What is it and how do we measure it?
Simply said, heat stress is the inablilty of the body to expel of access heat. We humans sweat but not all animals have that ability. At Dayboro Weather we calculate the heat stress and represent it in a Modified Discomfort Index (MDI). MDI = 0.75*Tw + 0.3*Ta Where Tw = Wet Bulb Temperature and Ta = ambient Temperature. That tells us how uncomfortable things are.
At 7am this morning some values we collected in relation to heat where:
$feelslike = ’30’; // Shows heat index or humidex or windchill (if less than 16oC)
$MDI = ‘27.9’; //Modified discomfort index
$heati = ‘29.6’; // current heat index
$windch = ‘26.8’; // current wind-chill
$humidexcelsius = ‘38.8’; // Humidex value in oC
$apparenttemp = ‘31.2’; // Apparent temperature
$apparentsolartemp = ‘36.6’; // Apparent temperature in the sun
$apparenttempc = ‘31.2’; // Apparent temperature, °C
$apparentsolartempc = ‘36.6’; // Apparent temperature in the sun, °C
$THI = ‘76.9’; //Heat stress calculation (oC)
$HLI = ‘35.3’; //Heat stress load (used with Cattle), gust windspeed used (oC)
$HLIAvwind = ‘%HLIAvwind%’; //Heat stress load (used with Cattle), average windspeed used (oC)
This shows it is going to be a hot day…. for us people, but more so for cattle and animals. Their inability to cool down goes up with when the Humidity increases, the same applies to most animals.
Long story short…… your temperature gauge on the wall is not showing how “dangerous” it can be for animals. Use your “guts”, if it feels sticky then it is very very hot for animals…..
It is a term often used, but not often understood, the bigger problem is that when you notice it you are a bit to late…..
With the hot summer months in full force, heat stress in cattle is a big concern. Heat stress can cause all kinds of problems, including reduced breeding efficiency, milk production, feed intake, weight gains and even death. However, your cows and your pocketbooks don’t need to be victims to the heat. Here are five tips for minimizing heat stress in cattle from Stephen Boyles, Ohio State University Extension beef specialist:
1. Make sure cows have access to cool, clean drinking water.
It is thought that water temperature affects rumen temperature, and thus blood temperature, which affects brain centres that control feed consumption. Above-ground water lines should be provided shade by having taller grass cover them. Run lines in fields or under fences that are not being currently grazed. You should at least check the water temperature in water troughs throughout the summer. A jump in the outside temperature of just 5°C-15°C can increase total water requirements by 2.5 times. So keep an eye on that.
If you do not have an automatic water system, you should keep evaporation into account as that will be high in the early morning.
2. Rethink your rotational grazing strategies.
Producers using management intensive grazing might consider several options.
One option is to rotate through fields at a more rapid rate.
Taller grass tends to be a cooler surface to maintain cattle on than pastures with shorter grass stands.
Another option is to rotate cattle in the evening rather than the morning. The assumption is that the grass will be consumed in the evening and the ‘heat of fermentation’ or digestion is mostly dissipated by mid-morning, thereby reducing the heat load produced by the animal.
Another possible option is to graze paddocks that allow access to temporary shade or trees during the heat of the day. This will reduce equal distribution of manure throughout the paddock but might be a suitable compromise during excessively hot weather.”
3. Know that hot weather lengthens the estrus cycle.
Hot weather can reduce the duration and intensity of the estrus (heat) period, and increase the interval between estrus periods (the estrous cycle).During the early stages of pregnancy (fertilisation to implantation of the egg into the uterine wall), the embryo is directly affected by maternal body temperature. High temperatures can cause the non-implanted egg to be expelled. Implantation is estimated to occur 11-40 days after breeding. Expulsion of the embryo due to heat stress does not affect fertility of future estrous cycles but delays when she will calve again. This may be the reason we observe longer estrous cycles during hot weather.”
4. Handle cattle early in the morning.
Bulls and finished cattle are especially vulnerable to handling during the heat of the day.
Handle cattle quietly because once they get excited it will take 20-30 minutes for their heart rates to return to normal.
When hauling cattle, load early in the morning and don’t stop during the heat of the day.
5. Have an emergency plan in place for handling extreme heat.
“Emergency management generally involves wetting down the cattle and perhaps the roofs of buildings,” Boyles says. “Delivering large droplets of water (versus a mist) is preferred at 20- to 30-minute intervals. This will allow for some cooling affect. The benefits of sprinkling may not be realized if it increases the amount of mud and humidity in the feedlot.”
In the midst of the many concerns that can plague over the summer months — flies, weeds, foot rot, pneumonia, sunburn, lumps, down fences, broken down balers, etc. — don’t forget to watch for heat stress in cattle.