Farmers have become more aware in recent times that tackling animal health during the housing period is a multifaceted approach with adequate ventilation just one tool at a farmer’s disposal. We see over the past few months that cattle have had to be prematurely housed on many farms. This means that cattle are going into sheds when conditions can be mild. This can lead to a greater stress on animals which may lead to an increased risk of pneumonia. There can be a lot of pneumonia-causing bacteria and airborne viruses in a shed where air movement is poor. These will remain close to the animals, increasing the risk or animals being affected. Adequate ventilation will dilute and remove airborne contaminants and provide a better environment for cattle. Many farmers will look at older sheds around the farmyard and conclude that bar opening the back door of the shed there is nothing that can be done, this could not be further from the truth.
Farmers have become more aware in recent times that tackling animal health during the housing period is a multifaceted approach with adequate ventilation just one tool at a farmer’s disposal. We see over the past few months that cattle have had to be prematurely housed on many farms. This means that cattle are going into sheds when conditions can be mild. This can lead to a greater stress on animals which may lead to an increased risk of pneumonia.
There can be a lot of pneumonia-causing bacteria and airborne viruses in a shed where air movement is poor. These will remain close to the animals, increasing the risk or animals being affected. Adequate ventilation will dilute and remove airborne contaminants and provide a better environment for cattle. Many farmers will look at older sheds around the farmyard and conclude that bar opening the back door of the shed there is nothing that can be done, this could not be further from the truth.
There is a large variety of sheds in place on Teagasc’s Grange research farm so it made it the perfect site to examine the different ventilation options that are available. The sheds on the farm have been built from the 1970s right up to recent years with many different designs employed. The vast majority of the older sheds have received upgrades over the past 20 years to improve air movement within the sheds.
Does it stack up?
The stack effect is what people will often associate with air flow. This is where hot air rises because it has a lower pressure, this will, in turn, pull fresh air into the shed. However according to JJ Lenehan, buildings officer with Teagasc, this is not the main form of air movement. “With the wind we have in Ireland the stack effect will only really apply for 10% of the year, typically on a calm day. The other 90% of the time it will be the wind that predominantly drives air flow.” For this reason the design of a shed will be heavily influenced by its position in relation to the prevailing wind. When building an open-sided shed, it is strongly recommended to keep the open side facing away from the prevailing wind. This will depend on the position of the shed and if adjoining sheds could provide shelter to the open side.
Some people will often wall the front of a shed, as opposed to leaving it open. For JJ, this is not necessary. “You want as much air movement through the shed as possible without causing any draughts, if you can position the front of the shed away from any prevailing wind then I would leave it open.”
Stale air
“It is not just about getting fresh air into the shed, but it is also about getting the stale air away from animals and out of the shed,” according to JJ. Outlet ventilation must be provided along the full length of the roof apex, depending on the width of the house. Another form of providing outlet ventilation is the use of spaced sheeting in the roofs of sheds as seen in picture 3. JJ is a big advocator of spaced sheeting as it can act as both an inlet and outlet for air. “Some people will be cautious with the amount of moisture that can come through the spaced sheeting but it is very minimal.”
The vast majority of both old and new shed roofs on the farm have been fitted with spaced sheeting. Where spaced sheeting is used, a gap of 20mm between sheets is recommended for beef and sheep units. For dairy cows, a gap of 15-20mm is recommended between sheets, while for a creep area in suckler sheds a 12mm gap is recommended. Where spaced sheeting with a gap of at least 20mm is installed over the entire roof then a central ridge outlet is not mandatory, according to the Department specifications, however is strongly recommended.
The difference in sheds built in the 1970s or 1980s and those built in more modern times is substantial. There is a large difference in the height of the buildings which is partly to compensate for the increasing size of the machinery in use on farms. One advantage of these higher sheds is that they provide a much larger cubic capacity in the shed which helps the dilution effect on contaminants and ensures that the airborne bacteria and viruses are not at animal level, if there is sufficient airflow in the shed. There are many older sheds in place on farms that are still in good condition. The option to improve airflow in these sheds is something which should be explored by farmers and may mean that these sheds stay in operation and are fit for purpose.
Inlet ventilation
The inlet ventilation for sheds can vary depending on the size of the inlets. Ventilation must be provided directly under the eaves for the full length of each side of the shed, or the lower side of a single pitch, open shed. Department of Agriculture, Food and Marine specify inlet ventilation requirements as follows;
Option 1: An unobstructed depth of 450mm must be provided in houses up to 15m wide; 600mm deep in sheds up to 24m wide and 750mm deep for bigger sheds. An overhang of 400mm is recommended when unobstructed inlet ventilation is used, however this will not always work. We see in picture 6 that where the inlet was left facing the prevailing wind too much rain and wind was getting in so it had to be resealed as there was a calf creep located directly adjacent to the inlet. This re-emphasises the fact the ventilation is not always a straightforward solution. The positioning of the shed can have as much effect on the air movement as anything and here the prevailing wind was causing issues. Option 2: To reduce wind-speed and rain, vented sheeting can be used. This is used very prominently on the sheds in Grange, however there can be a big difference in the size of the openings on the sheets which could have an effect on air flow as seen in pictures 4 and 5. In accordance with Department specifications they must be positioned immediately below the eaves and run the full length of the shed and have a minimum depth of 1.5m. For buildings between 15-24m wide there must be an unobstructed opening of at least 300mm above the 1.5m vented sheeting, this increases to 450mm for buildings over 24m wide.
It is also strongly recommended that vented sheeting is also used for the gable ends of sheds including the doors. “There would be very few doors closed on the sheds on the farm,” according to JJ, “but when you have the vented sheeting on the doors you have the option to close them whether it is to keep out birds or for whatever reason.” One of the most recent sheds built on the farm (picture 1 and 2) is used for calving cows, so doors would be kept closed to prevent draughts on the calves. However with vented sheeting used on the entire shed, ventilation is not an issue.
Option 3: Spaced boarding can also be used in the side inlet gap (picture 6). These must be a minimum of 1.5m deep. Laths must be 25mm thick and a maximum width of 75mm with gaps of at least 25mm between laths. While adequate ventilation can be got from spaced boarding, JJ raised concerns about the increased labour requirement when fitting these and the reduced life when compared to vented sheeting. Read more
Watch: unlocking full farm potential with an underpass
TAMS payments continue for farmers
This is a subscriber-only article
SHARING OPTIONS: