Cutaneous water loss and respiration rates of various breeds of sheep at high ambient temperatures

Summary The sweating and respiratory rates in rams of Rambouillet (R), Chokla (C), Malpura (M), R × C and R × M breed/breed crosses were recorded when housed in sheds or exposed to 20, 25, 30, 35 and 42°C ambient temperatures in a climatic chamber. The sweating (cutaneous moisture) was higher (P<0.05) in Rambouillet and its crosses than the natives, the Malpura sheep producing the least sweat at all temperatures. There was no breed difference in the response of increase in sweating up to 35°C but at 42°C the Chokla showed a considerable increase. Sweating was more pronounced on the shoulder than on the mid-side region. Sweating and respiratory rates increased (P<0.05) with the increase in ambient temperature. The Rambouillet exhibited the highest increase in respiration rate at 25°C and the trend continued up to 42°C. The relationship between fleece characteristics, evaporative heat loss and heat tolerance of sheep is discussed.

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Perdida Cutanea De Agua Y Frecuencia Respiratoria De Varias Razas De Ovejas Sometidas A Temperaturas Ambientales Altas

Resumen Se registraron las frecuencias sudorípara y respiratoria en carneros de las razas Rambouillet (R), Chokla (C), Malpura (M), R × C y R × M, alojados en cobertizos o expuestos a temperaturas ambientales de 20, 25, 30, 35 y 42°C en una cámara climática. El sudor (humedad cutánea) fue mayor (P<0.05) en carneros Rambouillet y sus cruces que en animales nativos, siendo la raza Malpura la que menos sudor produjo bajo todas las temperaturas. No se presentaron diferencias significativas entre las diferentes razas respecto a la humedad cutánea hasta los 35°C, pero a los 42°C la raza Chokla presentó un aumento considerable. El sudor fue más notorio en la espalda que en la región média. Las frecuencias respiratoria y sudorípara aumentaron (P<0.05) directa y paralelamente a la temperatura ambiental. La raza Rambouillet tuvo la frecuencia respiratoria más alta a los 25°C, incrementandose esta paulatinamente hasta los 42°C. Se discute la relación entre las caracteristicas del vellon, la pérdida de calor por evaporación y tolerancia al calor de las ovejas.

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Niveau Des Pertes D'eau Par Transpiration, Et Rhythme Respiratoire De Differentes Races De Moutons Soumis A Des Temperatures Ambiantes Elevees

Résumé Les pertes par transpiration et le rythme respiratoire de béliers de Rambouillet (R), Chokla (C), Malpura (M) et de croisements R × C et R × M ont été relevés lorsque les animaux étaient en bergerie ou exposés à des températures ambiantes, dans une chambre climatique, à 20, 25, 30 et 42°C. Les pertes d'eau par transpiration ont été plus importantes (P<0.05) chez les mérinos de Rambouillet et les métis par rapport aux animaux de race locale, les Malpura manifestant les déperditions d'eau moindre à toutes les températures.Il n'y a pas eu de différences raciales dans la réponse à l'accroissement de la transpiration jusqu'à 35°C mais à 42°C les Chokla ont manifesté une augmentation considérable.La déperdition d'eau par transpiration cutanée a été plus prononcée au niveau des épaules que sur le côté du milieu du corps. La transpiration et le rythme respiratoire ont augmenté (P<0.05) avec l'accroissement de la température ambiante. Les mérinos de Rambouillet ont montré la plus importante augmentation du rythme respiratoire à 25°C, température qui a continué de s'accroître jusqu'à 42°C, limite supérieure de l'expérimentation.Les relations entre l'influence de la température sur les pertes d'eau par évaporation et al tolérance des moutons à la chaleur sont discutées.

     

Pressures in the right side of the heart and esophagus (pleura) in ponies during exercise before and after furosemide administration

Pressures in the right side of the heart and esophagus (pleural) have not been determined in the exercising equine subjects. In the present study, 8 healthy ponies were examined to determine the changes in these variables caused by 2 degrees of exercise done on a treadmill (heart rate:183 +/- 5 beats/min [trot] and 220 +/- 6 beats/min [canter]). Measurements were also made during both degrees of exertion 10 minutes and 120 minutes after furosemide (1.0 mg/kg) administration. It was observed that both gaits resulted in significant increases in pulmonary artery, right ventricular, and right atrial pressures. The pulmonary artery systolic, mean, and diastolic pressures during strenuous exertion were 306%, 252%, and 242% of the respective resting values. At canter, when respiratory frequency (138 +/- 4 breaths/min) is synchronized with stride frequency, the delta esophageal pressure approached 30.4 +/- 2.86 cm of water. During exercise 10 minutes after furosemide administration, the increment in right atrial pressure was markedly attenuated. During strenuous exertion 120 minutes after furosemide administration, the right atrial and pulmonary arterial pressures increased, but to a significantly lower level than did the prefurosemide values. However, the mean pulmonary artery pressure was still 240% of the resting value. It is concluded that marked pulmonary hypertension is a consistent feature of moderate, as well as strenuous, exertion in the pony. Although furosemide administration attenuated the pulmonary hypertension somewhat, the significance remains unclear.     

