scholarly journals Core Temperature and Metabolic Responses After Carbohydrate Intake During Exercise at 30°C

2008 ◽  
Vol 43 (6) ◽  
pp. 585-591 ◽  
Author(s):  
Craig A. Horswill ◽  
John R. Stofan ◽  
Shannon C. Lovett ◽  
Chris Hannasch
Keyword(s):  
Steady State ◽  
Metabolic Rate ◽  
Core Temperature ◽  
Rectal Temperature ◽  
Repeated Measures ◽  
Sweat Rate ◽  
Fluid Replacement ◽  
Metabolic Responses ◽  
Hydration Status ◽  
Carbohydrate Ingestion

Abstract Context: Carbohydrate ingestion has recently been associated with elevated core temperature during exercise in the heat when testing for ergogenic effects. Whether the association holds when metabolic rate is controlled is unclear. Such an effect would have undesirable consequences for the safety of the athlete. Objective: To examine whether ingesting fluids containing carbohydrate contributed to an accelerated rise in core temperature and greater overall body heat production during 1 hour of exercise at 30°C when the effort was maintained at steady state. Design: Crossover design (repeated measures) in randomized order of treatments of drinking fluids with carbohydrate and electrolytes (CHO) or flavored-water placebo with electrolytes (PLA). The beverages were identical except for the carbohydrate content: CHO  =  93.7 ± 11.2 g, PLA  =  0 g. Setting: Research laboratory. Patients or Other Participants: Nine physically fit, endurance-trained adult males. Intervention(s): Using rectal temperature sensors, we measured core temperature during 30 minutes of rest and 60 minutes of exercise at 65% of maximal oxygen uptake (V˙o2 max) in the heat (30.6°C, 51.8% relative humidity). Participants drank equal volumes (1.6 L) of 2 beverages in aliquots 30 minutes before and every 15 minutes during exercise. Volumes were fixed to approximate sweat rates and minimize dehydration. Main Outcome Measure(s): Rectal temperature and metabolic response (V˙o2, heart rate). Results: Peak temperature, rate of temperature increase, and metabolic responses did not differ between beverage treatments. Initial hydration status, sweat rate, and fluid replacement were also not different between trials, as planned. Conclusions: Ingestion of carbohydrate in fluid volumes that minimized dehydration during 1 hour of steady-state exercise at 30°C did not elicit an increase in metabolic rate or core temperature.

scholarly journals Movement Technique and Standing Balance After Graded Exercise-Induced Dehydration

2021 ◽  
Vol 56 (2) ◽  
pp. 203-210
Author(s):  
William M. Adams ◽  
Samantha E. Scarneo-Miller ◽  
Lesley W. Vandermark ◽  
Luke N. Belval ◽  
Lindsay J. DiStefano ◽  
...  
Keyword(s):  
Postural Control ◽  
Repeated Measures ◽  
Scoring System ◽  
Neuromuscular Control ◽  
Fluid Replacement ◽  
Hydration Status ◽  
Hot Environment ◽  
Graded Exercise ◽  
Exercise Induced ◽  
Hot Environments

Context Hypohydration has been shown to alter neuromuscular function. However, the longevity of these impairments remains unclear. Objective To examine the effects of graded exercise-induced dehydration on neuromuscular control 24 hours after exercise-induced hypohydration. Design Crossover study. Setting Laboratory. Patients or Other Participants A total of 23 men (age = 21 ± 2 years, height = 179.8 ± 6.4 cm, mass = 75.24 ± 7.93 kg, maximal oxygen uptake [VO2max] = 51.7 ± 5.5 mL·kg−1·min−1, body fat = 14.2% ± 4.6%). Intervention(s) Participants completed 3 randomized exercise trials: euhydrated arrival plus fluid replacement (EUR), euhydrated arrival plus no fluid (EUD), and hypohydrated arrival plus no fluid (HYD) in hot conditions (ambient temperature = 35.2°C ± 0.6°C, relative humidity = 31.3% ± 2.5%). Each trial consisted of 180 minutes of exercise (six 30-minute cycles: 8 minutes at 40% VO2max; 8 minutes, 60% VO2max; 8 minutes, 40% VO2max; 6 minutes, passive rest) followed by 60 minutes of passive recovery. Main Outcome Measure(s) We used the Landing Error Scoring System and Balance Error Scoring System (BESS) to measure movement technique and postural control at pre-exercise, postexercise and passive rest (POSTEX), and 24 hours postexercise (POST24). Differences were assessed using separate mixed-design (trial × time) repeated-measures analyses of variance. Results The magnitude of hypohydration at POSTEX was different among EUR, EUD, and HYD trials (0.2% ± 1%, 3.5% ± 1%, and 5% ± 0.9%, respectively; P < .05). We observed no differences in Landing Error Scoring System scores at pre-exercise (2.9 ± 1.6, 3.0 ± 2.1, 3.0 ± 2.0), POSTEX (3.3 ± 1.5, 3.0 ± 2.0, 3.1 ± 1.9), or POST24 (3.3 ± 1.9, 3.2 ± 1.4, 3.3 ± 1.6) among the EUD, EUR, and HYD trials, respectively (P = .90). Hydration status did not affect BESS scores (P = .11), but BESS scores at POSTEX (10.4 ± 1.1) were greater than at POST24 (7.7 ± 0.9; P = .03). Conclusions Whereas exercise-induced dehydration up to 5% body mass did not impair movement technique or postural control 24 hours after a prolonged bout of exercise in a hot environment, postural control was impaired at 60 minutes after prolonged exercise in the heat. Consideration of the length of recovery time between bouts of exercise in hot environments is warranted.

