race Horses

In both the horse and the man, nutritional ergogenic aids have been used to improve physical ability in conjunction with an appropriate training regimen. Although training increases physical condition, the ease of taking a nutritional additive to improve training results explains the demand for supplementation, which may increase mechanical energy of work, delay onset of fatigue, or improve neuromuscular coordination. The purpose of this study was to determine the effects of oral supplementation of β-hydroxy-β-methylbutyrate (HMB) and γ-oryzanol (GO) on indices of exercise-induced muscle damage in Thoroughbred race horses. In this 32-week study, the horses were assigned to either a placebo, GO (3.0 g/d), HMB (15 g/d), or GO and HMB treatment groups. The supplements were administered for the first 16 weeks of the study during the training period before the racing season began. Blood samples were taken at baseline, and then during training, before exercise, immediately after exercise, and 30 minutes after exercise. Heart rate and speed were monitored in each exercise session. Hematocrit, glucose, lactate (LA), creatine phosphokinase, and aspartate aminotransferase were measured before and after each exercise session. Analysis of variance showed a significantly greater increase in postexercise creatine kinase activity in placebo-supplemented group than in the other treatment groups, both in the training period and during the racing seasons (P < .05). Blood LA was higher immediately after exercise in the placebo group compared with the supplemented groups. In conclusion, supplementation with HMB and GO resulted in decreased creatine kinase and LA after exercise. These findings support the hypothesis that HMB and GO supplementation helps to prevent exercise-induced muscle damage.     

Quantitative analysis of acid-base balance in show jumpers before and after exercise

The acid-base status of venous blood was studied in 17 show jumpers before and after exercise using both a traditional and a quantitative approach. Partial pressure of carbon dioxide (PCO(2)), pH, haemoglobin, and plasma concentrations of sodium (Na(+)), chloride (Cl(-)), potasium (K(+)), ionized calcium (Ca(2+)), total proteins, albumin, lactate and phosphorus were measured in jugular venous blood samples obtained before and immediately after finishing a show jumping competition. Bicarbonate, anion gap and globulin concentration were calculated from the measured parameters. 'Quantitative analysis' of acid-base balance was performed utilising values for three independent variables: PCO(2), strong ion difference [SID = (Na(+)+ K(+)+ Ca(2+)) - (Cl(-)+ Lact)] and total concentration of weak acids [A(T)= Alb (1 paragraph sign23 pH - 6 paragraph sign31) + Pi (0 paragraph sign309 pH - 0 paragraph sign469) 10/30 paragraph sign97]; plasma concentrations of hydrogen ion ([H(+)]) were also calculated from these variables using Stewart's equation. No significant changes in blood pH were detected after the show jumping competition. Exercise resulted in a significant increase in lactate, Na(+), K(+), haemoglobin, total proteins, albumin, globulin and anion gap, and a decrease in bicarbonate, Cl(-)and Ca(2+). PCO(2)decreased after exercise while SID and A(T)increased. A significant correlation between measured and calculated [H(+)] was found both before and after exercise. However, individual [H(+)] values were not accurately predicted from Stewart's equation. In conclusion, even though pH did not change, significant modifications in the acid-base balance of horses have been found after a show jumping competition. In addition, quantitative analysis has been shown to provide an adequate interpretation of acid-base status in show jumpers before and after exercise.     

The association of the presence of seminal plasma and its components with sperm longevity in fractionated stallion ejaculates

Semen jets in the stallion's ejaculate differ in both the biochemical composition of seminal plasma (SP) and in sperm concentration, forming sperm-rich fractions (HIGH) and sperm-poor fractions (LOW). This study examined (i) the association of the levels of selected components of SP [alkaline phosphatase (AP), acid phosphatase (ACP), Na(+), Cl(-), K(+), Ca, Mg and prostaglandin E(2)] with semen quality, sperm longevity and fertility; (ii) the effects of the presence of SP on sperm survival during cooled storage; (iii) the differences in the composition of SP between sperm-rich and sperm-poor ejaculatory fractions; (iv) the differences between these fractions in the effects of SP on sperm longevity. The levels of AP, ACP and Na(+) were higher in HIGH compared with LOW, whereas higher concentrations of Ca, K(+) and Mg were found in LOW than in HIGH. None of the measured components were correlated to the first cycle pregnancy rate. The presence of SP during cooled storage caused DNA degradation, but total and progressive sperm motility was not affected. Sperm-rich fractions stored with low levels of SP maintained higher level of DNA integrity compared with sperm-rich fractions in higher levels of SP, or sperm-poor fractions irrespective of the proportion of SP. The concentration of K(+) in LOW may give some indication on the maintenance of total sperm motility during cooled storage.     

