What is it, why it happens, how to prevent and solve it
What is heat stress?
Your animals digest fibre-rich food and convert it into nutrients through microorganisms. However, when the ration is too rich, they don't have enough of them to reduce the acidity due to this type of food, which leads to acidosis.
Heat stress occurs when the animal produces or receives more heat than it dissipates. As soon as the outside temperature exceeds 20° or the THI exceeds 68°, high-producing pigs, cows and chickens become “stressed”, with the consequences of impaired well-being, reduced productivity and health risks. The risk is increased when the air is very humid.
Summer temperatures are increasing
According to the french meteorological Service “Météo France”, summer temperatures will rise by around 1°C to 2°C by 2040/2060 and the phenomenon will become more pronounced at the end of our century. The herds are growing, producing more and more heat inside the building as well. (CNIEL 2019).
Climate predictions for the coming years make it likely that the frequency of heat stress duration will increase. It is therefore necessary to implement preventive measures in animal husbandry, particularly with regard to animal nutrition and housing.
Which animals are affected by heat stress?
Ruminants are the most affected animals
When the temperature is too high, ruminants' body temperature rises and they evacuate it through the respiratory tract (significant increase in respiratory rate), which leads to an increase in exhaled CO2 and respiratory alkalosis. The cow is considered to be heat stressed when her breathing rate increases to 60 per minute (compared to 15 - 35 in normal times).
This alkalosis reduces the amount of bicarbonate naturally available in the animal and therefore reduces its ability to fight ruminal acidosis. This phenomenon is accentuated by an increase in sweating leading to a loss of potassium, and an increase in urinary losses (because the cow drinks more) leading to a loss of sodium.
The result is a reduction in food consumption and rumination time, a rapid deterioration in the animal's performance and health problems such as lameness and hormonal changes: impaired fertility, unsuccessful fertilisation, embryonic death, foetal abortion, etc...
As a result, milk production decreases, as well as the butterfat content (BC) and protein (TP) levels of milk.
In the dry cow, heat stress will cause a lower milk production during future lactation.
Pigs are also subject to heat stress!
Like ruminants, the physiology and metabolism of monogastric animals are affected by temperature conditions. High temperatures cause hyperventilation of the lungs (increased respiration rate) in monogastric animals, resulting in :
- a decrease in blood bicarbonate levels and reduced performance (growth, feed conversion, sow milk production and fertility).
- increased urinary sodium loss.
In a recent interview, Dr. Calini, an expert in poultry nutrition, recalls that hens used to lay about 270 eggs in a standard production cycle in the 1980s, and that this number has now risen to 340.
This is a source of "stress" for our hens: they have fewer resting days and are more likely to suffer from high temperatures, which, among other things, hampers the proper calcification of their eggshells.
How can we reduce the impact of heat stress?
Remaining vigilant and identifying the first signs of heat stress
Signs that identify animals facing heat stress include decreased feed intake, reduced rumination (in cows), and increased respiratory rate.
Adding Bicar®Z to the ration as a preventive measure before the heat wave
Bicar®Z provides the animal with two essential nutrients: sodium to maintain an adequate electrolyte balance and bicarbonate to stabilise the ruminal pH at around 6.2.
Protect animals from heat
Good ventilation of the barn is essential. Make sure that there are shadowy areas in the field. If possible, only take the animals out at night.
There are also a number of building design features that are effective in reducing the impact of heat stress, such as :
- A strong air circulation in the buildings; look for a crossing circulation ("wind" effect); in hot periods, the objective is to have as few walls as possible; removable walls (inflated, rolled up, mobile) are to be favoured in order to manage the summer/winter gaps;
- Offer shade on the pasture; only graze at night and bring the animals in during the day (provided the building is suitable), cover the outside calf kennels with a roof;
- Use ventilation (from 20°); if necessary, put in place foggers or sprinklers, associated with ventilation; Cool the animals in the waiting areas;
- Put in place insulated roofs, which avoid heat transfer through sheet metal or fibro-cement whose temperatures can reach 60°;
Provide water in abundance
Make sure that drinking troughs are accessible and that fresh water is available.
Adapt the diet during the period of heat stress
In case of heat stress, animals consume less feed. Maintain maximum feed consumption, taking into account the quality and freshness of the feed. In case of doubt, do not hesitate to consult your feed supplier to adapt the ration.
- Moisten the ration and distribute the feed in the evening rather than in the morning: do not prepare it for the day, so that the feed is not in place for a whole day and is warm.
- For dairy cows, provide unsorted, short, sufficient, but not excessive amounts of fibre, well consumed, avoiding overly bulky rations ;
- Eliminate the feed that heats up and rejects;
- Provide niacin, which increases vasodilation and decreases body temperature.
- For dairy cows, increase the sodium level to 0.4% of the ration and the DCAB to 400 mEq/kg DM, which is equivalent to 250 g of sodium bicarbonate (and more if necessary); ensure that the potassium level is at least 1.5% of the MSI;
- For hens and pigs, increase the levels of sodium, BE and possibly potassium according to the recommendations of your nutritionist who will take into account the specificities of your production.