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A breath of fresh air

July 12, 2011
In a barn, long and narrow like a greenhouse, tunnel ventilation brings comfort and handles the milk production of the cows during the hot summer, if the speed of the wind is adequate.
The financial losses are important. Cows can die or abort. Herds can show a lower milk production. Cases of mastitis can multiply and the count of somatic cells increases. A room temperature too high causes stress to the dairy cow which may cause lower productivity.
Effects of the wind
To refresh a cow, nothing is better than wind. Water can also help, but only it if comes in direct contact of the animal’s skin. Otherwise, the increase of the humidity in the air amplifies the heat sensation, what we call humidex. It’s better to rely on ventilation.
Long, narrow barn with low ceilings give better tunnel ventilation results. This type of ventilation circulates the wind from an extremity of the building to another. « To refresh the cows, the speed of the air should be increased to a minimum of 325 to 350 feet per minute (1.65 to 1.75 m/sec) », explains Bruno Garon, engineer and head of the agromechanical engineering department at ITA in Saint-Hyacinthe.

A simple calculation allows to estimate the necessary airflow from the ventilators to create the wanted speeds depending of the dimensions inside the building:


Airflow (ft³/min or m³/sec)=speed (ft/m or m/sec)
X height (ft of m) X width (ft or m)
1 ft³/min= 0.000472 m³/sec
In an ideal situation, the air entries are at an extremity of the building and the ventilators at the other. In reality, an extension, a dairy or silos can complicate the makings of tunnel ventilation. That’s why every facility must be evaluated individually.
Choosing the solution
For a conference held as part of INPACQ-dairy cattle day, in the Centre-du-Québec, Bruno Garon evaluated the problems of the Nic at Pic farm. Many factors were shown. First of all, the barn has an L shape. At the junction of two sections, the dairy preclude consideration of an opening lengthwise.
The decision is taken: side windows on the length of the small section near the dairy, that partially open, will be removed and replaced by a 48 by 96 inches long panel that will slide downwards, depending of the needs. At the other extremity of the biggest length, the existing ventilators will remain to lower cost. An additional 72 inches ventilator with variable speeds (65 000 CFM ft³/minute) will be added. The new ventilator and openings are electronically controlled.
Hot is too hot
Armed with fur, cows prefer fresher temperatures. Tell yourself that when you have to put a good sweater under your work clothes, the cows are comfortable. So, when the summer heat comes, they suffer of thermal stress. A hot temperature is to hot for them.
To cause no stress to the cow, the room temperature should be between 5 and 20 degrees, but the effect of humidity should be understood. If the wind lowers the effects of the heat, the humidity increases. When the feeling of heat increases, the respiratory rate of the cow increases. Have you notice cows with their mouths wide open and drooling in the middle of summer?
« We shouldn’t surpass 27-28 degrees with the humidex factor, explains agronomist Gervais Bisson, developer for ruminant affairs for Agribrands Purina Canada.The agronomist analyzed the data from the Lennoxville weather center.
Wind is the first option to cool down a cow. If the solution is not enough, water is left. But beware! Avoid misting! « The importance is to moist the skin », explains Gervais Bisson. Water absorbs body heat and wind, thereafter, liberates this heat in the atmosphere. « It’s like diving in a pool, he says. In Arizona, they use short cycles in which they wet and dry the cows every five minutes. » In freestalls, Gervais Bisson recommends to cool the cows located in the waiting area of the milking room. It’s a critical zone.
Text by Marie-Josée Parent, agronomist for the Bulletin des agriculteurs
Edit: Catherine Ruscigno



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