Respiratory heat loss of Holstein cows in a tropical environment

In order to develop statistical models to predict respiratory heat loss in dairy cattle using simple physiological and environmental measurements, 15 Holstein cows were observed under field conditions in a tropical environment, in which the air temperature reached up to 40°C. The measurements of latent and sensible heat loss from the respiratory tract of the animals were made by using a respiratory mask. The results showed that under air temperatures between 10 and 35°C sensible heat loss by convection decreased from 8.24 to 1.09 W m^–2, while the latent heat loss by evaporation increased from 1.03 to 56.51 W m^–2. The evaporation increased together with the air temperature in almost a linear fashion until 20°C, but it became increasingly high as the air temperature rose above 25°C. Convection was a mechanism of minor importance for respiratory heat transfer. In contrast, respiratory evaporation was an effective means of thermoregulation for Holsteins in a hot environment. Mathematical models were developed to predict both the sensible and latent heat loss from the respiratory tract in Holstein cows under field conditions, based on measurements of the ambient temperature, and other models were developed to predict respiration rate, tidal volume, mass flow rate and expired air temperature as functions of the ambient temperature and other variables.This paper forms part of A. S. Campos Maias doctoral thesis.     

Respiratory water loss: A predictive model

A steady-state model, based on a combination of empirical and mechanistic relationships, is developed to predict respiratory water loss from terrestrial vertebrates. Model parameters are evaluated from published data for the banner-tail kangaroo rat (Dipodomys spectabilis). A three-dimensional representation of model behavior is presented, emphasizing the interaction of organismal and environmental variables. The model makes possible the calculation of respiratory water and heat losses for animals in both artificial and natural environments.     

Role of the udder in heat loss from the sheep

Measurements have been made of temperatures on the surface of the udder, the back under the fleece, the exremities, and of the body core in sheep. The temperature on the surface of the udder changes very little in response to changes in ambient temperature, and, unlike the temperature on the back, and of the body core, there was no evidence of a 24 h variation. It is concluded that the udder does not function as an organ of controlled heat loss in sheep.     

Air movement and heat loss from sheep. I. Boundary layer insulation of a model sheep, with and without fleece

A model sheep, made from metal cylinders and hemispheres, was heated electrically. Heat loss by forced convection in a wind tunnel was analysed in terms of the dependence of the Nusselt number (Nu) on Reynolds number (Re). For a bare trunk Nu = 0.095 Re0.684, but with fleece covering the trunk to a depth of 3.5 cm, Nu = 0.0112 Re0.875 when the mean radiative temperature of the the coat was taken as the surface temperature. Heat transfer by convection from the whole body, including legs, was described by Nu = 0.029 Re0.80. However, a bulk Nesselt number should not be used to estimate heat loss from a live sheep in a hot environment if the windspeed is below about 4 m s-1 because the relation between mean surface temperature, Nusselt number and convective heat flux is not unique.     

Respiratory heat loss and core temperatures during submaximal exercise

1. 1. This study examined the effect of inhaling air supersaturated with water on changes of core temperatures in submaximally exercising males.

2. 2. During exercise with inhalation of supersaturated relative to low-air-humidity air, a significant elevation in tympanic temperature (P = 0.009) and a significant decrease in esophageal temperature (P = 0.004) were observed.

3. 3. Forehead skin temperatures significantly decreased during humidified air inhalation (P = 0.02) supporting that this treatment induced greater thermolytic responses that cooled the skin.

4. 4. The results are consistent with the conclusion that heat loss from the upper airways directly influenced human cerebral temperatures as indexed by tympanic temperatures.

