This is a guest article by Michelle Townley BVM&S MRCVS, Veterinary Advisor, MSD Animal Health

 

Have you ever stopped to consider how you came to decide what a normal body temperature is for your patients? Or noticed that what you would consider to be a temperature in the pyrexic range is different to that of your colleagues?

How can you be certain that your interpretation of a body temperature measurement in a dog or cat is accurate for that particular individual?

You may be surprised to know that what most veterinary professionals may consider as a normal reference range for body temperature is based on little robust evidence-based veterinary literature!

In fact, normal body temperature is poorly defined in veterinary literature. The expectation for a reference range is that a suitably large population has been used with a robust statistical analysis performed to determine a “normal” range, with 95% of that population sitting within it. The reality is that reference ranges stated in textbooks often fail to state their primary source, which makes it impossible to know the size or demographics of the population used, or whether the range was statistically calculated (see Table 1).

Table 1. A “normal” reference range for cats doesn’t exist as demonstrated by the variable reference ranges shown in the table below from several different sources.

Normal Reference intervals in cats Publications
37.8 – 39.2°C Khan CM and Line S.  The Merck Veterinary Manual. White House station, NJ: Merck and Co, 2010, p. 2822

Smith VA et al. comparison of auxiliary, tympanic membrane and rectal temperature measurements in cats. J Feline Med surg. 2015

37.8 – 38.9°C Hartman K and Levy JK. Feline Infectious Diseases. London: Manson publishing, 2011, p. 215
37.2 – 39.2°C Shojai AD.  The First Aid Companion for Dogs and Cats.  Emmaus, PA: Rodal, 2001, p. 248
38.0 – 38.5°C Lane DR and Guthrie S.  Dictionary of Veterinary Nursing. Second edition. Edinburgh: Elsevier, 2004, p. 201
38.1 – 39.2°C Frederichs K, Barnhart K, Blanco J, et al.  Guidelines for the determination of reference intervals in veterinary species and other related topics. Wayne, PA: Clinical and Laboratory Standards Institute, 2008.

Based on this, how can we be sure that the reference range quoted is accurate or applicable to the patient in front of us? Does a normal temperature exist?

In addition, body temperature is not constant. Body temperature, in common with most essential physiological functions such as heart and respiration rate, blood pressure, sleep/wake cycle etc., also follows a circadian rhythm. A 2003 study demonstrated this for the first time in seven female beagle dogs, where rectal temperature was measured every 2 hours for 1 week under rigorously controlled conditions (ambient temperature, lighting, exercise and diet). Interestingly the mean rectal temperature in this study was 39.1°C, which is 0.2°C above the body temperature (38.9°C) generally considered “normal” in dogs. The data from all seven dogs supported the same conclusions: body temperature started to increase immediately after feeding and lasted until lights-out, 8 hours later (see Figure 1). Feeding was not the cause of the day-long increase in body temperature. Given that the environmental conditions were strictly controlled the only cause for the change was endogenous.

Figure 1: The graph demonstrates how the circadian rhythm affects body temperature. This is a representative record of the body temperature of a dog over 7 consecutive days. The data points correspond to 2-hour bins. The white and black bars above the graph indicate the duration of the light and dark phases of the light-dark cycle (Refinetti R and Piccione g., 2003).

Individual physiological factors also contribute to variation in an individual’s body temperature and include breed, age, sex, body condition, level of activity and stress levels. Given the level of individual variation surely it would make sense to get an understanding of an individual pet’s temperature range in order to interpret body temperature measurements accurately?

“Gold standard” temperature monitoring

To measure true core temperature either blood temperature, urinary bladder temperature or oesophageal temperature must be measured. However, these methods are invasive and impossible to utilise in the conscious patient.

Rectal thermometry remains the “gold standard” for temperature measurement based on its good correlation with core body temperature and familiarity within the veterinary profession, however this method isn’t without its drawbacks or inaccuracies. It can be stressful and not always well tolerated in conscious animals. Rectal temperature measurements can be affected by faecal material, rectal inflammation, thrombotic conditions, peristalsis, muscle tone, physical activity, and even just by having the thermometer inserted at an insufficient depth. It can also be the cause of cross-contamination of rectal bacterial flora between patients.

