Plan a strategy to fight heat stress: understanding the danger that hangs over our animals
Do: refresh the stable, identifying the most suitable to your needs, the type of housing and the climatic averages
Check: verify the improvement of the welfare of the animal, both during lactation and in the dry season
Act: prevent heat stress is better than cure, when the effects have already appeared.
Heat stress in cattles is a widely known problem that starts in May and lasts until October.
In Summer, when the temperature reaches 36-37°C deaths caused by excessive temperature are common, as demonstrated by a study conducted by the Zooprophylactic Institute Emilia Romagna on a sample of 320,000 garments 2002-2007.
Also this study conducted by Viterbo University, shows that high values of temperature and humidity are a real cause of cattles mortality and as a correct policy of risk reduction “knowledge” it helps to reduce the costs associated with mortality in cattles.
The parameter to be checked
It is well known that high temperature is in relation to the rate of relative humidity: for this reason, at the same temperature, we perceive a different sensation of heat according to the relative humidity.
THI (Thermo Hygrometric Index) is the index that takes into accounts these values. This index is used since a long time for humans and cattles and provides an indication of discomfort from hot.
According to scholars, reached a certain level of THI, discomfort quickly becomes mortality. The statistics show that in fact, with a level of THI exceeding 70, the mortality of cattle increases dramatically, as if a limit of physiological endurance was exceeded.
Cattles mortality based on THI (Thermo Hygrometric Index)
It ‘obvious that if we cool cows before exceeding this limit, the cost of the mortality of cows will be minimized.
The effects of heat stress on lactation
This is another study of prof. Dahl, Department of Animal Sciences University of Florida(USA) http://dairy.ifas.ufl.edu/dpc/2012/Dahl.pdf shows that heat stress reduces the productivity of cattles in milk production.
Particularly interesting are the considerations that the risk of heat stress-related THI affects in different directions the productivity of the cow in lactation.
A first aspect, perhaps the most important, is the duration of exposure to heat: While in short situations of heat stress the negative effects express themselves in reduced milk production and falling within 24-48 hours after the event, in case of prolonged heat stress even for only 72 hours, we have negative effects for the whole lactation.
Critical THI values are exceeded for weeks, as the weather data on the Po Valley in recent decades show.
That’s why it’s important to keep the cows cool during the whole Summer season, this operation is possible only with systems of “dry” fog, which unlike the traditional hand shower, don’t wet and have no negative effects on the animal and on the stable.
Acting in advance we can reduce the decline in milk production that occurs during the Summer.
A second aspect is the physiological state of the cow. Indeed, when the cow is lactating, produces up to 50% more heat and it is consequently much more sensitive to heat and stress by high THI.
The value is reduced of 5°C compared to dry cows.
The professors of the Department of Animal Sciences University of Florida believe that the effects of THI are currently underestimated. The value of THI to above which there is a decline of lactation is 65.
With values of THI between 65 and 73, the decrease in production is, on average, 2.2 kg of milk per day.
It’s necessary therefore to cool the lactating cow (which has a daily production of 35 kg of milk) when the THI reaches a value of 65.
A third aspect to consider is the effect of radiant heat. Radiant heat is closely related to the rectal temperature and the decrease in production, and the negative effect is critical when there is an intense solar irradiation, in the absence of adequate cooling systems.
During the Summer season there is also a decrease in the percentages of fat and protein in produced milk. Less than 0.4% fat and less than 0.2% milk protein. Although this problem is caused by the high temperatures and the heat stress.
The characteristics of the area, such as proximity to the sea (which brings the classic sea breezes to cool and reduce moisture), or the possibility of staying outdoors improve the lactation curve.
The housing in overcrowded, lack of protection from direct and poor ventilation are additional factors that make heat stress worse.
The ideal temperature range for a cow in milk, is between -5°C and 23,9°C. Above the maximum value, we begin to see the first effects on production: both decrease the amount of milk, and the percentage of solids not fat, protein, lactose and fat in milk.
According to some studies conducted in the Netherlands, the temperature above which occurs the stress of cattle is 17 ° C.
The decline in milk production, up to 20%, is largely due to the reduced supply of beef, the animal eats less.
The hydration of the body is used largely for sweating in cattles; blood flow is diverted from the breasts to the peripheral circulation to dissipate the heat better.
Protect dry cows with shade and cooling systems (fans and sprayers) is used to limit losses from heat stress in the next lactation (+ 3.5 kg of milk / day, through lactation compared to cows that have only shading).
The cooling also has positive effects on the immune system of dry cows (in particular the defenses acquired) which makes them more resistant to mammary infections during the first stage of lactation.
