mingiz
Horse Poor
Got this from a friend...
From an article about the death Saturday night of a horse in a show in Tennessee:
Add air temperature and relative humidity and subtract wind speed if your total adds up to 180 or above don't ride, if it is 130-170 use caution, 130 or below...ride!
Temperature (F) + relative humidity (%) # - wind speed (MPH)
For example:
Temperature (F) 79
Relative Humidity 58 (%)
Wind Speed 4.6 (MPH)
Answer = 132.4
Less than 130: All go - #horses can function to cool themselves assuming adequate hydration.
130 -# 170: Caution - #a horse's cooling mechanisms can only partially function as intended. Some cooling management procedures will need to be performed.
180 or above: Stop# - a horse's cooling systems cannot and will not function adequately. All cooling procedures will need to be utilized to keep the horse out of serious trouble.
Why is it an issue for the horse when heat and humidity combine to equal 180+? What doesn't work and why? What are some of the physiological ramifications? What are some of the symptoms?
Heat is produced by muscles in the metabolic conversion of chemical energy to the mechanical energy required for muscle contraction and limb movement. Seventy-five to eighty percent of the chemical energy is converted to heat, which moves from the contracting skeletal muscles to the surrounding tissues by the flow of lymph and blood.
Assuming a comparable rate of exercise intensity, the rate of cooling, or heat loss is affected by air temperature, wind velocity and humidity. (Werner, 1993). Heat can also be lost in a fourth way, conduction, which is a direct transfer of heat from the skin or feet to surfaces in direct contact (such as an ice bag on the skin).
So, thinking about the chart and the equation:
Temperature (F) + relative humidity (%) #- wind speed (MPH), we see how the ability of the horse to cool itself in these four different ways will be affected:
In cool temps with low humidity, heat loss through convection and conduction can be as much as 50%. Heat can also be lost through radiation, with as much as 60% of a body's heat lost in this way when air temperatures are cool. The numbers in our equation would add up to much less than 180, and the horse would have no difficulty cooling itself.
As temperatures rise, the thermal gradient for heat dissipation is reduced, resulting is less convective, conductive and radiative heat loss and more evaporative cooling. The evaporation of water from the skin surface is the most important means of heat dissipation in high-heat/low-humidity conditions. So, when we get a high temperature
reading with low humidity, a horse may still not have difficulty cooling, but if temperatures are extremely high with no wind, we might get a result above 140, which would means our horse needs our help cooling off.
With high humidity, sweat cannot evaporate as easily and so the ability of the horse to cool itself in this important way is reduced. When high humidity is combined with high temperatures, (which we just saw reduce the effectiveness of radiant, conductive and convective cooling), the horse has now lost all four means to cool itself and is in a dangerous situation, subject to a greater rate of heat accumulation within his body.
From an article about the death Saturday night of a horse in a show in Tennessee:
Add air temperature and relative humidity and subtract wind speed if your total adds up to 180 or above don't ride, if it is 130-170 use caution, 130 or below...ride!
Temperature (F) + relative humidity (%) # - wind speed (MPH)
For example:
Temperature (F) 79
Relative Humidity 58 (%)
Wind Speed 4.6 (MPH)
Answer = 132.4
Less than 130: All go - #horses can function to cool themselves assuming adequate hydration.
130 -# 170: Caution - #a horse's cooling mechanisms can only partially function as intended. Some cooling management procedures will need to be performed.
180 or above: Stop# - a horse's cooling systems cannot and will not function adequately. All cooling procedures will need to be utilized to keep the horse out of serious trouble.
Why is it an issue for the horse when heat and humidity combine to equal 180+? What doesn't work and why? What are some of the physiological ramifications? What are some of the symptoms?
Heat is produced by muscles in the metabolic conversion of chemical energy to the mechanical energy required for muscle contraction and limb movement. Seventy-five to eighty percent of the chemical energy is converted to heat, which moves from the contracting skeletal muscles to the surrounding tissues by the flow of lymph and blood.
Assuming a comparable rate of exercise intensity, the rate of cooling, or heat loss is affected by air temperature, wind velocity and humidity. (Werner, 1993). Heat can also be lost in a fourth way, conduction, which is a direct transfer of heat from the skin or feet to surfaces in direct contact (such as an ice bag on the skin).
So, thinking about the chart and the equation:
Temperature (F) + relative humidity (%) #- wind speed (MPH), we see how the ability of the horse to cool itself in these four different ways will be affected:
In cool temps with low humidity, heat loss through convection and conduction can be as much as 50%. Heat can also be lost through radiation, with as much as 60% of a body's heat lost in this way when air temperatures are cool. The numbers in our equation would add up to much less than 180, and the horse would have no difficulty cooling itself.
As temperatures rise, the thermal gradient for heat dissipation is reduced, resulting is less convective, conductive and radiative heat loss and more evaporative cooling. The evaporation of water from the skin surface is the most important means of heat dissipation in high-heat/low-humidity conditions. So, when we get a high temperature
reading with low humidity, a horse may still not have difficulty cooling, but if temperatures are extremely high with no wind, we might get a result above 140, which would means our horse needs our help cooling off.
With high humidity, sweat cannot evaporate as easily and so the ability of the horse to cool itself in this important way is reduced. When high humidity is combined with high temperatures, (which we just saw reduce the effectiveness of radiant, conductive and convective cooling), the horse has now lost all four means to cool itself and is in a dangerous situation, subject to a greater rate of heat accumulation within his body.
