Pourquoi les membres de mon cheval sont froids? - Why the cold legs?

🇬🇧 English version
Quel est le problème? Circulation sanguine périphérique temporairement réduite, membre hypothermique. Un membre froid ou plusieurs membres froids.

Est-ce vraiment un problème? Pas forcement...
Est-ce qu'il est mal vascularisé? Pas si c'est temporaire...
Est-ce qu'il a une lésion nerveuse? Probablement pas si c'est temporaire...
Tous les pieds/membres sont froids ou qu'un pied/membre inférieur? Si un pied est chaud - est-ce qu'il est vraiment chaud ou il est température normal et c'est les autres qui sont froids?
Le cheval est-il boiteux? - souvent non, pas de tout...

Ces membres froids sont présents plus souvent qu'on pense mais nous les voyons pas à l’œil nu, il faut toucher ou utiliser un caméra thermique... 

Avec ma caméra j'ai vu des différences de 10-13°C entre les membres perfusés pleinement et les membres hypothermiques. En tant que technicien en thermographie équine quand je regarde les membres je suis beaucoup plus méfiant envers les petits changements de température que les grands, les grands me crient la thermorégulation (même si je ne sais toujours pas si c'est le bon terme à utiliser, "coupure thermique" peut-être?). Les vrais problèmes et pathologies peuvent être plus difficiles à repérer car ils ont des subtiles différences de température, bien que quand sévère ils sont parfois visibles quand même avec le coupure thermique. Bien que je ne panique pas à propos de la pathologie quand je vois ces températures froides (j'ai l'habitude de voir ces images maintenant), je pense que ce sont des informations fascinantes qui me donnent des indices sur la façon dont le cheval utilise son corps et son état physiologique. (Ces images sont vues habituellement quand la température ambiante est base.) 

Pour les séances d'images thermiques, si nous trouvons cette situation, si possible il faut faire marcher le cheval pendant 15-20 minutes pour que la perfusion revienne. La température ambiante idéale pour les séances est entre 20-25°C pour justement augmenter la chance d'avoir plein perfusion dans les membres.  Continuez à lire cet article pour voir mes idées sur le "pourquoi" nous voyons ces membres froids et les solutions potentielles.

J'ai plus d'images, rejoignez le défi d'observation de la température pour les voir dans ma vidéo présentation informelle (et oui un peu longue).

"Le critère FEI est une différence de deux degrés (Celsius), mais la recherche a montré qu'une différence d'un degré (Celsius) sur 25% des zones symétriques est cliniquement significative (pathologique). Lors d'un examen, je recherche une différence subtile de 1/3 degré (Celsius) comme indice de suspicion pour inspecter les problèmes potentiels." Dr Tracy Turner DVM

Quelle est la cause?
  • Vérifiez la température du corps, le cheval a-t-il froid?
  • Réponse thermorégulatrice au flux de sang capillaire, shunts directs, shunt artérioveineux, arteriovenous anastomoses (AVAs)? [Pollitt]
  • Est-il debout sur une surface dure [bowker]
  • Est-il immobile?
  • Le pied ferré - la pression sanguine dans le pied sera plus élevée, donc pas autant de perfusion des tissus. Un pied ferré sera plus froid qu'un pied nu. [Bowker] (J'ai des images dans ma présentation des pieds ferrés perfusés et non perfusés, le même cheval avant et après 20 minutes d'exercice)
  • Portance du poids inégale liée à l'asymétrie ou la posture?
  • Portance du poids inégale liée au blessure/abcès?
  • Est une vrai diminution de circulation ou es temporaire? si pas de blessure ni boiterie, le flux revient-il avec le mouvement?
  • Vasoconstriction via le système nerveux sympathique? (La vasoconstriction induite par l'adrénaline pourrait contribuer à une résistance vasculaire élevée) (La réponse à la stress pour garder la circulation vers les organes vitaux et les muscles de fuite/se battre...)
  • Muscles contractés liées à l'activation du système nerveux sympathique? (Avec la principe que les muscles contractés ne laisseront pas passer le flux sanguin, je pense que c'est différent de celui ci-dessus)
  • Perte d'approvisionnement vasculaire? - vérification avec vénogramme
  • Une lésion nerveuse? une lésion nerveuse due à un traumatisme ou à une maladie affecte le flux sanguin et peut apparaître "froide" (bien que la prévention de la conduction nerveuse par l'utilisation de blocs nerveux chimiques ou chirurgicaux entraîne une augmentation de la température de la surface du corps [Purohit] )
(De la chaleur dans les pieds - avec augmentation du pouls digital - vient avec un abcès, l'ecchymose, la fourbure...)

Donc quand nous considérons ces chevaux avec les membres froids il faut qu'on demande: Ils ont froid? Ils ont des pieds chauds ou froids? Ils sont en activation sympathique? Ils sont debout sur un sol dur? Ils manquent du mouvement? Puis on peut demander combien de temps ils sont dans cette état, par exemple le cheval hébergé au boxe 23h, combien de d'heures par jour ses membres inférieurs seront bien perfusés? Est-ce cela signifiant? Quelles sont les implications éventuelles? (Je n'ai pas dit que j'avais toutes les réponses... je propose quelques solutions plus bas.)

Est-ce un des raisons pourquoi les pieds poussent moins pendant l’hiver? ils ne sont pas bien « irrigués »?  

Les solutions:  
  • s'il y a une boiterie avec ou sans asymétrie dans le modèle thermique, c'est le vétérinaire qu'il faut appeler!
  • attendez une temps plus chaud (!) - s'il fait froid et votre cheval fait une thermorégulation, pour moi il n'y a pas de problème!  (Par contre si votre cheval a vraiment froid, peut mal tolérer de perdre du poids et n'a pas de couverture ou accès au foin à volonté je commencerai par faire ces modifications)
  • plus de mouvement (exercice)
  • changez l’environnement pour que le cheval bouge plus et ne reste pas sur du béton (moins de temps au boxe, paddock paradise, tapis en caoutchouc dans les abris, etc)
  • le déferrage peut augmenter la circulation dans les pieds (le déferrage n’empêche pas d'avoir les membres froids - beaucoup de mes exemples dans la présentation disponible dans le "température observation challenge" sont des pieds nus - mais ils vont le faire moins souvent et ils seront pas si froids...)
  • bodywork - pour travailler la symétrie ou le sur activation de la système sympathique, ou quand vous ne pouvez pas bouger votre cheval suite au blessure par exemple, vous pouvez utiliser les modalités de toucher pour promouvoir la circulation vers les pieds: Tellington TTouch, Sure Foot coussinets de stabilité, Shiatsu, Massage, Ostéo… 
❔ Voir la girafe


Une expérience avec ma caméra thermique

Ce cheval était au repos dans un abri avec du sol en béton. Ses antérieurs étaient en état de thermorégulation (circulation du sang réduit dans les membres inférieurs, rappelez-vous qu'il n'y a pas des muscles dans le membre inférieur...), voici ce qui se passe quand il passe du temps sur les coussinets de stabilité Sure Foot.


Plus d'infos sur la Thermographie



C'est les muscles qui contrôlent le flux sanguine dans le pied... une présentation qui est bien relevant à cette discussion.


Coin à Lire


Le Coin à Lire n'est qu'en anglais pour le moment mais c'est bon! Voir plus bas...

Je revisiterai cet article plus tard peut-être, j'apprends plus sur ce sujet tous le temps, comme beaucoup de mes articles ça sert comme référence pour moi.

Les images ici sont fournies en tant que information, l’interprétation des images thermiques devrait prendre en compte plusieurs éléments. En aucun cas un diagnostic sera proposer dans une séance thermographie équine.  Uniquement un vétérinaire aura autorité. 


🇬🇧

Why the cold legs?