Thermoregulatory responses to central injections of excess calcium in monkeys

1983 ◽  
Vol 245 (1) ◽  
pp. R76-R82
Author(s):  
C. V. Gisolfi ◽  
P. T. Wall ◽  
W. R. Mitchell
Keyword(s):  
Heart Rate ◽  
Metabolic Rate ◽  
Core Temperature ◽  
Sweat Rate ◽  
Cerebral Ventricles ◽  
General Body ◽  
Excess Calcium ◽  
Artificial Cerebrospinal Fluid ◽  
Average Skin ◽  
Skin Temperatures

In unanesthetized monkeys (4-8 kg), artificial cerebrospinal fluid (ACSF) containing excess (greater than 1.3 mM) amounts of Ca2+ was infused at 20 microliters/min for 5 min into the cerebral ventricles. Core and skin temperatures, respiratory gas exchange, heart rate, and sweat rate were monitored. At 22 degrees C, intracerebroventricular infusions of 13-39 mM Ca2+ produced a dose-related hypothermia associated with a dose-related fall in metabolic rate and heart rate and a rise in average skin temperature. General body sweating was not initiated, and respiratory water loss was unaffected; however, exercise activated sweating and elevated it from 0.05 to 0.22 mg X (cm2 X min)-1. At 35 or 40 degrees C, infusion of 26 mM Ca2+ failed to influence ongoing general body sweating; however, subsequent exercise increased sweat rate by 63%. Heart rate was unaffected. At 15 degrees C metabolic rate increased 50%. After infusing 26 mM Ca2+, metabolism decreased 6% and core temperature declined 0.8 +/- 0.24 degrees C. Skin temperatures continued to fall, heart rate fell, and sweating was not initiated. In contrast, infusing ACSF increased metabolism 11% and core temperature fell only 0.18 +/- 0.14 degrees C. The inability of exogenous Ca2+ to 1) initiate sweating at 22 degrees C, 2) elicit vasodilation at 15 degrees C, 3) initiate or stimulate sweating at 35 or 40 degrees C, or 4) lower core temperature at 35 or 40 degrees C argues against a set-point function for this cation.

Sweating response in cattle and its relation to rectal temperature, tolerance of sun and metabolic rate

1982 ◽  
Vol 99 (3) ◽  
pp. 479-487 ◽  
Author(s):  
Virginia A. Finch ◽  
I. L. Bennett ◽  
C. R. Holmes
Keyword(s):  
Metabolic Rate ◽  
Rectal Temperature ◽  
Sweat Rate ◽  
Temperature Tolerance ◽  
The Sun ◽  
Metabolic Potential ◽  
Linear Slope ◽  
Relationship Of ◽  
The Relationship ◽  
Good Heat

SUMMARYSweating rates were analysed in relation to rectal temperatures of cattle to yield a measure of sweating response within and between animals. The measurements, performed over 36 days, were done in a natural radiant environment on six steers in each of three breeds, Brahman (B), Brahman × Hereford–Shorthorn cross-breds (BX), and Shorthorn (S). Each steer was recorded for 30 min on six occasions randomly distributed among 6 h between 08.00 and 13.00 h, and on six occasions between 11.00 and 16.00 h, all on different days. Sweating response, e.g. the linear slope of the relationship between sweat rate and rectal temperature, was greater for B (294 g/m2. h/°C) than for BX (146 g/m2.h/°C) or S (194 g/m2.h/°C) which did not differ; this helped to explain why the range and mean rectal temperature in B were lower and little affected by environmental heat. Curvilinear models of the sweating response indicated that in the environmental conditions of this study, the limit of sweating for B and BX was not reached, while for S, the sweating response approached a plateau. Between animals, the relationship of sweating response to mean rectal temperature was negative (P < 0·01) and its relationship to the time spent in the sun at pasture positive (P < 0·025). Thus this measure of sweating response was a good indicator of thermoregulatory ability of the cattle. However, the sweating response of the steers did not relate to their grazing time or growth. The reasons for this are discussed. Finally, the sweating response was found to be negatively correlated with metabolic rate between animals within breeds (P < 0·01) and this suggested that it may be difficult to combine the desirable traits of good heat adaptation and high metabolic potential in cattle.

scholarly journals Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners

Nutrients ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 1374
Author(s):  
Juthamard Surapongchai ◽  
Vitoon Saengsirisuwan ◽  
Ian Rollo ◽  
Rebecca K. Randell ◽  
Kanpiraya Nithitsuttibuta ◽  
...  
Keyword(s):  
Fluid Intake ◽  
Sweat Rate ◽  
Statistical Significance ◽  
Sodium Concentration ◽  
Fluid Replacement ◽  
Whole Body ◽  
Hydration Status ◽  
P Value ◽  
Sweat Sodium Concentration ◽  
Sweat Sodium

Aim: The purpose of this study was to evaluate hydration status, fluid intake, sweat rate, and sweat sodium concentration in recreational tropical native runners. Methods: A total of 102 males and 64 females participated in this study. Participants ran at their self-selected pace for 30–100 min. Age, environmental conditions, running profiles, sweat rates, and sweat sodium data were recorded. Differences in age, running duration, distance and pace, and physiological changes between sexes were analysed. A p-value cut-off of 0.05 depicted statistical significance. Results: Males had lower relative fluid intake (6 ± 6 vs. 8 ± 7 mL·kg−1·h−1, p < 0.05) and greater relative fluid balance deficit (−13 ± 8 mL·kg−1·h−1 vs. −8 ± 7 mL·kg−1·h−1, p < 0.05) than females. Males had higher whole-body sweat rates (1.3 ± 0.5 L·h−1 vs. 0.9 ± 0.3 L·h−1, p < 0.05) than females. Mean rates of sweat sodium loss (54 ± 27 vs. 39 ± 22 mmol·h−1) were higher in males than females (p < 0.05). Conclusions: The sweat profile and composition in tropical native runners are similar to reported values in the literature. The current fluid replacement guidelines pertaining to volume and electrolyte replacement are applicable to tropical native runners.

Effects of Hydration on Febrile Temperature Patterns in Rabbits

2001 ◽  
Vol 2 (4) ◽  
pp. 277-291 ◽  
Author(s):  
Charlotte A. Richmond
Keyword(s):  
Heart Rate ◽  
Body Temperature ◽  
Core Temperature ◽  
Cardiovascular Responses ◽  
Fluid Replacement ◽  
Body Core Temperature ◽  
Hydration Status ◽  
Beneficial Role ◽  
Fluid Supplementation ◽  
Body Core

Patients with fever have a predisposition to experience dehydration, which may alter their thermoregulatory responses to elevated body temperature. In view of the recent discovery of the antipyretic activity of arginine vasopressin (AVP), it is possible that dehydration has a beneficial role during fever. Dehydration may enhance endogenous antipyresis by stimulating AVP release, making aggressive fluid replacement, which may inhibit AVP release, undesirable during fever. This study addressed the effects of manipulation of hydration status on temperature and cardiovascular responses in endotoxin-injected rabbits. Eight unanesthetized chronically instrumented rabbits were exposed to lipopolysaccharide (LPS) while in euhydrated state, after furosemide (5 mg/kg) and 24 hours of water deprivation (dehydrated), after infusion of saline (30 mL/kg) while in euhydrated state (hyperhydrated), and after saline (mL/per overnight body weight loss in grams) while in dehydrated state (rehydrated). Dehydrated rabbits display higher fevers that are biphasic in nature and are accompanied by increased vasoconstriction and duration of mean arterial pressure increases, indicating that activation of antipyretic mechanisms in dehydrated rabbits was not sufficient to reduce body core temperature. In addition, fluid supplementation in euhydrated rabbits did not alter the febrile response; however, a marked decrease in heart rate was noted. Furthermore, fluid supplementation in dehydrated rabbits significantly attenuates the rectal temperature and heart rate response to LPS injection, indicating the possibility that activation of antipyretic mechanisms of AVP in rehydrated rabbits was sufficient to reduce body core temperature. The results suggest that fluid supplementation has a beneficial role in keeping body temperature lower.

scholarly journals Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat

2017 ◽  
Vol 122 (1) ◽  
pp. 142-152 ◽  
Author(s):  
Matthew A. Tucker ◽  
Aaron R. Caldwell ◽  
Cory L. Butts ◽  
Forrest B. Robinson ◽  
Haley C. Reynebeau ◽  
...  
Keyword(s):  
Heat Stress ◽  
Body Fat ◽  
Rectal Temperature ◽  
Sweat Rate ◽  
Core Body Temperature ◽  
Hydration Status ◽  
High Body ◽  
Thermoregulatory Responses ◽  
Heat Production Rate ◽  
Local Sweat Rate

It is unclear whether men with low body fat (LO-BF) have impaired thermoregulation during exercise heat stress compared with those with high body fat (HI-BF) when euhydration (EU) is maintained. Furthermore, in LO-BF individuals, hypohydration (HY) impairs thermoregulatory responses during exercise heat stress, but it is unknown whether this occurs in HI-BF counterparts. The purpose of this study was to test the hypotheses that men with HI-BF have impaired thermoregulatory responses to exercise heat stress and that HY further exacerbates these impairments vs. LO-BF. Men with LO-BF [ n = 11, body mass (BM) 73.9 ± 8.5 kg, BF% 13.6 ± 3.8] and HI-BF ( n = 9, BM 89.6 ± 6.9 kg, BF% 30.2 ± 4.1), in a randomized crossover design, performed 60 min of upright cycling in a hot environment (40.3 ± 0.4°C, relative humidity 32.5 ± 1.9%) at a metabolic heat production rate of 6 W/kg BM and finished exercise either euhydrated (EU; 0.3 ± 1.2 vs. 0.3 ± 0.9% BM loss) or HY (−2.5 ± 1.1 vs. −1.7 ± 1.5% BM loss). Changes in rectal temperature (ΔTrec), local sweat rate (ΔLSR), and cutaneous vascular conductance (ΔCVC; %max) were measured throughout. When EU, LO-BF and HI-BF had similar CVC and LSR responses ( P > 0.05); however, LO-BF had a lower ΔTrec vs. HI-BF (0.92 ± 0.35 vs. 1.31 ± 0.32°C, P = 0.021). Compared with EU, HY increased end-exercise ΔTrec in LO-BF (0.47 ± 0.37°C, P < 0.01) but not in HI-BF (−0.06 ± 0.29°C, P > 0.05). HY, compared with EU, did not affect ΔLSR and ΔCVC in either group ( P > 0.05). We conclude that, when euhydrated, men with HI-BF have a greater increase in Trec vs. LO-BF but similar CVC and LSR. HY exacerbates increases in Trec in LO-BF but not HI-BF. NEW & NOTEWORTHY This is the first known investigation to compare thermoregulatory responses to exercise heat stress between men with high and low body fat (BF) in a physiologically uncompensable environment while simultaneously examining the confounding influence of hydration status. Both groups demonstrated similar sweating and cutaneous vasodilatory responses when euhydrated, despite vast differences in rectal temperature. Furthermore, in contrast to low BF, individuals with high BF demonstrated similar increases in core body temperature when either euhydrated or hypohydrated.

Core Temperature Responses to Elite Racewalking Competition

2020 ◽  
Vol 15 (6) ◽  
pp. 892-895 ◽  
Author(s):  
Christopher John Stevens ◽  
Megan L. Ross ◽  
Julien D. Périard ◽  
Brent S. Vallance ◽  
Louise M. Burke
Keyword(s):  
Steady State ◽  
Core Temperature ◽  
Rectal Temperature ◽  
Cold Water ◽  
International Association ◽  
Water Immersion ◽  
Heat Illness ◽  
Cooling Strategies ◽  
Race 1 ◽  
Temperature Responses

Purpose: The core temperature responses during exercise and effects of different cooling strategies on endurance performance under heat stress have been investigated in recreational athletes. This investigation aimed to determine peak rectal temperatures during elite racewalking competitions and to detail any cooling strategies used. Methods: Rectal temperature was measured in 14 heat-adapted elite/preelite race walkers (9 females) via a telemetric capsule across 4 outdoor events, including the 2018 Commonwealth Games (race 1: 20 km, 25°C, 74% relative humidity [RH], n = 2) and 3 International Association of Athletics Federations–sanctioned 10-km events (race 2: 19°C, 34% RH, n = 2; race 3: 29°C, 47% RH, n = 14; and race 4: 23°C, 72% RH, n = 11). All athletes completed race 3, and a subsample completed the other events. Their use of cooling strategies and symptoms of heat illness were determined. Results: Peak rectal temperatures >40°C were observed in all events. The highest rectal temperature observed during an event was 41.2°C. These high rectal temperatures were observed without concomitant heat illness, with the exception of cramping in one athlete during race 1. The rectal temperatures tended to reach a steady state in the second half of the 20-km event, but no steady state was observed in the 10-km events. The athletes used cooling strategies in race 1 only, implementing different combinations of cold-water immersion, ice-slurry ingestion, ice-towel application, ice-vest application, and facial water spraying. Conclusions: Elite/preelite race walkers experience rectal temperatures >40°C during competition despite only moderate-warm conditions, and even when precooling and midcooling strategies are applied.

scholarly journals MON-LB305 The “Normal” Hormonal Levels in Athletes: Should Reference Ranges Be Adapted for the Physically Active Population?

2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Flavio Cadegiani ◽  
Tatiana P C Abrao ◽  
Pedro Luiz H da Silva ◽  
Claudio E Kater
Keyword(s):  
Physical Activity ◽  
Metabolic Rate ◽  
Basal Metabolic Rate ◽  
Fat Oxidation ◽  
Metabolic Responses ◽  
Hydration Status ◽  
Reference Ranges ◽  
Physically Active ◽  
Overtraining Syndrome ◽  
Wide Range

Abstract Background:Despite the growing number of physically active subjects, including elite and amateur athletes, little is known regarding metabolic and hormonal chronic adaptations to exercises. While the elucidation of the hormonal and metabolic physiological adaptations to physical activity is of emerging importance, the Endocrine and Metabolic Responses on Overtraining Syndrome (EROS) study have serendipitously unveiled the existence of multiple metabolic and endocrine physiological changes in male athletes, including chronic increase of testosterone with concurrent physiological increase of estradiol, enhanced GH and cortisol responses to stimulations,andincreased catecholamines, basal metabolic rate, fat oxidation, and hydration status. These findings were uncovered due to a novel methodological design in which athletes affected by overtraining syndrome (OTS) were compared to a two control groups, of healthy athletes (ATL) and healthy non-physically active controls (NPAC). Since none of the parameters were directly dependent on exercise or performance, differences between these two groups were unexpected. From the fact that several parameters were shown to be different between ATL and NPAC, we realized that the use of the reference ranges for general population to analyze results in athletes may potentially under- and over-diagnose a wide range of conditions. Our objective is therefore to determine whether athletes should be biochemically evaluated through specific adapted ranges, and propose preliminary adaptations in these ranges. Methods: A systematic review on the literature on endocrine and metabolic adaptations to exercise was performed, as well as a thorough analysis of the seven arms of the Endocrine and Metabolic Responses on Overtraining Syndrome (EROS) study. Results:Multiple reference ranges were shown to be inaccurate for athletes. Among the parameters that should be adapted for athletes, and their respective adaptedranges include: 1. Cortisol response to an insulin stimulation test (ITT) (&gt; 20.5 μg/dL); 2. GH response to an ITT (&gt; 12 μg/L); 3. Prolactin response to an ITT (&gt; 22 ng/mL); 4. Salivary cortisol at 8AM (&gt; 450 ng/dL); 5. Total testosterone (&gt; 450 ng/dL); 6. Estradiol (25-45 pg/mL) - and testosterone-to-estradiol ratio maintained &gt; 13.7; 7. Total nocturnal urinary catecholamines (&gt; 220 μg/12h); 8. Resting lactate (&lt; 1.0 nMol/L); 9. Measured-to-predicted basal metabolic rate (BMR) (&gt; 105%); 10. Fat oxidation (in relation to total BMR) (&gt; 50%); and 11. Hydration status (body water &gt; 62% of total body weight). Conclusion: Analysis of biochemical parameters in athleted should be interpreted with cautious, particularly hormonal and metabolic parameters, once many parameters likely undergo adaptive changes when under physical activity. Preliminary adaptations for the ranges have been proposed.

Exercise slightly above the maximal lactate steady state reduces self-efficacy and increases negative affect

2019 ◽  
Author(s):  
James Graeme Wrightson ◽  
Louis Passfield
Keyword(s):  
Steady State ◽  
Negative Affect ◽  
Power Output ◽  
Self Efficacy ◽  
Repeated Measures ◽  
Physiological State ◽  
Constant Load ◽  
Peak Power Output ◽  
Time To Exhaustion ◽  
Maximal Lactate Steady State

Objectives: To examine the effect of exercise at and slightly above the maximal lactate steady state (MLSS) on self-efficacy, affect and effort, and their associations with exercise tolerance.Design: Counterbalanced, repeated measures designMethod: Participants performed two 30‐minute constant‐load cycling exercise at a power output equal to that at MLSS and 10 W above MLSS, immediately followed by a time‐to‐exhaustion test at 80% of their peak power output. Self-efficacy, affect and effort were measured before and after 30 minutes of cycling at and above MLSS.Results: Negative affect and effort higher, and self-efficacy and time to exhaustion were reduced, following cycling at MLSS + 10 W compared to cycling at the MLSS. Following exercise at the MLSS self-efficacy, affect and effort were all associated with subsequent time-to exhaustion. However, following exercise at MLSS + 10 W, only affect was associated with time-to exhaustion. Conclusions: Self efficacy, affect and effort are profoundly affected by physiological state, highlighting the influence of somatic states on perceptions and emotions during exercise. The affective response to exercise appears to be associated with exercise tolerance, indicating that the emotional, as well as physiological, responses should be considered when prescribing exercise training.

Wetting and the physiological responses of grain-fed cattle in a heated environment

2004 ◽  
Vol 55 (3) ◽  
pp. 253 ◽  
Author(s):  
John B. Gaughan ◽  
M. Shane Davis ◽  
Terry L. Mader
Keyword(s):  
Heat Stress ◽  
Experimental Design ◽  
Rectal Temperature ◽  
Environmental Conditions ◽  
Dry Matter ◽  
Physiological Responses ◽  
Dry Matter Intake ◽  
Metabolic Responses ◽  
Hot Days ◽  
Carry Over

A controlled crossover experimental design was used to determine the effect of altered water sprinkling duration on heifers subjected to heat stress conditions. Heifers were subjected to 3 days of thermoneutral conditions followed by 3 days of hot conditions accompanied by water sprinkling between 1300 and 1500 h (HOT1–3). Then on the following 2 days (HOT4–5), environmental conditions remained similar, but 3 heifers were sprinkled between 1200 and 1600 h (WET) and 3 were not sprinkled (NONWET). This was followed by a 1-day period (HOT6) in which environmental conditions and sprinkling regimen were similar to HOT1–3. Rectal temperature (RT) was collected hourly, and respiration rate (RR) was monitored every 2 h on HOT Days 2, 4, 5, and 6. Dry matter intake and rate of eating were also determined. Sprinkling reduced RR and RT (P < 0.01) of all heifers during HOT1–3. During HOT4–5, WET heifers had lower (P < 0.05) RT than NONWET from 1300 to 700 h and lower RR from 1400 to 2000 h. Dry matter intake of NONWET heifers was reduced by 30.6% (P < 0.05) during HOT4–5 and by 51.2% on HOT6. On HOT4–5 the dry matter intakes of WET heifers were similar to intakes under thermoneutral conditions. During HOT6, RT was again reduced following sprinkling in all heifers. Comparison of RT and RR of NONWET and WET heifers on HOT1–3 v. HOT6 revealed that under similar environmental conditions, NONWET heifers had increased RT, partially due to carry-over from HOT4–5. However, NONWET heifers had 40% lower feed intake but tended to have lower RR on HOT6 v. HOT1–3. Only RR of WET heifers was greater on HOT6, possibly a result of switching from a 4-h back to a 2-h sprinkling period, while maintaining a 62% greater intake (5.80 v. 3.58 kg/day) than NONWET heifers during this time. Results suggest that inconsistent cooling regimens may increase the susceptibility of cattle to heat stress and elicit different physiological and metabolic responses.

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