Distribution of blood flow during moderate and strenuous exercise in ponies (Equus caballus)

Blood flow to the brain, heart, kidneys, diaphragm, and skeletal muscles was studied at rest and during graded treadmill exercise, using radionuclide-labeled microspheres (15 microns diameter), in 11 healthy adult ponies. Hemodynamic changes brought about by exercise included marked increases in cardiac output, mean aortic pressure, left ventricular end-diastolic pressure, and right ventricular systolic and end-diastolic pressures. Blood flow to the brain stem and cerebral hemispheres was unchanged during both moderate exercise (heart rate = 154 +/- 3 beats/min) and severe exercise (heart rate = 225 +/- 7 beats/min). Despite marked hypocapnia during severe exercise, cerebellar blood flow increased by 32% above control value (94 +/- 7 ml/min/100 g). Myocardial blood flow increased transmurally with both levels of exercise. The endo:epi (inner:outer) perfusion ratio for the left ventricle and the interventricular septum decreased during exercise. It was, however, not different from unity. During severe exercise, renal blood flow decreased to 19% of its control value. Blood flow to the diaphragm exceeded that to the skeletal muscles during both intensities of exercise. Blood flow to the exercising muscles of the brachium and thigh increased by 31- to 38-fold during moderate exercise and by 70- to 76-fold during severe exercise. It is concluded that the cardiovascular response to strenuous exercise in the pony included an increase in blood flow to the cerebellum, myocardium, diaphragm, and exercising skeletal muscles, while blood flow was diverted away from the kidneys. It would appear that the pony's cardiovascular response to severe exercise is similar to that of persons.     

Differential accumulation of osmolytes in 4 cultivars of peanut (Arachis hypogaea L.) under drought stress

The study investigates the differential accumulation of osmolytes and their contribution to osmotic adjustment in leaf tissue of peanut under drought stress. Plants of four peanut cultivars, obtained from ICRISAT, with varying degrees of drought tolerance were subjected to 10, 15, and 20 days of drought stress by withholding irrigation to 20-day-old seedlings. Leaf samples were collected on 31^st, 36^th, and 41^st days from these stressed plants along with their respective controls. The results indicated that ICGV 91114 was the most drought-tolerant variety followed by ICGS 76 and J 11, while JL 24 was the most drought susceptible. The leaves of ICGV 91114 maintained higher RWC and chlorophyll pigments under water stress compared to JL 24. The contents of all the biochemicals were found to be the maximum in ICGV 91114 and least in JL 24 during stress periods. Drought induced increase in the contents of TSS and TRS were significantly higher in ICGV 91114 under 15 days of water stress compared to the other three varieties and stress periods, while TLP, total free amino acids and total proline were higher in 20-day-old stressed plants of ICGV 91114 and the lowest in 10-day-old stressed plants of JL 24. In the control plants of all four varieties, there was a steady increase in the contents of all these biochemicals with an increase in the age of the plants. The results suggest that osmolytes act as important compatible solutes to maintain osmotic balance, to protect cellular macromolecules, and scavenge free radicals under water stress conditions.     

Intravenous pentoxifylline does not affect the exercise-induced pulmonary arterial, capillary or venous hypertension in Thoroughbred horses

The present study was carried out to examine whether intravenously administered pentoxifylline-a phosphodiesterase inhibitor which increases red blood cell deformability and decreases blood viscosity-would attenuate the magnitude of exercise-induced pulmonary capillary hypertension in healthy, fit Thoroughbred horses and in turn, diminish the occurrence of exercise-induced pulmonary hemorrhage (EIPH). Experiments were carried out on six healthy, sound, exercise-trained Thoroughbred horses. Hemodynamic data were collected at rest, and during exercise performed at 8 and 14 m/sec on 3.5% uphill grade in the control (no medications) and the pentoxifylline (8.5 mg/kg, i.v.) experiments. The sequence of treatments was randomized for every horse and 7 days were allowed between treatments. Galloping at 14 m/sec on 3.5% uphill grade elicited maximal heart rate. In both treatments, simultaneous measurements of phasic and mean right atrial and pulmonary arterial, capillary and wedge pressures were made using catheter-tip-manometers whose signals were carefully referenced at the point of the left shoulder. In the control study, exercise resulted in progressive significant increments in heart rate, right atrial and pulmonary arterial, capillary and venous pressures; thereby, confirming that exercising Thoroughbreds develop significant pulmonary hypertension. All horses experienced exercise-induced pulmonary hemorrhage (EIPH) in the control experiments. Pentoxifylline administration to standing horses caused anxiety, tachycardia, muscular fasciculations/tremors and mild sweating, but statistically significant changes in right atrial and pulmonary arterial, capillary and venous pressures were not detected. Exercise in the pentoxifylline treatment also resulted in progressive significant increments in heart rate and right atrial as well as pulmonary vascular pressures, but these data were not statistically significantly different from those in the control study and the incidence of EIPH remained unchanged. Thus, it was concluded that i.v. pentoxifylline is ineffective in attenuating the exercise-induced pulmonary arterial, capillary and venous hypertension in healthy, fit Thoroughbred horses.     