What is the problem/issue?
temporary reduced blood circulation (and therefore heat pattern) in the peripheral limbs - cold legs

Is it actually a problem? Not necessarily....
Is there a circulation problem? Not if it's temporary...
Is there a nerve problem? Probably not if it's temporary...
Are all four feet/legs the same temp? if 1 or 2 hot - are they really - or are the others cold?
Is the horse lame? - very often not.... 

This cold leg state is very common but you can't see it without touching or using a thermal camera. 
With my thermal camera I've seen 10-13°C differences between perfused limbs and hypothermic limbs.  As an equine thermography technician I'm far more suspicious of small temperature changes than large ones, large ones scream thermoregulation to me (although I still don't know if this is the right term to use, "thermal cut off" is another name). The real problems and pathologies can be much more difficult to spot because they have subtle differences in temperature, though the more severe ones will sometimes show through the thermal cut off.  While I don't panic about pathology when I see these cold temperatures (I'm used to seeing these images now) I do think it is fascinating information that gives me a clue as to how the horse is using his body. (These images are seen normally when the ambient temperature is low). 

For thermal imaging sessions, if we come across this, if possible we will exercise the horse for 15-20 minutes to get the circulation back in the limb. The ideal ambient temperature for an imaging session is 20-25°C which increases the chance that the limbs will be fully perfused for imaging.  Keep reading this article for my ideas on why we see these cold limbs and potential solutions.

I've got more images, join the Temperature Observation Challenge if you would like to see them, there is a video presentation (it's currently in French, if you would like me to do it in English let me know).

"FEI criteria is two degrees (Celsius) difference, but research has shown that a one degree (Celsius) difference over 25 percent of symmetrical areas is clinically significant (pathological). During an examination I look for subtle difference of 1/3 degree (Celsius) as an index of suspicion to inspect for potential problems." Dr Tracy Turner DVM

These are some of my older images, they are not normalised
for a thermal imaging report but set at a scale that illustrates
the subject at hand.
What is the cause?
  • Check their body temperature, are they feeling cold?
  • thermoregulatory response to capillary blood blow, direct shunts, arteriovenous shunting, arteriovenous anastomoses (AVAs)? A normal function of dilated AVAs may be to maintain foot temperature above the tissue freezing point [Pollitt] 
  • Are they standing on hard ground [bowker]
  • Are they standing still?
  • Shod foot? - pressure inside the foot is going to be higher, not as much perfusion of the tissues.  A shod foot is going to be colder than a barefoot.  [Bowker] (I have thermal images of a horse in shoes showing fully perfused and reduced perfusion situation in my presentation - the same horse before and after 20 mins of exercise)
  • Unequal load bearing related to asymmetry or posture? 
  • Unequal load bearing related to injury/abscess?
  • Is it true low blood circulation or temporary reduced blood circulation? If there is no injury or lameness, does it go away/return to normal with movement?
  • Vasoconstriction from the sympathetic nervous system? (the stress response reduces blood flow to the extremities prioritising vital organs and muscles needed for flight/fight)
  • Contracted muscles from activation of the sympathetic nervous system? (With the idea that contracted muscles don't let blood flow, I think it is different to the one above)
  • Loss of vascular supply? - venograms will verify
  • Nerve injury? nerve damage due to trauma or disease affects blood flow and may show up "cold" (in research preventing nerve conduction by the use of chemical or surgical nerve blocks results in increased body surface temperature [Purohit])
(Heat in the feet comes with digital pulse increase often from: abscess, bruising, laminitis...)

So when considering horses with these cold legs we have to ask: Are they cold? Are they in sympathetic activation? have they been standing on hard ground? are they lacking movement? Then perhaps consider how much time they spend in that state, for example a horse stabled 23h per day, how much perfusion does he get to his feet in a day and how important is that?  What are the implications if any? (I didn't say I had all the answers... I have some suggestions for potential solutions a little further down.)

Is this one of the reasons why hooves grow less in winter, they spend less time "irrigated" with blood circulation?

