ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05024.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05025.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryA theoretical integrative model was developed to determine the heat balance of horses working in a given environment. This model included the following parameters: metabolic heat gain, solar heat gain, evaporative heat loss due to sweating, respiratory tract heat loss, radiation from the body and heat gain or loss due to convection and conduction.The model developed in this study includes an unique approach for estimating heat loss via evaporation of sweat from the animal's skin surface. Previous studies modelling evaporative heat dissipation were based on the volume of sweat loss. While it is known that the ambient conditions affect evaporation rate, these effects have not been adequately described. The present model assumes the horse's skin surface is adequately represented by a body of water and it describes the interaction of that water body with the atmosphere.It is assumed that sweat has thermodynamic characteristics equivalent to distilled water. Sweat, however, has high electrolyte and protein concentrations and anecdotal evidence has shown that the thermodynamic characteristics may be significantly affected. Further research is, therefore, required to confirm these characteristics for equine sweat.The model describes all factors known to affect the thermal balance of the horse working in a given environment. The relative significance of the various variables on the whole integrative model has been illustrated. The effect of ambient temperature and humidity on the evaporative heat loss, the most significant and critical avenue of heat dissipation, is defined and quantified. The model illustrates clearly how increasing relative humidity limits evaporative heat loss, which can be further compromised when horses exercise on treadmills with no air movement.

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05026.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryHeart rate and gait characteristics (stride length and frequency) were studied in 6 horses subjected to a standardised incremental exercise test, involving moving at the trot and increasing speeds up to a fast gallop and subsequently during the steeplechase phase of a 3‐day‐event. The studies were performed in hot conditions. Appropriate scaling, based on hindleg length (hh), stride length (L), stride frequency (f) and speed (Sp) for nondimensional stride length (Λ = (L/hh), nondimensional stride frequency (φ = f(hh/g)1/2) and nondimensional velocity (û = Sp/(ghh)1/2), wheregis the gravitational acceleration, demonstrated that there were no major differences in characteristics over the full range studied Λ = 2.3 û0.68. However, there were subtle differences in some horses that could endow a benefit in locomotory efficiency when compared to others exercising at the same absolute speed. There were clear changes in the relationship between nondimensional stride length and frequency with increasing speed, from trot to canter (at û ⋍ 1.4) and to full gallop (at û ⋍ 2.3); when trotting, Λ was less than 2.2 and the transition from canter to gallop took place at Λ ⋍ 3.2.The cost of transport/kg/m, estimated from the heart rates measured continuously during each study, decreased with increasing speed and bodyweight. In some animals, there appeared to be a weak minimum around the canter‐gallop transition speed. When interpreted as oxygen cost, using published values for the oxygen consumption‐heart rate relationship, the cost fell from an average of 0.201 ml/kg/m at the trot to 0.161 mlO2/kg/m when galloping during the incremental exercise tests. During the steeplechase, the cost was approximately 7.5% higher than at the same speed in the exercise tests; this was probably due to jumping effort.Estimated power consumption increased linearly with speed. In the steeplechase, power consumption was also 7.5% higher than during the exercise tests at the same absolute speed; this was equivalent to an average rate of heat production of 346 kcal/min (24 kW) or 59.5 kcal/min/m2of the meas

