Let me introduce you to ROBERTA.

Roberta is the name of one of my cows, she is my MDI’er telling me when it is to hot to play outside, there is no direct relationship with any of the Roberta’s in Dayboro town or even the Dayboro District. The name was purely chosen based upon random selection. We have a very rigorous name selection process. For example “Little Roy” is named after Roy (my neighbor). We produce predominantly bulls (pretty much because the author if this article writes a lot of that) we figured we call the next one “Little Robby” (after Roys son-in-law) as it so happens it was a heifer, so it is now called Roberta. Why call cattle after names in the neighborhood? Simple… if we yell out the cows name…. it confuses the “sh.t”s out of the neighbors. Enough about that now…. 

Dayboro - mdi - RobertaHeatMDIChart - MDI The Cow knows it all.

What does Roberta do.

Roberta shows you how she feels, whilst you enjoy the comfort of your house, and here is why. Dayboro is a town that is surrounded by mountain ranges, it is almost like it is a volcano… most likely it is just a, less sexy, giant sinkhole. The real issue is that the Heat Index is going up relatively fast due to it… So lets have a look at MDI, this we use instead of Heat Index, both you can see as a “magic number” (yes another one, FBRFI is also a magic number).

MDI (Modified Discomfort Index)

So lets get complicated, MDI is calculated as  MDI = 0.75*Tw + 0.3*Ta.  Where Tw = Wet Bulb Temperature and Ta = ambient Temperature this will give us a magic number called MDI. At Dayboro Weather we associate the MDI directly with the heat stress in cattle, but it should be used for any other animal (including people). I have a particular interest in the cattle side of things, as I want them to be comfortable and looked after. It is called husbandry, I have no idea why, but it is what it is.

Cows do not sweat very well.

Cattle are unable to dissipate their heat load efficiently. Their sweating mechanism is poor and they rely on respiration to cool themselves, this is also why you do not have any specific deodorant stick for cattle. A further disadvantage is the fermentation process within the rumen generates additional heat that cattle need to disperse. As they cannot get rid of heat effectively they accumulate a heat load during the day and dissipate heat at night when it is cooler. During the weather conditions we have here in Dayboro with insufficient environmental cooling at night cattle will accumulate heat that they cannot disperse. Making it a bit harder for them the next day, this can cause a chain reaction if you like. We are lucky here, we have the Dayboro Doctor coming through in the afternoon, it is a cool(ish) breeze from the ocean which is funneled through a gap in the mountain range, this causes a “mini jet-stream”. It cools the whole area off, and makes the house temperature drop by 5C. This is also why we build the house the way it is (but that is another story).

Typical visible signs of Heat Stress

Now we know all of that, how do we know if Roberta gets hot and flustered? There are some tell tale signs.

  • Bunching (in the shade if it’s available, and ideally with a breeze so the area is not heating up),
  • Slobbering,
  • High respiratory rates (panting),
  • Open mouth breathing,
  • Lack of coordination, and trembling.
  • Seek shade or align themselves with the sun if there is no shade.
  • Splash water if it is available.
  • Eat and ruminate less.
  • Become unresponsive, lie down and start to die when their body temperature reaches 41.5°C.
  • Thirst is increased. Drinking water intake increases markedly, an indication a cow drinks 15 liters per 100kg approx on hot days.
  • Decreased activity.
  • Agitation and restlessness.
  • Increased urination (with heavy electrolyte loss, this is a big big issue. It can causes a cow to go into distress. Recently in the area we had a cow die because of it. Heat stress, bit of bacteria infection (cocci) and heavy loss of body fluids. If you cow is in that shape, only on thing you can do is give it Gatorade or some sort of sports drink. To increase the electrolyte)
  • Crowding over the water troughs.
  • Refusal to lie down.
  • Slower growth rates.
  • When the relative humidity exceeds 50%, the dissipation of heat by evaporation cooling becomes much more difficult and signs of heat stress develop sooner. This is typical for our area, due to the high humidity, this is also why I decided to use MDI.

So for that reason… the image shows a cow… simple right… 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  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.