The solutions:  

  • if the cold heat pattern is asymetric and/or accompanied by lameness, call the vet!
  • wait for it to get warmer (!), if it's cold and your horse is thermoregulating, for me there isn't a problem! (but if the horse is really cold and can't afford to lose weight and isn't rugged or eating unlimited quantities of hay, I would start by changing that...)
  • more movement (exercise)
  • change their environment so that the horse moves more in it's everyday life and isn't standing on concrete for long periods (less time in a stable, paddock paradise system, rubber matting in the shelter, etc)
  • go barefoot (this won't prevent the horse's legs from getting in this cold state - lots of the examples in my presentation in the "température observation challenge" are barefoot - but they will do it less often and won't go quite so cold)
  • bodywork - to work on assymetries or an over stimulation of the sympathetic nervous system or if you can't move your horse because it's injured or in rehab, you can use touch to promote circulation in the legs and feet: Tellington TTouch, Sure Foot balance pads, Shiatsu, Massage, Osteopath…
❔ See the giraffe

An experiment with my thermal camera

This horse was resting in a shelter with a concrete floor.  His front legs were in a state of thermoregulation (reduced blood flow in the lower limbs, remember that in the lower limb there are no muscles...), this is what happened when he spent some time on the Sure Foot balance pads.

More info on Thermography



Reading corner


"The optimal ambient temperature for imaging is 20 degrees C - 25 degrees C.  Below this temperature the distal aspect of the limbs are more prone to thermal cut off and above this range the contrast between the horse and the background is lost." p266
Diagnosis and Management of Lameness in the Horse, Michael W. Ross, Sue J. Dyson

"Thermographic evaluation of the foot and distal limb is also complicated by the thermoregulatory role of the distal limb, whereby the blood supply can be dramatically reduced to conserve heat in cold conditions.  Thus un understanding of the physiology of the distal limb is essential for optimal image interpretation." p167
"Thermoregulatory cut-off can be quite variable, and there will be intermittent periods of vasodilation.  This is not necessarily symmetrical between left and right, nor between front limbs and hindlimbs.  Re-evaluation of the horse some hours later may yield a different image, especially if the horse can be placed in a heated box.  Exercising the horse for approximately 20 minutes, as well as administration of vasodilators such as acepromazine, can also be used to increase peripheral blood flow and temperature to allow improved diagnostic imaging." p 169
"Thermoregulatory cut-off of the distal limb dramatically reduces the temperature and thus the contrast within the feet such that subtle lesions may be missedSevere inflammation in the presence of thermoregulatory cut-off will, however, still cause a sufficient increase in blood flow to be detectable." p169
Equine Podiatry, Andrea Floyd, Richard Mansmann

Equine laminitis: its development coincides with increased sublamellar blood flow - C. C. POLLlTT and C. T. DAVIES
Shunting of blood away from the nutrient capillaries of the hoof lamellae via inappropriately dilated arteriovenous anastomoses (AVAs) has been proposed as a pathophysiological mechanism for developmental equine laminitis.
A normal function of dilated AVAs may be to maintain foot temperature above the tissue freezing point (about -l.O°C) when extremely low environmental temperatures could cause damage (frostbite) to horses standing, for long periods, in ice and snow. For this to occur it is assumed that a dual circulation exists: a slow nutrient capillary circulation supporting the metabolism of the lamellar tissues and a fast AVA circulation periodically delivering warm arterial blood to the dermis of the foot when the foot reaches a critically low temperature. A circulatory arrangement like this has been described in the feet of cold adapted mammals, the arctic fox and
grey wolf (Henshaw et al. 1972). Skin AVAs are also heat dissipating structures and dilate in response to rising core temperature therefore increasing the rate of surface heat loss.
The AVAs in the digit of the equine foot may also be involved in heat dissipation, dilating in response to rising core temperatures. Partitioning of blood from one circulation to the other implies the existence of sophisticated reflex and local control mechanisms reviewed by Hales and Molyneux (1988). Sensory, afferent nerves relay information from the foot to the hypothalamus about the thermal status of the foot and in turn vasomotor, efferent nerves regulate AVA tone via catecholamine and peptidergic fibres innervating smooth muscle cells in the AVA wall.
https://beva.onlinelibrary.wiley.com/doi/pdf/10.1111/j.2042-3306.1998.tb05131.x