Inhibition of Nitric Oxide Synthase with L-NAME Does Not Increase Lactate Production at Rest or During Short-term High-intensity Exercise in Thoroughbred Horses

The present study was carried out to determine whether inhibition of nitric oxide (NO) synthase promotes anaerobic metabolism in exercising horses, resulting in a significantly increased blood lactate concentration. N -nitro-L-arginine methyl ester (L-NAME) is a potent inhibitor of NO synthase that has been tested in horses and other species. Two sets of experiments, namely placebo (saline control) and L-NAME (20 mg/kg, IV) studies, were carried out on seven healthy, sound, exercise-trained, Thoroughbred horses in random order, 6 to 7 days apart. In both experiments, an incremental exercise protocol was used and data were obtained at rest, during submaximal exercise performed at 8 m/s on a 4.5% uphill grade, and during galloping at 14 m/s on a 4.5% uphill grade – a workload that not only elicited maximal heart rate and induced exercise-induced pulmonary haemorrhage, but also could not be sustained for more than 90 s. Measurements were also made in the recovery period. Mixed-venous blood samples, obtained at matched intervals in the two sets of experiments, were analysed in triplicate for determining the lactate concentration. Following administration of L-NAME, significant bradycardia occurred at rest (27±1 vs 37±2 beats/min in the placebo trials; p<0.0001) as well as during submaximal exercise (183±4 vs 200±4 beats/min in the placebo trials; p<0.001), but the heart rate increased during galloping at 14 m/s on a 4.5% uphill grade to reach values observed in the placebo trials (215±2 beats/min) and significant differences were not found. At rest, the mixed-venous blood lactate concentration was similar in the two experiments. With exercise, the mixed-venous blood lactate concentration increased progressively as work intensity increased in both trials, but significant differences were not found between the placebo and the L-NAME experiments during submaximal exercise, near-maximal exercise or recovery. These experiments demonstrated that inhibition of NO synthase in Thoroughbred horses does not promote enhanced anaerobic metabolism at rest or during short-term incremental exercise leading to galloping at maximal heart rate.     

Cerebral, renal, adrenal, intestinal, and pancreatic circulation in conscious ponies and during 1.0, 1.5, and 2.0 minimal alveolar concentrations of halothane-O2 anesthesia

Blood flow to the brain, kidneys, adrenal glands, pancreas, and small intestine was studied in 8 healthy ponies while awake (control) and during 1.0, 1.5, and 2.0 minimal alveolar concentrations (MAC) of anesthesia produced, using halothane vaporized in oxygen. During the anesthesia steps, intermittent positive-pressure ventilation was used to ensure isocapnia. Organ blood flow was determined with 15-micron (diameter) radionuclide-labeled microspheres, after allowing 30 minutes of equilibration at each of the 3 preestablished end-tidal halothane concentrations. The sequence of 1.0, 1.5, and 2.0 MAC levels of anesthesia (0.90, 1.35, and 1.80% end-tidal halothane) was randomized for every animal. In the awake ponies, cerebral blood flow in the cortical (106 +/- 15 ml/min/100 g) and deep gray (103 +/- 12 ml/min/100 g) matter was approximately 5-fold of that in the white matter (22 +/- 3 ml/min/100 g). In the brain stem, there was a decreasing gradient of blood flow from the cranial (thalamohypothalamus: 65 +/- 8 ml/min/100 g) to caudal regions (medulla: 34 +/- 5 ml/min/100 g). Vasodilatation occurred in all regions of the brain with halothane-O2 anesthesia; the decrease in vascular resistance reached its nadir at 1.5 MAC. In the medulla and pons, blood flow increased above control values, with each of the 3 concentrations of halothane, but in the midbrain and thalamohypothalamus, it remained similar to the control value. In the cerebral white matter and cerebellum, blood flow increased with 1.0 and 1.5 MAC of halothane anesthesia, whereas mean aortic pressure decreased to 91% and 74% of the control value. Blood flow in the cerebral cortex was not different from the control value, even at 2.0 MAC of halothane, despite a 49% reduction in perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)