The focus of this Blog is our dogs’ normal thermoregulatory mechanisms and how these might impact on their Scent Detecting activities during the warmer summer months. If you feel that your dog is struggling in any way with the heat, SEEK IMMEDIATE QUALIFIED VETERINARY ASSISTANCE.
With day-time temperatures in the UK currently reaching anything between 25°C and 30ºC, social media has seemingly gone into overdrive with dire warnings of the dangers this heat may pose to our dogs. Owners are being advised to curtail all usual activities in a bid to keep their dogs cool and many sporting events have been cancelled or postponed. But what about our scent detecting dogs? Can they continue to work in these high temperatures or should we keep them in the shade until the cooler weather returns?
Some background …
Without sweat glands, panting (with accompanying evaporative cooling from the upper respiratory tract) is the main means by which our dogs are able to maintain their normal body temperature of between 37.5°C and 39.1°C (Gazit et al, 2003. Jordan et al, 2016). Any deviations from this narrow range can interfere with normal cellular function (Bear et al, 2016) and, in extreme cases, may result in death.
Our dogs are considered thermally stable when any extra heat they gain is matched by the equivalent amount of heat loss (Stanley, 1980). The thermoneutral zone (TNZ) is the environmental temperature range (between 20°C – 30°C) at which our dogs can maintain their normal body temperature without having to expend energy to either increase heat production or heat loss (Jordan et al, 2016).
The total heat load our dogs experience is made up of both environmental and metabolic factors. If the ambient temperature exceeds our dogs’ body temperature then they will absorb heat from the environment (Jordan et al, 2016). While the heat produced by our dogs’ organs remains fairly constant, heat production by their skeletal muscle is dependent on their activity levels. Up to 80% of our dogs’ body heat is produced by their working muscles (Stanley, 1980).
A little bit of anatomy and physiology … well … quite a lot actually!
Cold– and Warm-sensitive neurons, found in the pre-optic area of the anterior hypothalamus of our dogs’ brains, detect (and respond to) changes in circulating blood temperature. In the case of any rise in temperature, there is a reduction in the release of Thyroid Stimulating Hormone (TSH) from the anterior pituitary gland resulting in a slowing down of our dogs’ metabolism. Blood is shunted toward our dogs’ peripheries to help dissipate heat through the skin and you might start to notice some behavioural changes including a desire to seek shady areas. In addition, our dogs involuntary motor response is to pant (Bear et al, 2016. Hardy et al, 1964).
If you’d like to find out a little more about the hypothalamus and the pre-optic area … just follow these three links.
Goldberg, et al (1981) have identified three patterns of breathing exhibited by dogs’ as their need for evaporative cooling increases either because of increasing environmental temperature or exercise load. As previously mentioned, up to 80% of our dogs’ body heat is produced by working skeletal muscle!
- Pattern I – Inhalation and Exhalation through the nose.
This pattern of breathing is characteristic of the resting dog and, in Goldberg, et als (1981) study was observed in dogs who were either resting in environmental temperatures below 26°C or running at slow speeds in cooler temperatures (10°C).
As inhaled air travels to the lungs, it is warmed and humidified by the moist nasal mucosa. In turn, the nasal mucosa is cooled. On exhalation, air loses its heat to the now, cooler, nasal mucosa and water condenses. This counter-current heat exchange system helps our dogs conserve heat and moisture that might otherwise be lost to the external environment.
In contrast, when our dogs’ need to lose heat, this heat-exchange mechanism can be circumvented by a) vasodilation of the nasal mucosa between inhalation and exhalation and b) switching to exhalation through the mouth as in Patterns II and III.
- Pattern II – Inhalation through the nose. Exhalation through the nose and mouth.
Goldberg, et al (1981) observed this pattern of breathing in dogs either resting quietly in environmental temperatures ranging between 30°C and 42°C or during exercise (except when running slowly at low temperatures as in Pattern I). In these types of environmental and exercise conditions, dogs breathing was seen to oscillate between patterns II and III.