     

The effects of thermoregulatory behaviour on the heat loss from shorn sheep as measured by a model ewe for micro-climate integration

A thermostatic, taxidermic model sheep was used to assess the effects of thermoregulatory behaviour of shorn sheep at night in a winter environment with mean air temperatures slightly above freezing, variable wind speeds, rain and cloud cover.Testing in a wind tunnel showed that angle of incidence to the wind had no effect on heat loss at wind speeds < 2 m s⁻¹ (7 km h⁻¹), but at wind speeds of 7 m s⁻¹ (25 km h⁻¹), heat loss was 14% greater when the model was side-on rather than tail- or head-on to the wind.In tests on pasture, standing side-on to the early morning sun reduced heat loss from the model by 33%. Three hours “lying” on the lee side of a 1-m high synthetic Sarlon windbreak on a frosty night resulted in a reduction in heat loss of 6% below that when standing or 11% below that in a standing position in the open. When the model was placed in the centre of a tight group of 16 shorn sheep, its heat loss was reduced by an average of 14%.Heat loss was also reduced if the model was moved from the open, to regions of lower wind speed adjacent to windbreaks; the effect was greater on the leeward than the windward side.The reduction one metre leeward of a grass hedge (hybrid Phalaris) was 15% compared with 12% one metre leeward of a synthetic (Sarlon) windbreak, which is consistent with the preference of shorn sheep to shelter by Phalaris rather than Sarlon windbreaks.The microclimates where heat loss from the model were lowest correspond to those sought by shorn sheep in cold weather, and the results indicate that shorn sheep have very sensitive thermosensing mechanisms and efficient thermoregulatory behaviour.     

Air movement and heat loss from sheep. III. Components of insulation in a controlled environment

The rate of sensible heat loss from a Clun Forest ewe was studied at several fleece depths in a temperature-controlled chamber. A simple resistance analogue was used to describe the heat flow from different body regions. Heat loss from the trunk depends largely on the mean fleece depth l. The fleece resistance was about 1.5 s cm-1 per centimetre depth. Heat transfer through the fleece was accounted for by molecular conduction, thermal radiation and free convection. The fleece conductivity -kb attributed to free convection depends on the mean temperature difference (-Tst---Tct) across the fleece according to the relation -kb = 8.0 (-Tst---Tct)0.53. Estimates of the sensible heat flux from the trunk at environmental temperatures, Ta, between 0 and 30 degrees C range from about 8 W (l = 7.0 cm, Ta = 30 degrees C) to about 160 W (l = 0.1 cm, Ta = 0 degrees C). In contrast, the sensible heat loss from the legs depends mainly on the local tissue resistance. For environmental temperatures between 0 and 30 degrees C, the calculated tissue resistance for this region of the body varied from about 8 to 1 s cm-1. The corresponding heat loss from the legs was between 10 and 20 W, compared with between 3 and 7 W from the head. The fastest heat loss from the legs occurred at an environmental temperature of about 12 degrees C. Although the proportion of the heat loss from the extremities depends on environmental temperature, the total heat loss (sensible or latent) was closely related to the mean skin temperature of the trunk.     

Respiratory water loss in insects

The contribution of respiratory transpiration to overall water loss in insects is contentious. Misgivings concerning the importance of this route of water loss have arisen largely as a consequence of work on discontinuous gas exchange cycles (DGC). Most studies have found that respiratory water loss constitutes only a small proportion of total water loss. Thus, it has been argued that modulation of metabolic rate and/or the components of the DGC is unlikely to constitute a fitness benefit. In contrast to these intraspecific studies, interspecific comparative data suggest that, at least in xeric species, respiratory transpiration is an important component of water loss. However, these arguments are confounded by several factors. In DGC-based studies, these include multiple effects of the experimental treatments, the absence of a null expectation for the contribution of respiratory to total water loss, and problems with the use of proportions as a way of assessing the importance of respiratory water loss. The interspecific studies are confounded by the likely significance of influences other than water conservation on metabolic rate, the absence of analyses of phylogenetic independent contrasts, and little information on behavioral differences between species. Future work should be based on a strong inference approach and designed in such a way that these problems can be resolved. Moreover, in the case of the DGC it should be recognized that several factors are likely to influence this gas exchange pattern, and that they probably act in concert, especially during dormancy.     

Respiratory flow in a realistic tracheostenosis model

The possible mechanism of wheeze generation in tracheostenosis was identified by measuring inspiratory and expiratory flow in a "morphological and distensible" realistic tracheostenosis model. The shape of the model was based on CT (Computed Tomography) images of a patient that had tracheostenosis. A trachea consists of tracheal cartilage rings and smooth muscle. Spatial variation of wall distensibility was achieved in the model by varying the wall thickness based on the elastic modulus measured in pig airways. The spatial variation influenced the flow in the airway and the turbulence production rate decreased faster at smooth muscles. Using the model, we investigated the mechanism of wheeze generation by focusing on the turbulence intensity. The turbulence intensity in expiratory flow was about twice that in inspiratory flow, and larger vortices existed in post-stenosis in expiratory flow, and thus might contribute to wheeze generation.     

Air movement and heat loss from sheep. II. Thermal insulation of fleece in wind

Penetration of an animal's coat by wind reduces its thermal insulation and increases heat loss to the environment. From studies of the sensible heat loss from a life-sized model sheep covered with fleece, the average fleece resistance -rf(s cm-1) was related to windspeed u (m s-1) by 1/-rf(u) = 1/-rf(0)+cu, where c is a dimensionless constant. As c is expected to be inversely proportional to coat depth l, the more general relation -k(u) = -k(0)+c'u was evaluated, where -k = l/-rf is the thermal diffusivity (cm2 s-1) of the fleece and c' = cl is another constant (cm). The orientation of the model to the wind had little effect on the bulk resistance of the fleece, but the resistance on the windward side was substantially lower than on the leeward side.     

Age and heat tolerance in sheep

The influence of age on heat tolerance in sheep was investigated in two hotroom studies. The rectal temperature and respiratory rate response of 16-month old Dorset Horn x Merino and of 18-month old Merino ewes did not differ significantly from that of their respective mature (4.5 to 6 year old) counterparts.

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Zusammenfassung Der Einfluss des Alters auf die Wärmetoleranz von Schafen wurde in zwei Heissluftkammern untersucht. Die Rektaltemperatur und die Wirkung auf das Atemvolumen bei 16 Monate alten Dorset Horn x Merino — und bei 18 Monate alten Merino — Mutterschafen unterschieden sich nicht signifikant von denen der älteren(4,5 bis 6-jährigen) Vergleichstiere.

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Resume On a examiné dans deux chambres chaudes l'influence de l'âge sur la tolérance des moutons à la chaleur. La température rectale et les répercussions du chaud sur le volume respiré n'a pas présenté de différences significatives entre des brebis Dorset Horn x Mérinos de 16 mois et Mérinos de 18 mois d'une part, et les bêtes de contrôle plus âgées (4,5 à 6 ans) d'autre part.

     

A model of heat flow in the sheep exposed to high levels of solar radiation.

The fleece is an important component in thermoregulation of sheep exposed to high levels of solar radiation. A model written in CSMP has been developed which represents the flow of energy between the sheep and its environment. This model is based on a set of differential equations which describe the flux of heat between the components of the system--fleece, tip, skin, body and environment. It requires as input parameters location, date, time of day, temperature, relative humidity, cloud cover, wind movement, animal weight and linear measurements and fleece length. At each integration interval incoming solar radiation and its components, the heat arising from the animal's metabolism and the heat exchange by long-wave radiation, convection, conduction and evaporative cooling are computed. Temperatures at the fleece tip, skin and body core are monitored.     

Simulation of multidimensional community patterns: towards a comprehensive model

Ecological gradients in the field layer of southern boreal forests in South Finland were studied in relation to the dominant tree species and the age of forest stands. The data are from a systematic sample of 529 plots from an area of 150 × 200 km, collected in the Third National Forest Inventory in 1951–53. Detrended correspondence analysis (DCA) was applied to log-transformed species cover values. It revealed three main gradients: fertility, moisture, and the effect of cattle grazing in forests (still extensive in the early 1950's). The fertility gradient dominated the first axis and the two latter sources of variation confounded with it in a complex manner in the first two axes of DCA. The second DCA axis was associated with canopy effects on understory pattern, with Pinus and Picea having opposite and Betula intermediate effects. These results were compared with an ordination model of Cajander's forest site types, based on DCA of independent, ideal data of 107 indicator species. The fertility gradient recovered by the model was almost identical to that obtained from the field data. The gradient was also stable from intermediate-age (40–69 yrold) to older forests. The forest site types showed rather large overlaps with main neighbouring types in composition of ground vegetation or nutrient status of the humus. Competitively efficient feather-mosses, which are dependent on nutrients released from the tree crowns, are considered important regulators of the understory vegetation. Accordingly, alternative approaches to the forest site type classification to be used in boreal forests treated by modern intensive forestry should give more weight to the effect of the canopy trees.     

Copper-associated liver disease: a proteomics study of copper challenge in a sheep model

Sheep display a variant phenotype with respect to their susceptibility to copper and derivative pathology. The North Ronaldsay sheep are acutely sensitive to environmental copper while the Cambridge breed is much more copper-tolerant. A study of protein expression in the liver of the two different breeds of sheep as a result of copper challenge would aid in the understanding of their differing pathophysiologies and contribute to knowledge of copper toxicosis in man. In this initial study, Cambridge breed sheep were challenged with oral copper and liver proteins were analyzed by two-dimensional (2-D) gel electrophoresis. Proteins whose expression pattern was modified by copper exposure were then identified by peptide mass fingerprinting using matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. In conclusion, the pattern of changes in protein expression were consistent with an early adaptive response to oxidative challenge. This was followed by evidence of an impaired ability of the liver to compensate as copper loading increased, accompanied by oxidative stress-induced injury.     

Toward a comprehensive model for induced endoreduplication

Both the biological significance and the molecular mechanism of endoreduplication (END) have been debated for a long time by cytogeneticists and researchers into cell cycle enzymology and dynamics alike. Mainly due to the fact that a wide variety of agents have been reported as able to induce endoreduplication and the diversity of cell types where it has been described, until now no clear or unique mechanism of induction of this phenomenon, rare in animals but otherwise quite common in plants, has been proposed. DNA topoisomerase II (topo II), plays a major role in mitotic chromosome segregation after DNA replication. The classical topo II poisons act by stabilizing the enzyme in the so-called cleavable complex and result in DNA damage as well as END, while the true catalytic inhibitors, which are not cleavable-complex-stabilizers, do induce END without concomitant DNA and chromosome damage. Taking into account these observations on the induction of END by drugs that interfere with topo II, together with our recently obtained evidence that the nature of DNA plays an important role for chromosome segregation [Cortes, F., Pastor, N., Mateos, S., Dominguez, I., 2003. The nature of DNA plays a role in chromosome segregation: endoreduplication in halogen-substituted chromosomes. DNA Repair 2, 719-726.], a straightforward model is proposed in which the different mechanisms leading to induced END are considered.     

Long-term follow-up post-cryosurgery in a sheep breast model.

This study constitutes the advanced stage of an ongoing project for the development of cryosurgical devices and techniques for breast cryosurgery. The current study focuses on the long-term follow-up post-cryosurgery in a sheep breast model. Results of this study indicate that the cryotreatment site in a sheep breast model cannot be identified up to 5 months post-cryosurgery by means of ultrasound, mammography, or MRI. Histology findings of this study further indicate that there is no gross or microscopic difference between lesions that have been subject to one versus three freeze/thaw cycles. Under either cryosurgical protocol, there is a main cryoinjured region that has uniform destruction of epithelium and healing scar formation and a transition zone of damaged lobules without acini, surrounded by healthy tissues. The cryoinjured region at 5 months post-cryosurgery was found to be about half the diameter of the ultrasound-imaged frozen region during the cryoprocedure. This study shows that, in terms of recovery and regeneration, surgical excision appears to have an advantage over cryosurgery, which results in a more rapid healing process. Based on observations that the cryoinjured region is no smaller than the ultrasound-imaged ice-ball and that the typical thickness of the transition zone is up to 5 mm, a conservative use of the cryosurgical device developed for the current study in an ultrasound-monitored cryoprocedure requires at least 5 mm safety margins of the frozen region radius around the target region.