An alternative method avoiding the drawbacks mentioned above is available – and it is as simple as reading a microchip, especially if that chip is a HomeAgain® Thermochip®.

HomeAgain® Thermochip® is a microchip with a difference, as it has an integrated temperature biosensor. Obtaining a temperature reading is as easy as scanning the microchip with a compatible scanner, such as the SureSense® Universal microchip reader or the Global Pocket Reader® Plus. As the temperature is measured in the subcutaneous space (where the microchip is implanted) it does not read the same temperature as a rectal thermometer – so these two methods cannot be directly compared. However, given this method is easier, less invasive and can be performed repeatedly it is simple method to ascertain an individual’s temperature reference range.

Reliability and accuracy

The HomeAgain® Thermochip® microchip is just as reliable and accurate as your trusty digital rectal thermometer, as an independent laboratory study demonstrated. This study compared the temperature readings of 10 HomeAgain® Thermochip® microchips with 4 digital thermometers placed in the same temperature-controlled conditions between 33°C and 43°C at 0.5°C intervals and confirmed the reliability and accuracy of HomeAgain® Thermochip® (see Figure 2).

Figure 2: Temperatures collected by HomeAgain Thermochips were as reliable as those taken by 4 digital thermometers between 33°C and 43°C in 0.5°C intervals under the same temperature-controlled conditions

The ability to detect a fever is an important factor when considering a different method of recording temperature, and the HomeAgain® Thermochip® is very capable of picking this up. In an unpublished study HomeAgain® Thermochip® was able to detect the same physiological fever patterns as rectal thermometry. In this study 10 Beagle dogs were given an intravenous injection of lipopolysaccharide and their temperatures were monitored 4 to 8 hours after the injection to record the febrile response. Rectal temperatures were taken every 30 minutes and the HomeAgain Thermochip was scanned every 5 minutes. Following fever induction, 2,721 temperatures were collected from the 10 dogs, with the greater majority measured using HomeAgain Thermochip. The challenge response was unique for all dogs but was characterised by an initial decrease in temperature (vasoconstriction) followed by a gradual increase to peak temperature demonstrated by both rectal and HomeAgain Thermochip temperature monitoring following a similar shaped curve (Figure 3).

Figure 3. Graph demonstrating the febrile response pattern to intravenous lipopolysaccharide as monitored by rectal thermometry and Home Again Thermochip. Both temperature monitoring methods follow a similar shaped curve.

Clinical applications and the future of temperature monitoring

Although our reliance on rectal thermometry will not be disappearing anytime soon having an alternative temperature recording method which is reliable, accurate, easy, non-invasive and doesn’t distress the patient may encourage us to change our established routines. Especially if this method allows us to obtain an individual pet’s reference range from which we can interpret temperature variations correctly.

The HomeAgain® Thermochip® microchip can already be used for various clinical applications, including as a screening tool or as part of the clinical examination, monitoring temperature during anaesthesia, surgery and the post-operative period, or for hospitalised patients, particularly those that need regular temperature monitoring.

But what does the future look like?

Popular pet-tech consumer brand, Sure Petcare, has the ability to collect temperature data from pets implanted with temperature-sensing microchips with their connected feeder and fountain products. There are currently thousands of pets using these connected devices today and these have collected millions of temperature measurements, with numbers continuing to grow!

So, if you want your clients, their pets and yourself to benefit from the additional information that a HomeAgain® Thermochip® can contribute to the health data from this connected ecosystem then recommend a HomeAgain Thermochip today!

HomeAgain Website

HomeAgain Facebook

 

Throughout the year, MerlinVet will be sharing guest articles written by our partners. If you’d be interested in being featured on our website please get in touch today.

This year’s Royal Highland Show is taking place from Thursday 22nd June – Sunday 25th June 2023 at Ingliston.
MerlinVet will be sponsoring two sheep classes:
  • Valais Blacknose – Thursday 22nd June (afternoon)
  • Hampshire Down – 09.00 Friday 23rd June
Take a look at the full livestock schedule here.

This June 2023, MerlinVet Export is celebrating 10 years of MerlinVet supplying quality pharmaceuticals globally.

Since 2013, MerlinVet Export was launched as we expanded our operations outside of the UK and began exporting veterinary products worldwide, benefitting practices from Oman to Hong Kong.