Muscle glycogen depletion patterns during draught work in Standardbred horses

Muscle fibre recruitment was investigated during draught loaded exercise by studying glycogen depletion patterns from histochemical stains of muscle biopsies from the gluteus and semitendinosus muscles. Three Standardbred trotters performed several intervals of draught loaded exercise on a treadmill with 34 kp at a trot (7 m/sec) and with 34 and 80 kp, respectively at a walk (2m/sec). Exercise was continued until the horses were unwilling to continue. Glycogen depletion was seen in all three fibre types when trotting with 34 kp for 5 or 10 mins. When an equal weight resistance was pulled at a walk, glycogen depletion was first seen in type I fibres only, then followed by a small percentage of type IIA fibres after at least 1 h. When 80 kp was pulled at a walk both type I and IIA fibres showed glycogen depletion, and after at least 30 mins exercise a small percentage of type IIB fibres was also depleted. These results indicate that the muscle fibres are depleted, in order, from type I through IIA to IIB as the intensity or duration of draught work increases.     

Alterations of fluid and electrolyte balance in thoroughbred racehorses following strenuous exercise during training.

Alterations of acid-base status, and fluid and electrolyte balance subsequent to exercise in Thoroughbred racehorses in North America have not been well-characterized. Des-cribed here are the results of an observational study conducted to characterize changes in fluid and electrolytes following strenuous exercise of 16 Thoroughbreds under routine training conditions. Changes following strenuous exercise were determined for the following variables: serum concentrations of sodium (Na), potassium (K), chloride (Cl) and protein; pH of blood; osmolality of plasma and urine; body weight; and, fractional urinary excretion (FE) of Na, K and Cl. The following changes occurred during exercise: increased concentration of Na in blood; increased FE of Na; decreased concentration of Cl in blood; decreased FE of Cl; increased urinary and plasmal osmolality; weight-loss; decreased pH of blood; and, increased concentration of lactic acid. The concurrent decreased concentration of chloride in plasma and acidemia in these horses differed from the hypochloremic, metabolic alkalosis previously described among endurance horses. Acidemia was attributed to production of lactic acid by anaerobic glycolysis.     

Serotypes and virulence genes of bovine Shigatoxigenic Escherichia coli (STEC) isolated from a feedlot in Argentina

Grazing-fed cattle were previously demonstrated to be reservoir of non-O157 Shigatoxigenic Escherichia coli (STEC) serotypes in Argentina. The acid-resistance of some STEC strains makes it reasonable to assume the presence in feedlot of particular STEC serotypes. Fifty-nine animals were sampled every 2 weeks during 6 months by rectal swabs. Twenty-seven of 59 animals (45.8%) were shown to be Stx2(+); 3/59 (5.1%) carried Stx1(+) and 7/59 (11.9%) were Stx1(+) Stx2(+). Among 44 STEC isolates, 31 isolates were associated to 10 O serogroups (O2, O15, O25, O103, O145, O146, O157, O171, O174, O175) and 13 were considered non-typable (NT). Six H antigens (H2, H7, H8, H19, H21, H25) were distributed in 21 isolates whereas 23 were non-mobile (H-). Seventeen of 44 strains (38.6%) were eaeA(+) and 14 (31.8%) harbored the 60MDa plasmid. The megaplasmid (Mp) and eaeA gene were simultaneously found in a limited number of serotypes belonging to the enterohaemorrhagic E. coli (EHEC). E. coli O157:H7 strains, isolated from four (6.8%) animals, corresponded to the Stx2(+), eaeA(+), Mp(+) pattern. Three O157:H7 strains belonged to phage type 4 and the other strain was atypical. Many serotypes isolated from grain-fed cattle (O2:H25, O15:H21, O25:H19, O145:H-, O146:H-, O146:H21, O157:H7, O175:H8) also differed from those isolated by us previously from grazing animals. The serotypes O15:H21, O25:H19 and O175:H8 had not been identified at present as belonging to STEC. This work provides new data for the understanding of the ecology of STEC in grain-fed cattle and confirms that cattle are an important reservoir of STEC.     

Ca2+ ATPase in Dutch warmblood foals compared with Na+, K+ ATPase: intermuscular differences and the effect of exercise

We studied the effects of exercise without or with a subsequent period on pasture on Ca2+ ATPase concentration in foal skeletal muscle, and compared the results with those previously reported on Na+, K+ ATPase. Ca2+ ATPase was measured in homogenates as Ca2+-dependent steady-state phosphorylation from [gamma-32P]ATP. From day 7 after birth, 24 foals were divided into three groups: (i) staying in a box stall (Box); (ii) staying in a box stall with an exercise programme of an increasing number of sprints per day (Exercise); and (iii) staying on pasture (Pasture). Half of the foals (12 with four in each treatment group) were killed after 5 months. The remaining foals stayed on pasture until 11 months. In the 5-month Pasture group, Ca2+ ATPase concentration was 29.4 +/- 4.3 nmol/g wet weight (wt) (n = 4) in gluteus medius muscle, 25.2 +/- 3.3 nmol/g wet wt (n = 4) in semitendinosus muscle (both mixed fibre type), and 4.1 +/- 1.7 nmol/g wet wt (n = 3) in the slow masseter muscle. These values were not altered by exercise or by box rest. This was in contrast to the Na+, K+ ATPase concentration which was not different between the three muscles, but showed a 20% rise in gluteus medius and semitendinosus muscle after exercise. In the period from 5 to 11 months on pasture, there was no change in Ca2+ ATPase in any group. In conclusion, the Ca2+ ATPase concentration in foal muscle is around 6-fold higher in mixed fibres than in slow fibres. Furthermore, the enzyme is not up- or down-regulated by sprint exercise or subsequent rest.     

Blood and muscle metabolic responses to draught work of varying intensity and duration in horses

Three standardbred trotters performed treadmill exercise at a velocity of 2 m s-1 with a draught load of both 34 kiloponds (kp) (test 1) and 80 kp (test 2), and also at 7 m s-1 with 34 kp (test 3). The heart rate increased to average values of 111 (+/- 5), 157 (+/- 10) and 197 (+/- 7) beats min-1 in tests 1, 2, and 3, respectively. Plasma free fatty acids increased only during tests 1 and 2. Blood lactate and muscle glucose-6-phosphate and lactate concentrations were low after tests 1 and 2, but high after test 3, where also muscle glycogen utilisation was greatest. Muscle creatine phosphate and adenosine triphosphate concentrations decreased after test 3 only. The study indicates that oxidative metabolism is most important for energy supply in muscles when exercise is performed with draught loads of both 34 and 80 kp at a low velocity. Glycogenolysis with lactate accumulation and phosphagen breakdown becomes much more important when, with a draught load of 34 kp, the velocity of exercise increases.     

Mineral deficiencies in grazing dairy cattle in Kordofan and Darfur regions in western Sudan

The seasonal changes in mineral profiles in serum of grazing dairy cattle and the concentrations of nutrients available from forages were determined in western Sudan. Blood samples were collected seasonally from dairy cows, Kenana and Botana breeds, in 6 locations in Kordofan and Darfur. Data were analysed as a split-plot design with repeated measures. The results indicated there were significant seasonal changes in concentrations of P, Cu and K, Ca, Mg, Na, Co, and Zn in blood serum of grazing cows. Concentrations of P, Ca and Na in serum were lowest during the late dry season (4.5 mg/dl, 8.21 mg/dl and 129 mEq/L respectively), while concentrations of Cu, deficient throughout the year, were lowest during the rainy season (0.35 µg/ml). The interaction of location×season was significant for serum P, Ca, Cu, Mg, Na, Co and K. Kenana cattle had lower Zn in serum (0.96 µg/ml) than Botana cattle (1.13 µg/ml). During the dry season, forages had very low CP (3.5±0.5%), high neutral detergent fibre (NDF) (67.5±1.8%) and high acid detergent (ADF) (38.5±1.2%) content. Calcium, P and Na levels in forages were deficient during the dry season (0.38±0.03%, 0.08±0.03% and 0.047±0.01% respectively). Copper also was deficient in forages during the dry season, but adequate during the mid-rainy season (3.0±2.4 and 26.1±1.5 mg/kg respectively). In conclusion, the low Cu concentration in sera of cattle indicated a possible nutritional deficiency throughout the year, while P, Ca, and Na were low in sera during the late dry season. Thus, seasonal deficiencies of minerals may affect productivity of cattle in the Kordofan and Darfur regions of Sudan.     