The dogs normal, resting, respiratory rate of between 10-35 breaths / minute (average 24 breaths / minute) increases to approximately 250 breaths / minute. Interestingly, this panting frequency matches the active sniffing frequency of the scent detecting dog (3-7Hz = 3-7 sniffs / second). Panting and active sniffing frequencies are thought to minimise energy expenditure (Craven et al, 2010. Settles et al, 2002).
Although our dogs can now by-pass the heat exchange system in the nose and increase heat loss by exhaling through their mouths, heat loss still occurs mainly in the nose. Vasodilation of the nasal mucosa, with extra moisture being provided by two lateral nasal glands (Steno’s glands) which open through ducts just inside our dogs’ noses, increases evaporative cooling. As breathing rate increases, so does secretion of fluid from these glands (Blatt, et al, 1972).
- Pattern III – Inhalation through the nose and mouth. Exhalation through the nose and mouth.
This pattern of breathing is seen in situations of severe heat stress. The amount of time our dogs use this pattern of breathing increases alongside increases in environmental temperature and exercise load. According to Goldberg, et al (1981), exercise will increase our dogs heat load more so than an increasing environmental temperature.
Lingual blood flow (blood flow to the tongue) increases during moderate heat stress alongside Salivation. Saliva production is governed by the hypothalamus as one of its thermoregulatory responses. Evaporative cooling takes place as dry air is inhaled across the moist tongue and mouth.
Unfortunately, although these three respiratory patterns can be useful signposts to us with regard to how our dogs are coping with the environmental temperature or exercise, Baker, et al (1989) warn that dehydrated dogs will reduce thermoregulatory evaporation in order to reduce water loss. In short, a dehydrated dog will have a lower respiratory rate with a consequent higher body temperature as panting is reduced! Baker, et al (1989) observed a rapid recovery of panting in their study dogs after they were able to drink water.
So … What does all of this mean for our Scent Detecting dogs?
Our dogs’ ability to detect their target odour is largely dependent on their ability to sniff (Mainland et al, 2006). During normal breathing, approximately 12-13% of inspired air will reach the chemosensory area of our dogs noses – the olfactory epithelium – but, importantly, active sniffing will increase this amount by another 2-3% (Craven et al, 2010).
In high temperature environments or, after strenuous physical activity, our dogs’ need to divert attention away from the scent detecting task (and active sniffing) and toward maintaining their body temperature within normal limits (Gazit et al, 2003). As previously discussed, this requires our dogs to pant.
Unfortunately, when our dogs pant, not only are they NOT actively sniffing but “a large turbulent jet is expired from the mouth, obscuring any scent-bearing air currents in the vicinity. The dog must therefore normally stop panting in order to sniff” (Settles et al, 2002). Our dogs cannot sniff and pant at the same time!
In Gazit et als (2003) study investigating explosives detection by sniffer dogs working in hot climates, they found a decrease in “olfactory efficiency [resulting] mainly from overheating [which caused] physiological and behavioural resources to be diverted from concentration on the assigned task and applied instead to methods of body cooling”. Interestingly, however, after training in, and exposure to, high temperature working environments, their scent detecting performance improved. This is likely to have been due to the process of acclimatization whereby the animal becomes physically adjusted to, and able to tolerate, the temperature of their environment (University of Iowa: Hospitals and Clinics, 2016). Amongst other things, acclimatization to heat decreases the temperature threshold at which heat dissipation mechanisms are activated (Bruchim et al, 2014. Horowitz, 1998); Our dogs’ “cooling strategies” come into play much sooner than they would pre-acclimatization.
According to Horowitz (1998), “heat acclimation is switched on in response to persistent, moderate ambient heat and takes time to develop but is long acting (several weeks)”. Partial acclimatization may take from 10 – 20 days while full acclimatization may take up to 60 days (Jordan et al, 2016). Certainly, from a personal perspective, this rings true for me. Now, a number of weeks into these unusually high UK temperatures, my own dogs are far more active than they were in the early days of this ongoing heatwave.
So … Should we retire our Scent Detecting dogs until the temperature drops?
With a little care, thought and planning, Summer Scent Detecting is still perfectly possible, however, each of us must decide for ourselves whether it is safe to proceed.