To mark 10 years of MerlinVet Export, we’ll be running a special giveaway at London Vet Show on 16th – 17th November, which we’ll be announcing slightly later on in the year. For updates and further news, keep your eyes on our social media pages and make sure you’re signed up to our newsletter:

With temperatures forecast to remain high throughout the UK, there’s no better time to make sure you’re well aware of the potential risks to animals and how to keep them safe this Summer. Below we run through some tips and advice to keep different types of animals safe in the warmer weather.

General Pet Advice:

  • Don’t leave pets in your car or conservatory
  • Use pet-safe sun cream to protect your pets’ skin
  • Put out damp towels for them to lie on
  • Provide plenty of shade and constant access to fresh water (put some ice cubes in there too to keep it cool – an added bonus is that many animals love eating them)

Advice for Dog Owners:

  • Don’t leave dogs in your car, conservatory, caravan or outbuilding. If you see a dog in a hot car, call 999.
  • If you are driving and bringing your dog, think about travelling during cooler times of the day and arrange to take breaks.
  • Apply pet-safe sun cream to the exposed areas of your dog’s skin, including their ears and nose (white-furred dogs are particularly prone to sunburn).
  • Ensure there is plenty of access to shade and fresh water (ice cubes in the water bowl can be a nice treat for your dog) – take water out with you when leaving the house with your dog.
  • Provide a cool mat or damp towels to lie on (but don’t wrap the towel over your dog); if your dog loves splashing around then paddling pools and sprinklers can also be a fun way for them to cool down.
  • Groom your dog regularly to ensure their coat is lighter.
  • Walk your dog in the morning or evening to prevent their paws from burning and to reduce risk of heatstroke; check the temperature of the pavement with the back of your hand for 5 seconds and if it’s too hot for you, it will undoubtedly be too hot for your dogs’ paws. Signs that your dog has burned pads include licking/chewing their paws, darker coloured pads or any missing parts to the pad, blisters/redness, and refusing to walk or limping.
  • Avoid running or cycling with your dog when it’s hot.
  • When walking (avoid the hottest times of the day) make sure there is always access to shade, water, and a cool surface for their paws, such as grass.
  • Dogs more likely to suffer from heat exhaustion or to struggle during walks in the warmer weather include flat-faced breeds, dogs with thick coats, overweight dogs, very old or very young dogs, and dogs with heart problems or respiratory disease – remember that ultimately, any dog can be affected.

Learn the signs of heatstroke to keep your dog safe:

  • Excessive panting, heavy breathing or difficulty breathing
  • Excessive drooling
  • Red or purple gums
  • Heightened pulse
  • Glassy eyes & fearful expression
  • Lethargy and lack of coordination or seizures
  • Collapsing or vomiting & a reluctance to get back up afterwards

If you see a dog suffering from heatstroke, they’ll need to have their body temperature lowered by:

  • Ensuring the dog is in a shaded area
  • Pouring cool water (tap water 15-16°C) over the dog – avoid extremely cold water as it could shock them; continue to pour water over them until their breathing begins to settle
  • Placing wet towels under the dog ONLY in mild cases – in more extreme cases pouring water over them is the best option
  • Providing water for the dog to drink in small amounts
  • Avoiding pouring water over their head to reduce the risk of them drowning
  • When you have cooled the dog down, ensure you take them to your nearest vet

Advice for Cat Owners:

  • Don’t leave cats in your car, conservatory, caravan or outbuilding; also make sure you check sheds, greenhouses, and summerhouses for cats before closing them
  • Apply pet-safe sun cream to the exposed areas of your cat’s skin, including their ears and nose
  • Ensure plenty of access to shade and fresh water (ice cubes in the water bowl can be a nice treat for your cat)
  • Provide damp towels to lie on
  • Groom your cat regularly to ensure their coat is lighter
  • Leave your windows & doors ajar (if it is safe to do so – for cats which stay indoors make sure these have locking mechanisms) – this will allow a breeze throughout the house

Ticks:

Ticks are small, grey-brown parasites that suck blood from other animals (and humans!) with 6 or 8 legs, growing in size and darkening as they fill with blood. They climb or drop onto your pet’s coat when they brush past them, which can commonly occur when in woodland or grassland.

It’s important to remove ticks from your pets as soon as you notice them as they can carry diseases, such as Lyme Disease. Check your dog after returning from a walk – they’re big enough to spot by eye, but you can also run your hands over their body, particularly around the head, neck, ears and paws, to check for any small lumps that indicate the tick’s presence. Upon removal, it’s crucial to avoid squeezing the tick’s body or leaving the head in your pet’s body, as this can increase the chances of disease transmission. Therefore the best approach is using a tick removal tool (easily found in pet shops or vets), slowly pushing it under the tick, and twisting the tick clockwise until it comes loose. You should dispose of the tick in some tissue and flushing it down the toilet.

You can prevent ticks from biting your pets through tick treatments which kill or repel ticks once they attach themselves to the pet’s fur. You can ask your vet for more information about this. Never use cat tick medicine on dogs or dog tick medicine on cats – this can be fatal. If a tick has fed on your pet for a number of days, they’ll drop off but they may have transmitted a disease in this time. Lyme disease is one such infection which can be extremely serious – symptoms include depression, fever, lack of appetite, lameness and lethargy, swollen joints and swollen lymph nodes. It can be treated by antibiotics if caught early – contact your vet immediately if you suspect that your dog or cat has Lyme disease.

Advice for Rabbit/Rodent Owners:

  • Don’t house rabbits or rodents in your conservatory, greenhouse or glass buildings
  • Keep cages/hutches/runs out of direct sunlight
  • Provide extra drinking water and plenty of shade in their enclosures
  • Open windows for pets that live inside – this will allow a breeze to keep them cool
  • Regularly groom your rabbit/rodents
  • Spray water on the ground or gently mist your rabbit’s ears if they’re happy for you to do so
  • Frozen water in plastic bottles wrapped in a towl can be a good way to cool down your rabbit as they lie against them
  • Regularly (twice a day) check for signs of flystrike, especially around their tail and back end (make sure to clean this area often) – to additionally minimise the risk of flystrike, clean out their enclosure including toilet area (daily), bedding (weekly), and insect-proof any outdoor enclosures
  • If you think your rabbit, hamster, guinea pig or other pet rodent is suffering from heatstroke, move them to a shaded area, wrapping them in a damp towel, and calling your vet
  • Allow your rabbits and guinea pigs to supervised outdoor access in the garden (remove any hazards beforehand)

Advice for Horse Owners:

Horses are very much prone to dehydration and ultimately heat exhaustion or heatstroke as they often spend a lot of time outside in the sun. Some tips for keeping your horses cool and hydrated are below:

  • Provide plenty of water – horses need around 55 litres of water every day, but this increases during warmer weather. Automatic watering systems or full troughs of water are recommended. Horses need to sweat to keep cool – they require constant access to water to replace the large amounts of sweat they produce. A salt lick can help replace salts lost from sweating.
  • Provide constant access to shade.
  • Apply child-safe factor 50 suncream to horses with pink areas of skin (such as on the face).
  • Choose to ride your horse during cool times in the day i.e. in the morning or evening.

Signs of horses struggling from the heat include fast breathing and heart rate, lack of appetite and not drinking, lethargy, urinating less, and muscle spasms. You can tell if your horse is dehydrated by performing a quick examination of their gums – they should be pink, shiny, and moist. If they’re dry, pale or tacky then they could be dehydrated. If your horse is suffering from heat stroke or heat exhaustion then you should move them to a shaded area and pour water over them. Crucially, make sure you call your vet for advice.

Advice for Farmers & Livestock Owners:

  • Provide ample shade & fresh water
  • Keep their living areas well-ventilated
  • Use fans to reduce heat
  • Minimise the number of animals in living areas to help air circulate
  • If cattle are brought inside, provide unlimited water, milk cows later in the day when the temperature has dropped, cool animals down with water, and feed them at either end of the day
  • Pigs are prone to heat stress so make sure: they have wallows available to lose heat; their arcs are well-insulated; misting is installed; and if necessary, hose down pigs to cool them quickly – call your vet if you think they’re suffering from heat stress
  • Keep an eye on newly shorn sheep as they are more likely to suffer heat stress than fully fleeced sheep – the fleece acts as insulation against heat
  • Don’t transport farm animals during hot weather periods – if required, move them at night when the temperature has dropped

Much of this advice comes from the RSPCA. You can find out more and get further advice by visiting their website here.