The Hoof Mechanism Revisited
Professor Christopher Pollitt BVSc PhD
https://mediatheque.ifce.fr/doc_num.php?explnum_id=24785

Supporting Limb Laminitis: Learning How to Save Horses Such As Barbaro - The Horse.com
There are five major forces at play in the equine hoof when the horse is standing:

  1. The horse’s weight pressing down the column of bones in the horse’s limb (gold arrow);
  2. The upward ground reaction force that counters the horse’s weight (red arrow);
  3. The rearward pull of the deep digital flexor tendon running down the back of the limb and attaching on the bottom of the third phalanx bone (green arrow);
  4. The laminae holding the third phalanx forward against the hoof capsule, against the pull of the deep digital flexor tendon (blue arrow); and
  5. The forward and upward pull of the extensor tendon running down the front of the leg and attaching to the top of the third phalanx bone (purple arrow). It plays a role in extending the leg and counteracting the pull of the deep digital flexor tendon, but it is not a major force compared to the strength of the laminae, says Redden.

"When a horse has a catastrophic injury and he keeps moving around the stall, we think he’s not taking good care of himself," he notes. "But he’s actually taking very good care of himself because he’s keeping his feet perfused (stimulating blood flow). These horses usually show no signs of contralateral limb laminitis. On the other hand, the ‘smart’ horse standing there behaving for hours not moving–his supporting foot has no blood in it."
https://thehorse.com/127435/supporting-limb-laminitis-learning-how-to-save-horses-such-as-barbaro/

Hoof and distal limb surface temperature in the normal pony under constant and changing ambient temperatures, Mogg, Pollitt 1992
"[..] arteriovenous anastomoses (AVAs) are thermoregulatory end organs, and AVAs have been demonstrated in horse skin and in the equine hoof. AVA density was highest in ear skin and hoof corium.[..]AVAs are centrally controlled, but AVA dilation is inhibited when local surface temperatures exceed core temperature as such a temperature gradient would facilitate heat absorption rather than dissipation. In contrast, capillary blood flow is under local control, increasing in response to warm local temperatures and decreasing in response to cool local temperatures."
"Clinically detectable asymmetry in limb surface temperature appears to be a normal phenomenon under certain ambient temperature conditions and does not necessarily indicate pathology."
"To what extent the temperature changes observed in the study were the result of AVA or capillary dilation is unknown and warrants further study.  The greatest temperature changes were observed in the hoof, where AVA or capillary dilatation is high, indicating that changes in AVA flow may significantly influence distal limb surface temperatures.  AVAs have also been implicated in the pathogenesis of laminitis, and therefore hoof surface temperatures may yet prove a useful clinical indicator for this disorder."
https://onlinelibrary.wiley.com/doi/full/10.1111/j.2042-3306.1992.tb02798.x



Tension patterns in Horses - Sarah Fisher
"Cold lower legs are indicative of horses that are spooky and Flight oriented, and objects moving on the ground such as leaves or flapping plastic will cause concern to the horse with inhibited circulation to the lower leg."
https://ttouch.com/images/links/2156-TENSION_PATTERNS_IN_HORSES.pdf

Sympathetic regulation of vascular function in health and disease
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3429057/

What is the Flight or Fight Response? Can you Stop it? - article on the human response
"-- When blood vessels on the skin begin to constrict (goose bumps), it also reduces blood flow to skin helping to prevent blood loss from injury that may occur during the encounter. [..]
-- Heart rate jumps from resting at 60 BPM to a whopping 200, 250 or 300 BPM. The heart pump rate goes from pumping one gallon a minute to five gallons per minutes. Coronary arteries dilate while other arteries constrict to maximize blood pressure while veins open out to ease the flow of blood back to the heart. Blood pressure sky rockets. The knees will sometime get weak from all the blood rushing to other muscles. Fingers and toes will tingle from lack of blood, much like what happens when you get cold, the body will sacrifice outer limbs to keep blood to more important and vital organs."
http://www.thinklikeahorse.org/flight_or_fight.html


