Temperature and humidity of expired air of sheep

Evaluation of the Thermal Response of the Horns in Dairy Cattle

Dairy cattle are typically disbudded or dehorned. Little is known, however, about the biological function and role of horns during thermoregulatory processes in cattle, and thus about the potential physiological consequences of horn removal. Anecdotal evidence suggests that dairy cow horns increase in temperature during rumination, and few studies on other bovid species indicate that horns aid thermoregulation. The objective of this study was, therefore, to elucidate a possible thermoregulatory function of the horns in dairy cattle. Using non-invasive infrared thermography, we measured the superficial temperature of the horns, eyes, and ears of 18 focal cows on three different farms in a temperate climate zone under various environmental circumstances. Observations of social and non-social behaviours were conducted as well. Based on environmental temperature, humidity, and wind speed, the heat load index (HLI) was calculated as a measure of the heat load experienced by a cow. The temperature of the horns increased by 0.18 °C per unit HLI, indicating that horns serve the dissipation of heat. Dehorned cows had higher eye temperatures than horned cows, though this result should be interpreted with caution as the low sample size and experimental setup prevent casual conclusions. We did not, however, find changes in horn temperature during rumination, nor with any other behaviours. Our study thus supports a role of horns in thermoregulation, but not related to rumination. These results should be considered when assessing the potential consequences of horn removal, a painful procedure.

The Use of Infrared Thermal Imaging to Determine Functional Nasal Adequacy: A Pilot Study

Objective

The goal of this study was to establish a numeric threshold to separate functional from substantially obstructed noses using comparisons of thermal imaging and subjective scores.

Study Design

An inexpensive smartphone application and hardware attachment that uses infrared thermal imaging was tested to differentiate between substantial nasal blockage from an adequately functioning nose.

Setting

Sequential adult participants who presented to a public hospital otolaryngology clinic between June and August 2018 were asked to complete the Nasal Obstruction Symptom Evaluation (NOSE) tool.

Methods

A thermal video imaging device was used to record the difference in temperature (ΔT) between inspired (I) and expired (E) air at each nostril. The nostril ΔT between I and E air of patients with severe obstruction by the subjective measure (NOSE score) was compared with that of patients with minimal symptoms.

Results

A total of 26 participants were enrolled in the study. During normal respiration, Total ΔT for the nonobstructed group had a mean of 9.0, whereas the Total ΔT for the obstructed group had a mean of 7.69, a 17% difference that was statistically significant at P = .045. For the worst-performing nostril tested, ΔT for the nonobstructed group had a mean/median of 4°C, while the obstructed group had a mean of 3.23°C (median 3; 23.8% difference, P = .023).

Conclusion

Measures of thermal imaging, particularly at the threshold between the median scores of the worst-performing nostril, may be a useful clinical test to differentiate between a substantially obstructed nose from an adequately functioning nose, although more data are required.

Two lines of evidence for physiological control of insensible evaporative water loss by a tiny marsupial

We present two independent lines of evidence that a tiny dasyurid marsupial, the ningaui (Ningaui spp.), has acute physiological control of its insensible evaporative water loss below and within thermoneutrality. Perturbation of the driving force for evaporation by varying relative humidity, and therefore the water vapour pressure deficit between the animal and the ambient air, does not have the expected physical effect on evaporative water loss. Exposure to a helox atmosphere also does not have the expected physical effect of increasing evaporative water loss for live ningauis (despite it having the expected effect of increasing heat loss for live ningauis), but increases evaporative water loss for dead ningauis. We discuss the relative advantages and disadvantages of both experimental approaches for demonstrating physiological control of insensible evaporative water loss. An appreciation of physiological control is important because insensible evaporative water loss contributes to both water and heat balance, is clearly under environmental selection pressure, and potentially impacts the distribution of endotherms and their response to environmental change.

Does control of insensible evaporative water loss by two species of mesic parrot have a thermoregulatory role?

Insensible evaporative water loss (EWL) at or below thermoneutrality is generally assumed to be a passive physical process. However, some arid zone mammals and a single arid zone bird can control their insensible water loss, so we tested the hypothesis that the same is the case for two parrot species from a mesic habitat. We investigated red-rumped parrots (Psephotus haematonotus) and eastern rosellas (Platycercus eximius), measuring their EWL, and other physiological variables, at a range of relative humidities at ambient temperatures of 20 and 30°C (below and at thermoneutrality). We found that, despite a decrease in EWL with increasing relative humidity, rates of EWL were not fully accounted for by the water vapour deficit between the animal and its environment, indicating that the insensible EWL of both parrots was controlled. It is unlikely that this deviation from physical expectations was regulation with a primary role for water conservation because our mesic-habitat parrots had equivalent regulatory ability as the arid habitat budgerigar (Melopsittacus undulatus). This, together with our observations of body temperature and metabolic rate, instead support the hypothesis that acute physiological control of insensible water loss serves a thermoregulatory purpose for endotherms. Modification of both cutaneous and respiratory avenues of evaporation may be involved, possibly via modification of expired air temperature and humidity, and surface resistance.

Physiological responses of a rodent to heliox reveal constancy of evaporative water loss under perturbing environmental conditions

Total evaporative water loss of endotherms is assumed to be determined essentially by biophysics, at least at temperatures below thermoneutrality, with evaporative water loss determined by the water vapor deficit between the animal and the ambient air. We present here evidence, based on the first measurements of evaporative water loss for a small mammal in heliox, that mammals may have a previously unappreciated ability to maintain acute constancy of total evaporative water loss under perturbing environmental conditions. Thermoregulatory responses of ash-grey mice ( Pseudomys albocinereus) to heliox were as expected, with changes in metabolic rate, conductance, and respiratory ventilation consistent with maintaining constancy of body temperature under conditions of enhanced heat loss. However, evaporative water loss did not increase in heliox. This is despite our confirmation of the physical effect that heliox augments evaporation from nonliving surfaces, which should increase cutaneous water loss, and increases minute volume of live ash-grey mice in heliox to accommodate their elevated metabolic rate, which should increase respiratory water loss. Therefore, mice had not only a thermoregulatory but also a hygroregulatory response to heliox. We interpret these results as evidence that ash-grey mice can acutely control their evaporative water loss under perturbing environmental conditions and suggest that hygroregulation at and below thermoneutrality is an important aspect of the physiology of at least some small mammals.

Reduction of the Pa(CO2) set point during hyperthermic exercise in the sheep

In animals that rely on the respiratory system for both gas exchange and heat loss, exercise can generate conflict between chemoregulation and thermoregulation. We hypothesized that in panting animals, hypocapnia during hyperthermic exercise reflects a reduction in the arterial CO2 tension (Pa(CO2)) set point. To test this hypothesis, five sheep were subjected to tracheal insufflations of CO2 or air (control) at 3-4 L min(-1) in 3 min bouts at 5 min intervals over 31 min of exercise. During exercise, rectal temperature and minute ventilation (V(E)) rose continuously while Pa(CO2) fell from 35.4+/-3.1 to 18.6+/-2.9 Torr and 34.3+/-2.4 to 18.7+/-1.5 Torr in air and CO2 trials, respectively. Air insufflations did not affect V(E) or Pa(CO2). V(E) increased during CO2 insufflations via a shift to higher tidal volume and lower frequency. CO2 insufflations also increased Pa(CO2), although not above the pre-exercise level. Within 5 min after each CO2 insufflation, Pa(CO2) had decreased to match that following the equivalent air insufflation. These results are consistent with a reduced Pa(CO2) set point or an increased gain of the Pa(CO2) regulatory system during hyperthermic exercise. Either change in the control of Pa(CO2) could facilitate respiratory evaporative heat loss by mitigating homeostatic conflict.

Effect of locomotor respiratory coupling on respiratory evaporative heat loss in the sheep

During galloping, many animals display 1:1 coupling of breaths and strides. Locomotor respiratory coupling (LRC) may limit respiratory evaporative heat loss (REHL) by constraining respiratory frequency (f). Five sheep were exercised twice each, according to a five-step protocol: 5 min at the walk, 5 min at the trot (trot1), 10 min at the gallop, 5 min at the trot (trot2), and 5 min at the walk. Rectal temperature (T(re)), stride frequency, f, REHL, and arterial CO(2) tension and pH were measured at each step. Tidal volume (VT) was calculated. LRC was observed only during galloping. The coupling ratio remained at 1:1 while VT increased continuously during galloping, causing REHL to increase from 2.9 +/- 0.2 (SE) W/kg at the end of trot1 to a peak of 5.3 +/- 0.3 W/kg. T(re) rose from 39.0 +/- 0.1 degrees C preexercise to 40.2 +/- 0.2 degrees C at the end of galloping. At the gallop-trot2 transition, VT fell and f rose, despite a continued rise in T(re). Arterial CO(2) tension fell from 36.5 +/- 1.1 Torr preexercise to 31.8 +/- 1.4 Torr by the end of trot1 and then further to 21.5 +/- 1.2 Torr by the end of galloping, resulting in alkalosis. In conclusion, LRC did not prevent increases in REHL in sheep because VT increased. The increased VT caused hypocapnia and presumably elevated the cost of breathing.