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05027.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryDoes dietary fat supplementation during conditioning improve athletic performance, especially in the heat? Fat adaptation has been used to increase energy density, decrease bowel bulk and faecal output and reduce health risks associated with hydrolysable carbohydrate overload. It may also reduce spontaneous activity and reactivity (excitability), increase fatty acid oxidation, reduce CO2production and associated acidosis, enhance metabolic regulation of glycolysis, improve both aerobic and anaerobic performance and substantially reduce heat production. A thermochemical analysis of ATP generation showed the least heat release during the direct oxidation of long chain fatty acids, which have a 3% advantage over glucose and 20 to 30% over short chain fatty acids and amino acids. Indirect oxidation via storage as triglyceride increased heat loss during ATP generation by 3% for stearic acid, 65% for glucose and 174% for acetic acid. Meal feeding and nutrient storage, therefore, accentuates the advantage of dietary fat. A calorimetric model was based on initial estimates of net energy for competitive work (10.76 MJ for the Endurance Test of an Olympic level 3‐day‐event), other work (14.4 MJ/day) and maintenance (36 MJ), then applied estimates of efficiencies to derive associated heat productions for the utilisation of 3 diets,Diet A: hay (100),Diet B: hay and oats (50:50) andDiet C: hay, oats and vegetable oil (45:45:10), the difference between the last 2 diets representing fat adaptation. During a 90.5 min speed and stamina test, heat production was estimated as 37, 35.4 and 34.6 MJ for the 3 diets, respectively, an advantage 0.8 MJ less heat load for the fat adapted horse, which would reduce water needed for evaporation by 0.33 kg and reduce body temperature increase by about 0.07°C. Total estimated daily heat production was 105, 93 and 88 MJ for the 3 diets, respectively, suggesting a 5 MJ advantage for the fat adapted horse (Diet Cvs.Diet B). Estimated intake energy was 348, 269 and 239 MJ for the 3 diets, respectively, and corresponding daily intakes as fed were 22.2, 16.6 and 12.9 kg, an advantage of 3.7 kg for the fat adapted horse. Water requirement was estimated to decrease by about 6 kg/day in the fat adapted horse: 4 kg less faecal water output and 2 kg less water for evaporation. This model indicated that the fat supplemented diet reduced daily heat load by 5%, feed intake by 22%, faecal output (and bowel ballast) by 31% and water requirement by 12%. The advantage of fat supplementation over hay and oats was in general about half that gained by hay and oats over hay alone.The physiological challenges to a horse exercising competitively in the heat are exactly those that introduced physics and chemistry to biology and medicine. Antoine Lavoisier showed that combustion produced heat and acid, using an acid forming element that comprised about one‐fifth of air, which he called oxygene (acid‐former). He found that body heat and urine acid were increased by exercise and by certain foods. History has burdened Lavoisier as a scientific father figure, first as the Father of Chemistry, because he explained chemical reactions by means of weights and measures, that is, physics (his system of weights and measures developed into the metric). He then became known as the Father of Physiology, Nutrition and Medicine, because he explained these subjects in terms of chemistry and physics. He applied science to farming and it was his leadership in agriculture as a farmer‐generale that led him to the guillotine, M

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05028.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryIn this study, 4 Standardbred geldings were exercised at 20 and 35°C. The exercise test (ET) consisted of 2 exercise bouts separated by 2 h of rest in their boxes. Blood samples were taken before, during and after the second exercise bout and muscle (m. gluteus medius) biopsies were taken before the first exercise bout and after an intensive trot over 2600 m in the second exercise bout. The blood samples were analysed for plasma potassium and total plasma protein concentration (TPP) and the muscle fibres were analysed for elemental composition by x‐ray microanalysis. The intracellular content was as follows: sodium (Na) = 40 ± 7; magnesium (Mg) = 32 ± 4; phosphorus (P) = 282 ± 15; sulphur (S) = 222 ± 13; chloride (Cl) = 119 ± 31; potassium (K) = 304 ± 21 and calcium (Ca) = 8 ± 2 mmol/kg dry weight under resting conditions. Intracellular potassium content increased after exercise compared to resting values. There was a good correlation between exercise intensity, plasma potassium concentration and shifts in plasma volume, indicated by alterations in TPP. This probably reflects the very fast shift of potassium and fluid between muscle and plasma. Plasma potassium concentrations decreased below resting values post exercise. The higher dehydration degree and potassium sweat loss after exercise at 35°C was not reflected in lower muscular potassium content, but by a lower plasma potassium/total plasma protein ratio after exercise, indicating less circulating

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05029.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryRadioactive microspheres were used to measure cardiac output and blood flow to most major tissues in 4 ponies at rest in thermoneutral (16°C/60% RH) and mildly hot (41°C/34% RH) environments. In response to heat stress there were increases in cardiac output (2‐fold), respiratory frequency (5‐fold), blood flow to the skin of the body (3‐fold), and limbs (50%), respiratory muscles (2‐fold) and the upper respiratory tract (3‐fold). Ponies were able to maintain body temperature in the hot environment by increasing blood flow to the tissues involved in heat dissipation, while blood flow to all other tissues remained stable. This was achieved by increasing the cardiac output without need for reduction of blood flow to ot

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05030.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryModification of a ventilated capsule technique for the measurement of sweating rate (SR) is described for application in an exercising horse. The plastic capsule was sealed against the coat of the horse. Dry air was blown through the capsule over the skin and the change in absolute humidity (g/m3) between air entering and leaving the capsule was used to calculate SR. The effect of flow rate on the response characteristics of the system was investigated and measured over a range of sweating rates in a group of horses completing a short exercise test. Repeatability of SR measurements made at 2 sites, one 10 cm distal to thetuber sacrale(SRS) and the other approximately overlying C4 in the neck (SRN), were compared.To encourage the rapid and complete evaporation of moisture from the area of coat enclosed by the SR capsule, it was demonstrated that the degree of saturation of the air leaving the capsule should be maintained below 15% relative humidity (RH). This was best achieved at flow rates exceeding 35 l/min. No significant difference was found between the 2 repeated tests separated by 3 days, with respect to right atrial temperature (TRA) and SR. The modified system for the measurement of SR in the exercising horse used in this study was shown to be fast responding and capable of measuring a wide range of sweating rates. A good seal was maintained throughout and the capsule was removed without causing damage to the coat.

