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DAIRY SPECIAL: Smoke bombs aid understanding of building airflow

Good ventilation is vital for the health and wellbeing of housed livestock and one inexpensive way of measuring air quality and movement in buildings is by using smoke. Hannah Noble reports.

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Sean Hughes, Shropshire Farm Vets
Sean Hughes, Shropshire Farm Vets

The main aim of good ventilation is to promote air movement within a building even on a still day, but without exposing livestock to high winds and draughts in more unsettled weather conditions.

 

Sean Hughes, of Shropshire Farm Vets, says good ventilation is vital from an animal health point of view.

 

He says it is important to remove any stale air which may contain harmful material, not just viruses and bacteria, but also hazardous gases and irritants, such as ammonia and dust, which can lead to diseases and conditions such as pneumonia.

 

Mr Hughes says: “Ventilation is important for removing humidity and moisture from the environment. Fewer pathogens survive in dry conditions rather than in a wet, humid environment.

 

“Pneumonia is one of the biggest issues in older growing cattle and one of the most costly. If there is a high incidence of pneumonia, farmers should be scrutinising all aspects of husbandry and housing. Testing the shed ventilation is also important.”

 

Mr Hughes says the cost of pneumonia is not only the losses at the time and the vet’s bills incurred, but there are implications throughout the animal’s life, due to reduced growth rates and susceptibility to further disease.

 

He says: “Different ages of cattle have different ideal conditions for growing in. Older cattle tend to be more tolerant to temperature and humidity. Younger animals are not as tolerant, as they do not produce so much heat themselves and tend to be more vulnerable.”

 

Smoke bombs can be bought from a plumber’s merchant. They burn for about 30 seconds, producing about 15cu.metres of smoke.

 

Mr Hughes says it is possible to make your own using damp hay or straw, but these can be unpredictable.

 

Once lit it should be placed in a bucket of sand or gravel and placed at animal level. Mr Hughes says placing the bucket on the floor of the shed among the animals is sufficient.

 

The smoke bomb test should be carried out with cattle in the building to provide an accurate result.

 

Record the direction of the smoke’s exit from the building and the time it takes to disperse to give an indication of the frequency of air changes.

 

Refer back to records and repeat the test once adaptations to the building have been made to measure improvements.

Smoke bombs can be bought from a plumber's merchant.
Smoke bombs can be bought from a plumber's merchant.

The test should also be repeated at different times of the year when housing all-year-round in order to gain an understanding of how the building performs in different weather conditions.

 

Be cautious when using smoke bombs in sheds with older animals as they can easily spook at the smoke.

 

Mr Hughes says: “Smoke bombs do not give you any readings as such. They are very crude, but it is a good way of visualising air movement throughout the whole building.

 

“Typically, the plume of smoke will rise and slowly drift off in the direction of the airflow, but if smoke moves in a horizontal direction towards a door or outlet, you know the wind speed there is reasonably high, so it might indicate there is a draught at calf level which is not ideal. Anything more than 0.5 metres/second is considered to be a draught at calf level.”

 

Mr Hughes says in some very poorly ventilated buildings, smoke will hang around for several minutes and seem to disperse within the air, not really leaving the building, or it sometimes collects in one area of a shed. Often he says areas of a single shed can be more prone to disease.

 

He says: “Measuring the length of time taken for smoke to disappear can be useful in calculating air changes. The guidelines state there should be 10 air changes per hour over winter and this is increased to 60 air changes per hour in summer.”

 

A smoke bomb will give you an indication of airflow, but they can be used in conjunction with measurements of air speed and temperature to provide a more comprehensive picture of the environment.

 

Depending on the result of the test, Mr Hughes says there are several changes which can be made to buildings to improve the airflow and overall environment for cattle.

 

“It depends on the age of the animals, but older animals usually produce a good stack effect. If the outlets are not adequate, it is important to address.

 

According to AHDB, the approximate requirement for ridge outlet area is 0.04sq.m per animal up to 100kg, then 0.1sq.m/head for fast growing and adult stock. However, AHDB says these figures need to be modified depending on stocking densities and roof pitch.

 

AHDB recommends inlet areas need to be at least twice the calculated outlet areas, and ideally four times larger.

Ventilation is important for removing humidity and moisture from the environment.
Ventilation is important for removing humidity and moisture from the environment.

Mr Hughes says: “A group of young animals may find it difficult to produce enough heat to create the stack effect in a larger building, so by essentially creating a shed within a shed, they are more likely to produce enough heat to move the air effectively.

 

“You can also install fans or tube ventilation to create positive pressure. It increases airflow in the environment as well as pressure. The air then has to go somewhere, so it is effectively squeezed out of the sides of the building.

 

“However, you need good guidance on how and where to install them, ensuring you are not causing a draught, but sufficient to aid air movement over animals.”

 

If the smoke bomb reveals signs of draught at calf level, Mr Hughes advises creating micro-environments to protect them using bales of straw and other obstacles for them to shelter behind.

 

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