With the housing period fast approaching on many farms throughout the country, if you have not already addressed ventilation issues in your shed, now is the time to do so. The aim with adequate ventilation is to remove stale air from the shed quickly. This in turn will take away moisture and bacteria from animal level which will reduce disease pressure on them.

One group that will be particularly vulnerable to disease once they come on your farm is purchased weanlings. These are one group that can be highly stressed after weaning and transport and the best option for this group is to allow them to settle on a well-bedded straw court overnight, and if possible keep them housed for the first 48 hours that they are on the farm.

Ensure the shed is bright and airy but prevent draughts at animal level. This group can be particularly at risk of pneumonia so ensuring a good movement of air in a shed, along with other management practices such as vaccination, can go a long way to help prevent pneumonia in this group.

Ventilation options

The Scottish Government have a technical note for farmers, examining in depth cattle housing and ventilation requirements which should be used to help reduce disease pressure in your shed this winter.

The ventilation requirements will differ from farm to farm. For example where a suckler farmer may only house cattle for the winter months, a dairy farmer operating a confinement system will be required to keep cows cool with temperatures sometimes hitting 25°C as was seen this year.

Ventilation should be designed to work effectively on a calm day when there is no wind and as a rough rule of thumb the inlet area should be twice the outlet area and should be split between the two sides of the building.

While this is manageable to install on a new shed when it comes to altering an existing building then it may not be possible and mechanical ventilation may need to be examined as one potential solution.

Changing weather

We have seen the autumn period become milder over the past few years and putting cattle into sheds, when the weather is mild can lead to greater stress on the animals.

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 of animals being affected. Adequate ventilation will dilute and remove airborne contaminants and provide a better environment for cattle.

Due to the weather conditions present, air flow in sheds will predominantly be influenced by wind and for this reason the design of the shed will be dictated by the direction of 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.

When it comes to looking at older sheds, one of the key concerns can often be the low roof that was built. One advantage of 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.

One option may be to remove sheeting from the side of the shed and replace it with either spaced boarding or Yorkshire boarding.

Inlet ventilation options

When it comes to spaced boarding it is recommended that from the eaves down there must be at least 1.5m of spaced boarding. Ideally laths should be 25mm thick and a maximum width of 75mm with gaps of at least 25mm between laths.

While vented sheeting may have a longer life there is a better movement of air through spaced boarding.

According to FAS, if wind is blowing against a building it will create pressure on the exposed side and also suction on the other side. This can lead to a situation where draughts can occur as the wind passes through the building by the shortest possible route. Apart from the options outlined above, Yorkshire boarding or fabric mesh could also be used.

On the continent, retractable fabric mesh is often used along the side of buildings, generally where livestock are housed all year round and extra ventilation is needed during periods of high temperatures.

It allows for a greater control of the air movement within the building and allows you to respond to changing weather conditions.

Yorkshire boarding is the other option that would be used where the site is particularly exposed. Yorkshire boarding, as outlined by FAS, consists of two rows of boards. The row on the outside will normally be 150mm boards, which can be spaced with a 50mm gap, and a new second row on the inside of the purloins with the same gap offset so that the board on the inner row blinds the gap on the outer row. This type of cladding will allow for the controlled movement of air.

Outlet ventilation

When it comes to outlet ventilation, the most common method is by way of a continuous opening along the apex of the shed, with either upstands or a ridge cap in place to prevent rain getting into the shed.

Another option for farmers which can be used separately or in conjunction with an opening along the apex of the roof, is spaced sheeting. This has the added benefit of providing both an inlet and outlet for air. The moisture that will get in between these sheets is minimal and will not affect livestock or bedding. However, outlet ventilation will not work efficiently if you do not have enough air coming into the shed to push the stale air out as seen in Figure 1.

When calculating the required outlet size required in your existing shed, a rough calculation is that for an older building 0.1m2 of outlet ventilation is needed per head, as per FAS. Therefore the stocking rate of a shed will have a large impact on the ventilation requirements.

Straw-bedded courts will generally not be as highly stocked as slatted courts which will hopefully reduce the disease pressure that is placed on animals.

Mechanical ventilation

Another option for existing buildings where ventilation is poor is to install mechanical ventilation. While this is not the preferred solution it could provide a good option where alterations to the shed would prove costly, or may not be possible due to the location of the shed. Fans can be used to push air along a duct and distributed within the building.

However, outlet ventilation must still be provided to ensure stale air can be displaced by fresh air. If not, the stale air will just be moved around the shed, transporting potentially harmful bacteria in the process.

Such a system could be especially useful where calves are housed as they will struggle to produce enough heat to produce the stack effect, where hot air rises up and out of the shed, carrying with it moisture and bacteria. Extractor fans may also be an option where outlet ventilation cannot be altered.

The use of smoke bombs within a shed is a useful way to see how air is moving and this may be particularly important when it comes to examining existing sheds that are in place on the farm. Ideally these tests should be carried out on a calm day when the shed is occupied to give a true reflection of how the air will move when the shed is fully occupied.

You want the air to move upwards and away from the animals and move out of the shed. If it is moving quickly along the floor of the shed it may indicate draughts in the shed.