Plasma beta-endorphin and adrenocorticotrophin in young horses in training

A controlled period of submaximal exercise on a treadmill was used as a standardised stress test in 6 young horses to monitor the effects of training. Circulating plasma concentrations of immunoreactive beta-endorphin (IR beta-EP) were measured before, during and after the exercise period. The stress test was conducted on 3 occasions during an intensive training program lasting 14 weeks. In week 3 a marked increase in plasma IR beta-EP (P = 0.003) was demonstrated as a result of training, but by the last exercise test performed in week 9 no significant increase in plasma IR beta-EP concentrations could be detected. During the training period the basal concentrations of plasma IR beta-EP significantly decreased (P = 0.0059). Plasma adrenocorticotrophin (ACTH) did not increase during exercise, although there was a trend of decreasing basal plasma ACTH by the end of the training period. It was concluded that a standardised work test acted as a mild stress to unfit horses, but as the horses' fitness increased the hormonal response to exercise diminished. Basal plasma beta-EP concentrations were decreased with increasing fitness.     

Circulatory and muscle metabolic responses to draught work compared to increasing trotting velocities

Circulatory and muscle metabolic responses were studied in 10 horses which all performed incremental draught work at a low trotting speed on a treadmill (D-test) and also exercise with gradually increasing velocities (S-test). Exercise was continued until the horses could no longer maintain the weights above the floor or maintain speed trotting without changing gait to a gallop. Muscle biopsies were taken from the gluteus and the semitendinosus muscles before, and immediately after, exercise. The heart rate (HR) increased linearly with both increasing draught resistance and velocity and reached mean values of 212 and 203 beats/min, respectively. Blood lactate levels increased exponentially to mean values of 12.9 and 7.9 mmol/litre in the two tests. Both HR and blood lactate levels were significantly higher at the cessation of work in the D-test compared to the S-test. The relationship between HR and blood lactate response in the S-test was similar to that in the D-test. The red cell volume was determined after a standardised exercise tolerance test and was significantly correlated both to the weightloading and to the velocity, producing a HR of 200 beats/min. The changes seen in muscle glycogen and glucose-6-phosphate were similar in the two tests, whereas significantly higher lactate levels and lower creatine phosphate and adenosine triphosphate levels were seen in the D-test compared to the S-test. It was concluded that high oxidative capacity is of importance both for fast trotting and for draught work.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise induced hormonal and metabolic changes in Thoroughbred horses: effects of conditioning and acepromazine

Nine Thoroughbred horses were assessed to determine the normal response of insulin, glucose, cortisol, plasma potassium (K) and erythrocyte K through conditioning and to exercise over 400 and 1,000 m. In addition, adrenaline, noradrenaline, cortisol, plasma K, erythrocyte K and L-lactate concentrations were evaluated in response to maximal exercise with and without the administration of acepromazine. Conditioning caused no obvious trends in plasma K, erythrocyte K, insulin or glucose concentration. Serum cortisol increased (P less than 0.05) from the initial sample at Week 1 to Weeks 4 and 5 (attributed to a response to training), and then decreased. During conditioning, three horses had low erythrocyte K concentrations (less than 89.3 mmol/litre). Further work is needed to define the significance of low erythrocyte K concentrations in the performance horse. In all tests maximal exercise increased plasma K, glucose and cortisol concentrations, whereas insulin and erythrocyte K concentrations decreased. Thirty minutes following exercise, plasma K and erythrocyte K concentrations returned to resting values; whereas glucose and cortisol concentrations continued to increase and the insulin concentration also was increased. The magnitude of the changes varied for pre-conditioned vs post-conditioned exercise tests and the duration of exercise. The administration of acepromazine prior to exercise over 1,000 m failed to alter the circulating noradrenaline and adrenaline concentrations in anticipation of exercise or 2 mins following exercise. Acepromazine administration, however, did cause lower L-lactate concentration 2 mins (P less than 0.03) and 30 mins (P less than or equal to 0.005) following exercise. Also, erythrocyte K showed a delayed return to baseline levels at 30 mins post exercise. Further evaluation of these trends may help explain the beneficial role acepromazine plays in limiting signs of exertional rhabdomyolysis when administered prior to exercise.