The symptoms of heat stress
The cattle are defending themselves from the heat by perspiration and sweating, which makes it possible to dissipate the excess heat by evaporation of water from the skin. Exactly the same physical process that occurs in the human being and which regulates the mechanism of cooling by spraying.
When the heat increases, the cattle put in place strategies to reduce activities that generate internal heat (feeding, milk production, to move) and increases the activity of heat loss (sweating, increased respiration and salivation).
Heat stress can be so easily identified by observing the behavior of the animal: cows panting, sweating, are nervous, do not lie down, drink more to compensate for the sweating and eat less. Sometimes looking for mudflats and breathe with his mouth open and tongue out.
Behavioral mechanisms are very similar to those in humans, leading to a reduction in milk production and, if ignored, may lead to death of the animal.
Effects of elevated summer temperatures on bovine reproduction
Heat stress causes a reduction in the rate of conception (-20/30%), an increased risk of miscarriage during the third month of pregnancy, manifestations estrous are reduced. (Heat stress in Dairy Cattle, Annual Conference of the Australian Veterinary Association – Australia)
The main reason of this fact is the lack of food, which makes more difficult the continuation of the pregnancy of the cow.
In addition, heat stress in the last trimester of pregnancy cause up to 8% the birth of calves underweight and colostrum is of poor quality and the negative effects also affect lactation.
Even heifers experiencing heat stress have a lower body weight (up to 16%) and this adversely affects lactation.
Health effects on bovine
The humid heat favors the onset of environmental mastitis, because cows tend to lie on damp surfaces, soiled by feces, or in the mud, favoring bacterial contamination of the breast and the colonization of the teat canal.
The intense sweating leads to loss of electrolytes (sodium, potassium), not replenished with food, and breathing with difficulty due to the increase of carbon dioxide, decreased blood pH in respiratory alkalosis.
The reduction in appetite leads to a metabolic imbalance, due to lower consumption of fiber (cows prefer concentrates), the reduced chewing, with reduction of the buffer of the saliva on rumen content (the saliva is lost from your mouth open, for facilitate lung ventilation).
All this can cause sub-acute ruminal acidosis(“sara”), that predisposes to laminitis and hoof injuries.
In blood, there is a decline in growth hormone, prolacting and thyroid hormones, blood calcium decreased, blood urea increased, hypoglycemia and hypercholesterolemia.
Strategies for preventing heat stress in cattle
Preventing heat stress, rather than fight it when it is in place, the strategy is more correct, as universally established by the researchers.
There are various ideas to reduce heat stress, relate to the form of housing, the management of milking, cooling systems.
Fresh water must be easily accessible, preferably in shaded areas, near the area of nutrition, rest or milking. The water must be clean, fresh, good quality and free of impurities and microorganisms (including molds and algae).
The presence of pools or ponds allow the cows to cool properly, and were not observed apparent negative effects on milk quality and udder health, however, represent a controversial method, and are a possible source of parasites (Leptospira) and germs.
If the building is small, with the ridge of the roof closed, it is possible to cool the roof with water, or painting it with reflective paints, even if the best solution is to cool directly the animal.
Both outdoors and inside buildings, it is useful to reduce the density of animals, in particular by creating small groups in the pre-milking waiting room.
The cleaning and sanitizing of the environments and floors must be particularly accurate, because with the heat increases the risk of environmental mastitis is high
MGF solutions, misting helps to reduce heat stress
MGF misting solutions, misting systems are simple or combined with appropriately sized fans and allow to reduce the effects of heat stress.
Systems with only one nozzle can be conveniently combined with the cooling fans in the barn in order to cool the hot air coming from the roof.
Most important benefits offered by MGF ventilation and misting systems are the following:
- do not increase the environnemental moisture thanks to electronic systems that calculate THI and modulate the operation of the pump and the fan, by mixing the right amount of water in fan air
- thanks to ventilation with tilt, they promote the evaporation of the sweat by increasing the dispersion of heat
- enable you to locate cooling close to feeding passage, encouraging the animal to eat
- generating a very fine mist, without making the floor of the stable wet, avoiding in this way the proliferation of microorganisms such as parasites (leptospires) and germs.
- they can be successfully used also in waiting rooms, since the very fine mist evaporates quickly and reduces the drip on the udder, which causes infections and prevents the stagnation of dirty water, reducing the formation of bacteria
- facilitates the operations of milking, as the bovine is more relaxed
- It makes the automatic disinfection of the environments, by spraying disinfectants. The operations of cleaning and sanitizing rooms and floors must be particularly accurate, because the heat increases the risk of environmental mastitis.