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05031.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe objectives of this study were to: 1) determine incremental and total sweat fluid and ion losses during and following (a) exercise training and (b) a treadmill Speed and Endurance exercise test (SEET) which simulated running speeds and distances required for each phase of an Olympic level (CCI****) 3‐day‐event in cool and hot ambient conditions and 2) determine the requirement for ion supplementation based on the calculated ion losses associated with these activities. Six exercise‐trained Thoroughbred horses completed 2 weeks of exercise training in each of 2 ambient conditions: cool, dry (CD, room temperature [T] = 20–22°C, relative humidity [RH]= 45–55%), or hot and humid (HH, T = 33–35°C, RH = 80–85%). Following the 2 week period of training in either CD or HH conditions, horses completed a SEET under similar conditions (either CD, or hot and dry (HD, T = 33–35°C, RH = 45–55%). Sweating rate and sweat ion composition for each 5 min interval was determined from sweat samples collected from a sealed pouch attached to the lateral thorax. Total sweat fluid losses during training in the heat were 2‐ or 3‐fold greater when compared to CD. Similarly, sweat fluid losses associated with the SEET in HD were almost double (19.2 litres) the losses in CD (11.7 litres). Total calculated ion losses associated with 2 h of training in HH (3724 mmol; 115.2 g) were significantly greater when compared to CD (1413 mmol; 43.5 g). Following the SEET and a 30 min recovery period, total ion losses in CD were 3636 mmol (112.2 g) compared with 6519 mmol (200.6 g) in HD. The differences in ion losses represent the increased sweating rates stimulated by higher core temperatures during moderate to high intensity exercise in warmer ambient conditions and increases in sweat ion concentrations associated with higher sweating rates. Extracellular fluid (ECF) ion losses during daily exercise training and the SEET were also calculated from changes in plasma ion concentrations and ECF volume. Calculated ECF ion losses were significantly higher in hot ambient conditions but were approximately 50% less than calculated sweat ion losses. The calculated sweat ion losses incurred during daily exercise training in hot and humid ambient conditions are>3‐fold higher than losses measured following exercise training in cooler conditions. Whereas fluid regulating hormones may have reduced urinary and faecal losses of ions during 2 weeks of training in HH, the quantity of sodium, potassium and chloride calculated to have been lost in sweat during the SEET in HD exceeded the daily dietary intake of these ions and suggests the need for appropriate ion supplementation during training and competition

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05032.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe objectives of this study were to: 1) determine the effects of heat and high relative humidity (RH) on the clinical and physiological responses of horses during and after daily exercise training and 2) determine whether repeated exposure to, and exercise in, the heat would result in improved thermal tolerance (heat acclimation). Six trained Thoroughbred horses completed 1 h of submaximal exercise in cool, dry conditions (CD) and during a daily 4 h period of exposure to high heat and humidity (HH, room temperature = 33–35°C, RH = 80–85%) for 22 days. Rectal temperature (Tre) and heart rate (HR) were measured before, during and after exercise and respiratory rate (RR) was measured before exercise and during a 2 h recovery. In HH, the rate of rise in Trewas significantly higher than in CD. However, by HH Day 5, Trebefore, during and after exercise was significantly lower than on HH Day 1. The day‐to‐day decrease in Treduring exercise was reflected in significant decreases in heat storage following exercise by HH Day 10 (910 ± 47 kcal) when compared to HH Day 1 (1211 ± 75 kcal). At rest, RR was initially higher in HH than CD, and a further increase in pre‐exercise RR from HH Day 1 to Day 10 may have contributed to the lower pre‐exercise Tre. Recovery RR was higher after HH Day 1 and was associated with a lower end‐of‐exercise Treand reduced heat storage by HH Day 5. Pre‐exercise HR did not change in the 1 h before exercise in CD and did not differ from HH Days 1–22. By HH Day 10, mean HR during the latter part of exercise was lower than HH Day 1 and was not different from pre‐exercise by 60 min of recovery. Pre‐exercise body mass did not change during the 3 wk period, and the decrease in body mass that occurred during the 4 h training period was significantly attenuated by HH Day 15 (9.8 ± 0.8 kg) when compared to HH Day 1 (12.5 ± 0.8 kg). Over the 3 week period of HH, mean 24 h water consumption increased from 26.0 ± 2.1 litres to 39.5 ± 3.2 litres, largely reflecting a 2‐fold increase in water intake during the 4 h period of heat exposure. It is concluded that 3 weeks of daily exposure to, and exercise in, hot and humid ambient conditions resulted in a progressive reduction in thermal and cardiovascular strain. Furthermore, the reported physiological adaptations are consistent with an improved ther

ISSN:0425-1644    

DOI:10.1111/j.2042-3306.1996.tb05033.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY