scholarly journals PSIX-26 Effect of supplemental Arg on respiration rate and body temperature of pigs exposed to heat stress

2019 ◽  
Vol 97 (Supplement_3) ◽  
pp. 351-351
Author(s):  
Adriana Morales Trejo ◽  
Fernanda González ◽  
Hugo Bernal ◽  
Miguel Cervantes ◽  
Caroline Gonzalez-Vega ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Heat Stress ◽  
Data Analysis ◽  
Body Temperature ◽  
Ambient Temperature ◽  
Respiration Rate ◽  
Feed Intake ◽  
Well Being ◽  
Period 2 ◽  
Body Heat

Abstract Heat stress (HS) reduces feed intake and affects the well-being of pigs by increasing their body temperature (BT) and respiration rate (RR). Nitric oxide, an Arg metabolite, helps to dissipate body heat by stimulating blood vasodilation. Because reduced feed intake translates into decreased Arg consumption, the effect of supplementing Arg in the diet on BT and RR was analyzed using 8-ileal cannulated pigs (61.7±2.7 kg BW) exposed to HS. A thermometer set to register BT at 5-min intervals was implanted into the ileum. There were two treatments: control wheat-soybean meal plus free Lys-Thr diet (CON), and the CON diet added with 0.20% free Arg (ARG). The study was conducted in two-6 d periods; d1-d3 for diet adaptation and d4-d6 for BT data analysis. The RR (respirations per min - rpm) was measured in all pigs at 0600-h and 1600-h. Pigs were fed at 0700-h and 1900-h, 900 g/meal. Ambient temperature and relative humidity were: 28.2-to-34.6 °C, 53-to-82%, respectively. Ambient temperature and BT followed a similar pattern every day. There was no interaction in BT and RR between periods. Overall, BT of ARG pigs (40.75°C) was slightly lower (P < 0.05) than in CON pigs (40.71°C). Arg supplementation greatly reduced RR (rpm) regardless of period and day time (P < 0.05): overall (91, 73), period-1 (98, 78), period-2 (85, 68), 0600-h, (68, 52), 1600-h (115, 94), respectively. The RR at 0600-h (60) was lower than at 1400-h (109; P < 0.05) regardless of diet. The reduced RR because of Arg supplementation may be explained as an increased synthesis of nitric oxide probably resulting in both increased vasodilation and dissipation of body heat. In conclusion, although supplemental Arg caused a modest decrease in BT, the large RR reduction may indicate that Arg might help to improve the welfare of HS pigs.

scholarly journals 172 Feed intake level and ambient temperature affect the body temperature of pigs exposed to heat stress.

2018 ◽  
Vol 96 (suppl_3) ◽  
pp. 295-296
Author(s):  
A Morales Trejo ◽  
D Antoine ◽  
A Valle-Fimbres ◽  
H Bernal Barragán ◽  
L Camacho ◽  
...  
Keyword(s):  
Heat Stress ◽  
Body Temperature ◽  
Ambient Temperature ◽  
Feed Intake ◽  
The Body ◽  
Intake Level

SUMMER WATER CONSUMPTION, BODY TEMPERATURE AND RESPIRATION RATE IN LAMBS

1976 ◽  
Vol 56 (4) ◽  
pp. 739-744 ◽  
Author(s):  
WILLIAM HOHENBOKEN ◽  
THEODORE P. KISTNER
Keyword(s):  
Body Temperature ◽  
Ambient Temperature ◽  
Respiration Rate ◽  
Water Intake ◽  
Water Consumption ◽  
Feed Intake ◽  
Feed Water ◽  
Body Temperature Change ◽  
Feedlot Lambs ◽  
Maximum Minimum

The effects of time on feed and of ambient temperature on water intake, and the effects of preconditioning and shearing treatments and of ambient temperature on body temperature and respiration rate of feedlot lambs were examined. Daily ambient temperature maximum, minimum and range averaged 27.5, 10.8 and 16.7 C, respectively, for 56 days between July and September. For the first 24 days that the lambs were on feed, water intake was not affected by ambient temperature. Intake did increase linearly with day (b = 160 ml), concurrently with increasing feed intake. During the remaining 32 days, water intake per lamb increased 139 ml per 1 C rise in average daily ambient temperature. Afternoon body temperature, morning to afternoon body temperature change, and respiration rate all increased with increasing ambient temperature. Preconditioning 1 wk before weaning (pneumonia, ovine ecthyma and enterotoxemia vaccinations and drenching for tapeworms, intestinal roundworms and coccidia) vs. conditioning the lambs with the same treatments at the time of weaning and shipment did not affect body temperature or respiration rate. Lambs sheared with a clipper attachment which left a 1-cm fleece stubble averaged 0.3 C lower in afternoon body temperature than either close-shorn or unshorn lambs.

scholarly journals Endophytes and heat tolerance in lambs grazing perennial ryegrass

1994 ◽  
pp. 265-270 ◽  
Author(s):  
L.R. Fletcher ◽  
L.J. Markham ◽  
S.R. White
Keyword(s):  
Heat Stress ◽  
Body Temperature ◽  
Ambient Temperature ◽  
Respiration Rate ◽  
Perennial Ryegrass ◽  
Respiration Rates ◽  
Low Concentrations ◽  
Free Treatment ◽  
Significant Difference ◽  
Adverse Affects

Endophytes in perennial ryegrass protect their hosts against attack by Argentine stem weevil but cause adverse affects, including heat stress, in grazing animals. Ten lambs were grazed on Grasslands Nui ryegrass without endophyte or with its wildtype or a high ergovaline-producing endophyte (196). Five lambs from the 196 treatment were swapped for 5 on the endophyte-free treatment after 20 days. Rectal temperatures and respiration rates were measured daily; on one day they were measured every 2-4 hours. There was a significant difference in respiration rate and body temperature between lambs grazing endophyte and endophytefree treatments but not between the two endophyte treatments. There was no interaction with ambient temperature within the range 12-30°C. When lambs where transferred from toxic to non-toxic treatments there was no significant decrease in body temperature or respiration rate witbin 14 days. Ergovaline, even at low concentrations, affects thermo-regulation in lambs and is undesirable in perennial ryegrasslendophyte associationsEndophytes in perennial ryegrass protect their hosts against attack by Argentine stem weevil but cause adverse affects, including heat stress, in grazing animals. Ten lambs were grazed on Grasslands Nui ryegrass without endophyte or with its wildtype or a high ergovaline-producing endophyte (196). Five lambs from the 196 treatment were swapped for 5 on the endophyte-free treatment after 20 days. Rectal temperatures and respiration rates were measured daily; on one day they were measured every 2-4 hours. There was a significant difference in respiration rate and body temperature between lambs grazing endophyte and endophytefree treatments but not between the two endophyte treatments. There was no interaction with ambient temperature within the range 12-30°C. When lambs where transferred from toxic to non-toxic treatments there was no significant decrease in body temperature or respiration rate witbin 14 days. Ergovaline, even at low concentrations, affects thermo-regulation in lambs and is undesirable in perennial ryegrass endophyte associations. Keywords: body temperature, endophyte,ergovaline, heat stress, Lolium perenne, respiration rate

scholarly journals Heat Stress and Cardiovascular, Hormonal, and Heat Shock Proteins in Humans

2012 ◽  
Vol 47 (2) ◽  
pp. 184-190 ◽  
Author(s):  
Masaki Iguchi ◽  
Andrew E. Littmann ◽  
Shuo-Hsiu Chang ◽  
Lydia A. Wester ◽  
Jane S. Knipper ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heat Stress ◽  
Heat Shock ◽  
Body Temperature ◽  
Controlled Trial ◽  
Whole Body ◽  
Cord Injury ◽  
Whole Body Heat Stress ◽  
Body Heat

Context: Conditions such as osteoarthritis, obesity, and spinal cord injury limit the ability of patients to exercise, preventing them from experiencing many well-documented physiologic stressors. Recent evidence indicates that some of these stressors might derive from exercise-induced body temperature increases. Objective: To determine whether whole-body heat stress without exercise triggers cardiovascular, hormonal, and extra-cellular protein responses of exercise. Design: Randomized controlled trial. Setting: University research laboratory. Patients or Other Participants: Twenty-five young, healthy adults (13 men, 12 women; age = 22.1 ± 2.4 years, height = 175.2 ± 11.6 cm, mass = 69.4 ± 14.8 kg, body mass index = 22.6 ± 4.0) volunteered. Intervention(s): Participants sat in a heat stress chamber with heat (73°C) and without heat (26°C) stress for 30 minutes on separate days. We obtained blood samples from a subset of 13 participants (7 men, 6 women) before and after exposure to heat stress. Main Outcome Measure(s): Extracellular heat shock protein (HSP72) and catecholamine plasma concentration, heart rate, blood pressure, and heat perception. Results: After 30 minutes of heat stress, body temperature measured via rectal sensor increased by 0.8°C. Heart rate increased linearly to 131.4 ± 22.4 beats per minute (F6,24 = 186, P < .001) and systolic and diastolic blood pressure decreased by 16 mm Hg (F6,24 = 10.1, P < .001) and 5 mm Hg (F6,24 = 5.4, P < .001), respectively. Norepinephrine (F1,12 = 12.1, P = .004) and prolactin (F1,12 = 30.2, P < .001) increased in the plasma (58% and 285%, respectively) (P < .05). The HSP72 (F1,12 = 44.7, P < .001) level increased with heat stress by 48.7% ± 53.9%. No cardiovascular or blood variables showed changes during the control trials (quiet sitting in the heat chamber with no heat stress), resulting in differences between heat and control trials. Conclusions: We found that whole-body heat stress triggers some of the physiologic responses observed with exercise. Future studies are necessary to investigate whether carefully prescribed heat stress constitutes a method to augment or supplement exercise.

scholarly journals Roles of nitric oxide synthase isoforms in cutaneous vasodilation induced by local warming of the skin and whole body heat stress in humans

2009 ◽  
Vol 107 (5) ◽  
pp. 1438-1444 ◽  
Author(s):  
Dean L. Kellogg ◽  
Joan L. Zhao ◽  
Yubo Wu
Keyword(s):  
Nitric Oxide ◽  
Heat Stress ◽  
No Synthase ◽  
Whole Body ◽  
Doppler Flowmetry ◽  
Vasodilator Response ◽  
Cutaneous Vasodilation ◽  
Forearm Skin ◽  
Whole Body Heat Stress ◽  
Body Heat

Nitric oxide (NO) participates in the cutaneous vasodilation caused by increased local skin temperature (Tloc) and whole body heat stress in humans. In forearm skin, endothelial NO synthase (eNOS) participates in vasodilation due to elevated Tloc and neuronal NO synthase (nNOS) participates in vasodilation due to heat stress. To explore the relative roles and interactions of these isoforms, we examined the effects of a relatively specific eNOS inhibitor, Nω-amino-l-arginine (LNAA), and a specific nNOS inhibitor, Nω-propyl-l-arginine (NPLA), both separately and in combination, on skin blood flow (SkBF) responses to increased Tloc and heat stress in two protocols. In each protocol, SkBF was monitored by laser-Doppler flowmetry (LDF) and mean arterial pressure (MAP) by Finapres. Cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). Intradermal microdialysis was used to treat one site with 5 mM LNAA, another with 5 mM NPLA, a third with combined 5 mM LNAA and 5 mM NPLA (Mix), and a fourth site with Ringer only. In protocol 1, Tloc was controlled with combined LDF/local heating units. Tloc was increased from 34°C to 41.5°C to cause local vasodilation. In protocol 2, after a period of normothermia, whole body heat stress was induced (water-perfused suits). At the end of each protocol, all sites were perfused with 58 mM nitroprusside to effect maximal vasodilation for data normalization. In protocol 1, at Tloc = 34°C, CVC did not differ between sites ( P > 0.05). LNAA and Mix attenuated CVC increases at Tloc = 41.5°C to similar extents ( P < 0.05, LNAA or Mix vs. untreated or NPLA). In protocol 2, in normothermia, CVC did not differ between sites ( P > 0.05). During heat stress, NPLA and Mix attenuated CVC increases to similar extents, but no significant attenuation occurred with LNAA ( P < 0.05, NPLA or Mix vs. untreated or LNAA). In forearm skin, eNOS mediates the vasodilator response to increased Tloc and nNOS mediates the vasodilator response to heat stress. The two isoforms do not appear to interact during either response.

scholarly journals 262 Heat stress alleviation and dynamic temperature measurement for growing beef cattle

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 192-193
Author(s):  
Sheyenne M Augenstein ◽  
Meredith A Harrison ◽  
Sarah C Klopatek ◽  
James W Oltjen
Keyword(s):  
Heat Stress ◽  
Body Temperature ◽  
Beef Cattle ◽  
Ambient Temperature ◽  
The Body ◽  
Control Group ◽  
Temperature Threshold ◽  
Sprinkler Systems ◽  
Significant Difference ◽  
The Impact

Abstract Heat stress continues to be a challenge for feedlot producers, forcing physiological adaptations in beef cattle that can have a negative impact on gain and carcass quality. Feedlots may want to incorporate systems that aid in mitigating heat stress, including sprinkler systems, which are commonly found on dairies. The objective of this study was to determine the impact of sprinkler systems on the body temperature of growing feedlot steers applied at three different temperature thresholds. Thirty-two Angus-cross beef steers (298 ± 15 SD days of age) were randomly assigned to 8 pens. Treatments were assigned to pens according to location to avoid drainage issues, with one replicate located on the eastern side of the feedlot and the other replicate located on the western side. Treatments including no sprinklers (C), high temperature threshold sprinklers (HT), moderate temperature threshold sprinklers (MT) or low temperature threshold sprinklers (LT). Sprinklers (flow rate: 5.11 L/min) were activated at 33°C (HT), 28°C (MT), and 23°C (LT) for five minutes at corresponding temperatures every thirty minutes for 57 days. Rectal temperature of steers in their pens was measured in the morning (0800 h), afternoon (1500 h), and evening (1900 h) three days each week (Monday, Wednesday, Friday) for a total of 19 experimental days. Weather measurements, including ambient temperature, windspeed, humidity and solar radiation were recorded at each measurement time along with the maximum values for each day. The change in body temperature (ΔBT) between the morning and afternoon was affected by ambient temperature (P &lt; 0.01); MT (P = 0.02) and LT (P = 0.02) – different than C. There was no significant difference between sprinkler treatments and the control group (P &gt; 0.05). Day affected (ΔBT) between the morning and afternoon (P &lt; 0.05) and the afternoon and evening (P &lt; 0.05). When averaged by day, the control group was significantly higher than MT (P = 0.04) between the morning and afternoon. The control group was also significantly higher than LT between the morning and afternoon (P = 0.03) and the afternoon and evening (P &lt; 0.01). The change in steer body temperature between afternoon and morning was affected by ambient temperature, and averaged across days, lowering the temperature threshold for sprinkling decreased in the afternoon and evening body temperature increase in steers.

scholarly journals Endothelial nitric oxide synthase control mechanisms in the cutaneous vasculature of humans in vivo

2008 ◽  
Vol 295 (1) ◽  
pp. H123-H129 ◽  
Author(s):  
Dean L. Kellogg ◽  
Joan L. Zhao ◽  
Yubo Wu
Keyword(s):  
Nitric Oxide ◽  
Heat Stress ◽  
Local Heating ◽  
Ringer Solution ◽  
Whole Body ◽  
Control Mechanisms ◽  
Local Skin ◽  
Doppler Flowmetry ◽  
Whole Body Heat Stress ◽  
Body Heat

Nitric oxide (NO) participates in locally mediated vasodilation induced by increased local skin temperature (Tloc) and in sympathetically mediated vasodilation during whole body heat stress. We hypothesized that endothelial NOS (eNOS) participates in the former, but not the latter, response. We tested this hypothesis by examining the effects of the eNOS antagonist NG-amino-l-arginine (l-NAA) on skin blood flow (SkBF) responses to increased Tloc and whole body heat stress. Microdialysis probes were inserted into forearm skin for drug delivery. One microdialysis site was perfused with l-NAA in Ringer solution and a second site with Ringer solution alone. SkBF [laser-Doppler flowmetry (LDF)] and blood pressure [mean arterial pressure (MAP)] were monitored, and cutaneous vascular conductance (CVC) was calculated (CVC = LDF ÷ MAP). In protocol 1, Tloc was controlled with LDF/local heating units. Tloc initially was held at 34°C and then increased to 41.5°C. In protocol 2, after a normothermic period, whole body heat stress was induced (water-perfused suits). At the end of both protocols, 58 mM sodium nitroprusside was perfused at both microdialysis sites to cause maximal vasodilation for data normalization. In protocol 1, CVC at 34°C Tloc did not differ between l-NAA-treated and untreated sites ( P > 0.05). Local skin warming to 41.5°C Tloc increased CVC at both sites. This response was attenuated at l-NAA-treated sites ( P < 0.05). In protocol 2, during normothermia, CVC did not differ between l-NAA-treated and untreated sites ( P > 0.05). During heat stress, CVC rose to similar levels at l-NAA-treated and untreated sites ( P > 0.05). We conclude that eNOS is predominantly responsible for NO generation in skin during responses to increased Tloc, but not during reflex responses to whole body heat stress.

scholarly journals Effects of chromium supplementation on physiology, feed intake, and insulin related metabolism in growing pigs subjected to heat stress

2017 ◽  
Vol 1 (1) ◽  
pp. 116-125 ◽  
Author(s):  
F. Liu ◽  
J. J. Cottrell ◽  
U. Wijesiriwardana ◽  
F. W. Kelly ◽  
S. S. Chauhan ◽  
...  
Keyword(s):  
Heat Stress ◽  
Insulin Sensitivity ◽  
Respiration Rate ◽  
Rectal Temperature ◽  
Feed Intake ◽  
Insulin Response ◽  
Thermal Exposure ◽  
Growing Pigs ◽  
Model Assessment ◽  
Intravenous Glucose

Abstract Improving insulin sensitivity may reduce impacts of heat stress (HS) in pigs by facilitating heat dissipation. Chromium (Cr) has been reported to improve insulin sensitivity in pigs. Therefore, the aim of this experiment was to investigate whether Cr supplementation can mitigate HS in growing pigs. Thirty-six gilts were randomly assigned to 2 diets containing 0 (control) or 400 ppb Cr. After 14 d the supplemented pigs were allocated to either 8 d thermoneutral (20°C constant; TN) or cyclic HS (35°C, 0900 h to 1700 h) conditions and continued their respective diet (n = 9 per group). Growth performance was recorded during the 14-d supplementation period. The physiological responses to HS were monitored by measuring respiration rate, rectal temperature, blood gas chemistry, and feed intake during thermal exposure. Kinetics of plasma glucose, insulin and NEFA were studied by intravenous glucose tolerance test (IVGTT) on d 8 of thermal treatment. Results showed Cr alleviated the HS-increased rectal temperature (P &lt; 0.05) and respiration rate (P &lt; 0.01) at 1300 h and 1600 h during thermal exposure. However, Cr did not mitigate the reduction in average daily feed intake which was reduced by 35% during HS or the HS-induced respiratory alkalosis. Chromium tended to increase average daily gain (0.86 vs. 0.95 kg, P = 0.070) during the 14-d supplementation under TN conditions before thermal exposure, which might be associated with the potential of Cr in improving overall insulin sensitivity, as evidenced by a reduced insulin resistance index calculated by Homeostatic Model Assessment (HOMA-IR; 0.65 vs. 0.51, P = 0.013) and a tendency of reduced fasting plasma insulin concentration (1.97 vs. 1.67 μU/mL, P = 0.094). Heat stress decreased the acute insulin releasing rate (P = 0.012) and consequently slowed glucose clearance rate (P = 0.035) during IVGTT. Besides, HS enlarged the values of area under the curve of NEFA during IVGTT (P &lt; 0.01), indicating a reduced lipid mobilization. In conclusion, HS reduced insulin response to IVGTT. Chromium supplementation exhibited a potential in improving insulin sensitivity and mitigating HS symptoms in growing pigs.

PREDICTION OF CLINICAL DIAGNOSTIC INDICATORS AND THE LEVEL OF MILK PRODUCTIVITY OF COWS

2021 ◽  
pp. 42-47
Author(s):  
Е.О. КРУПИН
Keyword(s):  
Heat Stress ◽  
Thermal Stress ◽  
Body Temperature ◽  
Dairy Cows ◽  
Milk Production ◽  
Respiration Rate ◽  
Average Increase ◽  
Milk Productivity ◽  
Humidity Index ◽  
Respiratory Movements

В различные синоптические сроки выявлено количество измерений по индексу температуры и влажности (ТВИ) в животноводческом помещении, при которых у коров наблюдается тепловой стресс. Спрогнозированы данные о температуре тела и частоте дыхания коров в условиях теплового стресса и его отсутствия, в том числе и по четырем срокам измерений. Определен потенциально возможный уровень молочной продуктивности коров при отсутствии теплового стресса. По методу E.C. Thom установлено, в среднем, 80,0% значений ТВИ, характеризующих условия среды как «тепловой стресс». Наблюдалось увеличение доли данных значений с 10 ч утра до 19 ч. По A. Berman et al. Выявлено, в среднем, 10,9% значений ТВИ, а по M.K. Yousef — 5,0%, относящихся к тепловому стрессу. В 15-й синоптический срок измерений по Гринвичу в животноводческом помещении спрогнозирована наибольшая вероятность теплового стресса. Среднее увеличение температуры тела коров с 6-го по 15-й синоптические сроки измерений при тепловом стрессе составит 1,0% (0,4°C, P<0,001), а частоты дыхания — 51,3% (18 дыхательных движений в 1 мин, (P<0,001). Максимальная динамика увеличения температуры тела наблюдается в 13 ч и 16 ч, а частоты дыхания — в 13 ч. Потенциальная молочная продуктивность дойных коров в летние месяцы может быть в среднем на 8,9% выше. In various synoptic terms in the cowshed room, the amount of measurements of the temperature of the heat and humidity index was revealed when the cows suffer from thermal stress. Data on body temperature and respiration rate of cows in conditions of heat stress and its absence were predicted, including those for four measurement periods. Potentially possible level of milk production of cows in the absence of heat stress was determined. According to E.C. Thom is found on average 80.0% of the values of THI, characterizing environmental conditions as "heat stress". An increase in the share of these values is observed in the period from 10:00 to 19:00. According to A. Berman et al. revealed on average 10.9% of THI values, and according to M.K. Yousef — 5.0% of the THI values related to heat stress. In 15, the synoptic term of measurements in Greenwich in the cowshed, the highest probability of heat stress is predicted. The average increase in body temperature of cows from 6 to 15 synoptic term of measurements in Greenwich heat stress will be 1.0% (0.4°C, P<0.001), and the respiration rate will be 51.3% (18 respiratory movements per minute, P<0.001). The maximum dynamics of an increase in body temperature is observed at 13:00 and 16:00 for body temperature, and respiratory rate at 13:00. The potential milk production of dairy cows in the summer months can be 8.9% higher on average.

scholarly journals Heat stress-induced deficits in growth, metabolic efficiency, and cardiovascular function coincided with chronic systemic inflammation and hypercatecholaminemia in ractopamine-supplemented feedlot lambs

2020 ◽  
Vol 98 (6) ◽  
Author(s):  
Rebecca M Swanson ◽  
Richard G Tait ◽  
Beth M Galles ◽  
Erin M Duffy ◽  
Ty B Schmidt ◽  
...  
Keyword(s):  
Heat Stress ◽  
Systemic Inflammation ◽  
Feed Intake ◽  
White Blood Cells ◽  
Well Being ◽  
Fat Content ◽  
Left Ventricular ◽  
Metabolic Efficiency ◽  
Feedlot Lambs ◽  
The Impact

Abstract Heat stress hinders growth and well-being in livestock, an effect that is perhaps exacerbated by the β1 agonist ractopamine. Heat stress deficits are mediated in part by reduced feed intake, but other mechanisms involved are less understood. Our objective was to determine the direct impact of heat stress on growth and well-being in ractopamine-supplemented feedlot lambs. Commercial wethers were fed under heat stress (40 °C) for 30 d, and controls (18 °C) were pair-fed. In a 2 × 2 factorial, lambs were also given a daily gavage of 0 or 60 mg ractopamine. Growth, metabolic, cardiovascular, and stress indicators were assessed throughout the study. At necropsy, 9th to 12th rib sections (four-rib), internal organs, and feet were assessed, and sartorius muscles were collected for ex vivo glucose metabolic studies. Heat stress increased (P &lt; 0.05) rectal temperatures and respiration rates throughout the study and reduced (P &lt; 0.05) weight gain and feed efficiency over the first week, ultrasonic loin-eye area and loin depth near the end of the study, and four-rib weight at necropsy. Fat content of the four-rib and loin were also reduced (P &lt; 0.05) by heat stress. Ractopamine increased (P &lt; 0.05) loin weight and fat content and partially moderated the impact of heat stress on rectal temperature and four-rib weight. Heat stress reduced (P &lt; 0.05) spleen weight, increased (P &lt; 0.05) adrenal and lung weights, and was associated with hoof wall overgrowth but not organ lesions. Ractopamine did not affect any measured indicators of well-being. Heat stress reduced (P &lt; 0.05) blood urea nitrogen and increased (P &lt; 0.05) circulating monocytes, granulocytes, and total white blood cells as well as epinephrine, TNFα, cholesterol, and triglycerides. Cortisol and insulin were not affected. Heat stress reduced (P &lt; 0.05) blood pressure and heart rates in all lambs and increased (P &lt; 0.05) left ventricular wall thickness in unsupplemented but not ractopamine-supplemented lambs. No cardiac arrhythmias were observed. Muscle glucose uptake did not differ among groups, but insulin-stimulated glucose oxidation was reduced (P &lt; 0.05) in muscle from heat-stressed lambs. These findings demonstrate that heat stress impairs growth, metabolism, and well-being even when the impact of feed intake is eliminated by pair-feeding and that systemic inflammation and hypercatecholaminemia likely contribute to these deficits. Moreover, ractopamine improved muscle growth indicators without worsening the effects of heat stress.

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