"Blood flow ensures the transportation of nutrients, hormones, metabolic wastes, O2 and CO2 throughout the body to maintain cell-level metabolism, the regulation of the pH, osmotic pressure and temperature of the whole body, and the protection from microbial and mechanical harms."
https://en.wikipedia.org/wiki/Hemodynamics

"Acute local blood flow regulation refers to intrinsic regulation, or control, of arterial vascular tone at a local level, meaning within a certain tissue type, organ, or organ system. This intrinsic type of control means that the blood vessels can automatically adjust their own vascular tone, by dilating (widening) or constricting (narrowing), in response to some change in the environment. This change occurs in order to match up the tissue's oxygen demand with the actual oxygen supply available in the blood as closely as possible.
There are several mechanisms by which vascular tone, and therefore blood flow, is controlled. The sympathetic nervous system and a variety of hormones, for instance, both exert some degree of control over vascular tone. However, the local intrinsic regulatory system described here is completely independent of these other mechanisms.[1] Many organs or organ systems have their own unique mechanism of local blood flow regulation, as explained below."
https://en.wikipedia.org/wiki/Local_blood_flow_regulation

Physiology: hemodynamics, endothelial function, renin–angiotensin–aldosterone system, sympathetic nervous system
"Blood flow and vascular resistance are markedly influenced by extrinsic stimuli including stress, trauma, hemorrhage, pain, and exercise. These conditions elicit increases in sympathetic nervous activity which directly increases vascular resistance. Strong activation of the sympathetic nerves results in marked vasoconstriction mediated by α-adrenoreceptors, leading to decreases in blood flow."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4115246/

The sympathetic release test: A test used to assess thermoregulation and autonomic control of blood flow
https://www.researchgate.net/publication/260446609_The_sympathetic_release_test_A_test_used_to_assess_thermoregulation_and_autonomic_control_of_blood_flow

Skin temperature measured by infrared thermography after specific ultrasound-guided blocking of the musculocutaneous, radial, ulnar, and median nerves in the upper extremity, June 2011
"Sympathetic blocking leads to vasodilation, increased blood flow, and, hence, an increase in tissue/skin temperature."
https://www.sciencedirect.com/science/article/pii/S0007091217331896


Continuous digital hypothermia initiated after the onset of lameness prevents lamellar failure in the oligofructose laminitis model
A. W. van Eps C. C. Pollitt C. Underwood C. E. Medina‐Torres W. A. Goodwin J. K. Belknap
https://beva.onlinelibrary.wiley.com/doi/full/10.1111/evj.12180
[DD: and so perhaps another reason why horses in acute laminitis shouldn't be moved to maintain thermal cut off and perhaps reduce the damage caused]

Prolonged, continuous distal limb cryotherapy in the horse. Pollitt, Van Eps
https://www.ncbi.nlm.nih.gov/pubmed/15147127


Horse Care; Cold Limbs Trouble Brewing?
An energetic viewpoint
https://holistichorse.com/equine-therapy/cold-legs-cold-horse-may-mean-a-problem-is-brewing/

Cooling your horse's lower legs, why? why not? and how - David Marlin
https://davidmarlin.co.uk/portfolio/cooling-your-horses-lower-legs-why-why-not-and-how/


Does Exercise Cause Vasoconstriction?
https://healthyliving.azcentral.com/happens-vessels-exercise-17621.html

Cold Legs – Causes of Lower Leg Coldness with Pain and Aches
https://www.healthhype.com/cold-legs-causes-of-lower-leg-coldness-with-pain-and-aches.html



❔ Can you spot the cold legs? Why do you think they are cold?



I might develop this article a bit later, I'm constantly learning about this issue, as with most of my articles, it serves a reference for me.

The thermal images provided here are for educational purposes. The interpretation of thermal images should take into account several factors. No diagnostic will be provided in an equine thermal imaging session, only a veterinarian has the authority to diagnose.


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