A few points to keep in mind
- Our dogs pant in response to an increasing body temperature – we need to keep Scent Detecting sessions short and, wherever possible, work in areas with plenty of shade / protection from the sun.
- Panting is an involuntary motor response which helps our dogs’ maintain their body temperature within normal limits – they cannot choose to stop panting and continue sniffing. Scent Detecting activities may take longer than expected as our dogs pant rather than sniff. Ensure plenty of “down-time” and allow our dogs’ to take extra breaks whenever they want to.
- Our dogs will cease to pant (and overheat) if they are dehydrated – Ensure a plentiful supply of fresh drinking water at all times. Do not “force” a dog to drink.
- Remember that up to 80% of our dogs’ body heat is produced by their working skeletal muscles – Scent Detecting may be a far safer activity for our dogs in high temperature environments than other, more strenuous, sports and hobbies. No dog should be forced to exercise.
- Take extra care if you own any of the brachycephalic breeds, eg; pug – the anatomy of their head is likely to interfere with their ability to pant and regulate their temperature (Stanley, 1980).
- Our dogs’ can acclimatize to high ambient temperatures but it takes time – Do not expect our dogs’ to be working as enthusiastically, or at as fast a speed, as they would normally during the cooler months.
Happy Scent Detecting!
As with all of my blogs, I include a reference list. This allows you to investigate the topic a little further, check out the sources of my information and decide for yourself whether my interpretations of the literature accurately reflect the author’s work. Happy reading.
© Scent : Detect : Find Ltd 2018
References / Further Reading
- Baker M A and Turlejska E (1989) Thermal panting in dehydrated dogs: effects of plasma volume expansion and drinking. European Journal of Physiology. 413. 511-515.
- Bear M F, Connnors B W and Paradiso M A (2016) Neuroscience. Exploring the Brain. 4th Ed. Philadephia: Wolters Kluwer.
- Blatt C M, Taylor C R and Habal M B (1972) Thermal Panting in Dogs: The Lateral Nasal Gland, a Source of Water for Evaporative Cooling. Science. 804-805.
- Bruchim Y, Aroch I, Eliav A, Abbas A, Frank I, Kelmar E, Codner C, Segev G, Epstein y and Horowitz M (2014) Two years of combined high-intensity physical training and heat acclimatization affect lymphocyte and serum HSP70 in purebred military working dogs. Journal of Applied Physiology. 117. 112-118.
- Craven B A, Paterson E G and Settles G S (2010) The fluid dynamics of canine olfaction: Unique nasal airflow patterns as an explanation of macrosmia. Journal of the Royal Society. Interface. 7. 933-943.
- Gazit I and Terkel J (2002) Explosives detection by sniffer dogs following strenuous physical activity. Applied Animal Behaviour Science. 81. 149-161.
- Goldberg M B, Langman V A and Taylor C R (1981) Panting In Dogs: Paths Of Airflow In Response To Heat and Exercise. Respiration Physiology. 43. 327-338.
- Hardy J D, Hellon R F and Sutherland K (1964) Temperature-Sensitive Neurones in the Dog’s Hypothalamus. Journal of Physiology. 175. 242-253.
- Horowitz M (1998) Do Cellular Heat Acclimation Responses Modulate Central Thermoregulatory Activity? News Physiological Science. 13. 218-225.
- Jordan M, Bauer A E and Croney C (2016) Temperature Requirements for Dogs. Are they tailored to promote dog welfare? Purdue Extension. October. 1-3.
- Mainland J and Sobel N (2006) The Sniff is part of the Olfactory Percept. Chem. Senses. 31. 181-196.
- Settles G S, Kester D A and Dodson-Dreibelbis L J (2002) The External Aerodynamics of Canine Olfaction. IN: Barth F G, Humphrey J A C and Secomb T W (Eds) Sensors and Sensing in Biology and Engineering. New York: Springer.
- Stanley S M (1980) A Study of Heat Stroke and Heat Exhaustion in the Dog. Iowa State University Veterinarian. 42. 24-27.
- University of Iowa: Hospitals and Clinics (2016) Acclimatization: Adjusting to the Temperature. https://uihc.org/health-topics/acclimatization-adjusting-temperature. Accessed 1.8.2018