The rainfall over the last week has affected ground conditions in the west of Ireland, and despite a record dry summer, these farmers are all too aware that winter housing is just a few short weeks away.

At the same time, weaning is happening earlier on many farms that are finding themselves on the tight end grass wise, with weanling sale numbers now rising rapidly.

Anything that causes stress in an animal’s life leaves them more at risk of picking up diseases as their immune system drops.

Weaning, transport, marts and mixing with other cattle all pose as stressors to cattle, and without proper management, illness and disease can likely occur, with pneumonia being one of the main predators to weanlings.

Pneumonia is a virus spread by air borne pathogens, so keeping cool, fresh air in a shed will greatly reduce the risk of the disease spreading.

Unlike farmers in continental Europe who rely on mainly mechanical ventilation, with extractor fans in place to remove the warm, stale air from sheds, we rely on natural ventilation.

While a much cheaper option, it is not without its faults, mainly where there is inadequate inlet and outlet spacing.

Create an eave outlet

While a lot of sheds have enough air coming in to them, there can often be an issue with an adequate outlet to remove the stale, warm air.

As a rule of thumb, there should be 0.1m3 of unrestricted outlet space for each animal housed while the department specifications relay that a 450mm wide for a house up to 15m wide, 600mm wide gap for a house up to 24m wide and 750mm wide gap for larger houses should be installed.

My preference would be to calculate based on the animals present rather than the size of the shed.

Most eave outlets will be sheltered by a curved sheet raised above the roof.

While this is deemed necessary to prevent the ingress of rain, farmers need to be cautious that this does not impede air flowing out of the shed.

The cover may need to be raised higher than its current position, or be shortened.

Raise existing roof sheets

Raising sheets is a practical method to turn the roof into a “breathing roof”.

One or two lines of sheeting per bay can be raised above the plane of the roof by about 100 mm to 150 mm with an overlap of about 100 mm to 150 mm, at each side, to prevent in-blown rain.

The raised sheets run up along the slope of the roof (which is usually across the width of the shed) and possibly up and over a round roofed shed, as well, if one is present.

A wider, new sheet may have to be used to ensure sufficient overlapping to prevent rain entering. In a five-bay long shed measuring 9m in width with one sheet raised per bay, we will see the air outlet space increased by circa 10m3

Angling of side sheeting

Side sheeting can be angled away from the wall at the bottom to increase the air inlet space along the perimeter walls of the shed. Air is deflected upwards from the side wall as it enters.

This can be done easily enough with box section steel.

Opening doors

Using doors as a supplementary air inlet is usually discouraged as it can lead to draughts, but in extremely mild conditions with little to no wind, they can be useful to allow more clean, fresh air to enter the building. Extreme caution needs to be exercised that draughts are not created.

Knocking blocks

In older sheds, block walls were built up close to the eaves with no side sheeting used.

The top line or two of blocks can be knocked to increase the air inlet from the side. Begin with one line, and if required knock an additional line.

This is a cheap and straightforward fix, with space boarding fitted after should rain entering the shed become a problem.

The stack effect works off the basis that warm air is less dense than cold air, and therefore rises up to the ridge of the roof, bringing with it any pathogens and dust. However, if there is inadequate spacing for an air outlet, then the air will cool and fall down to livestock level again, bringing with it the carried pathogens.

While we often focus on inlet spacing, outlet spacing is just if even not more critical.

A solid way to view airflow in the shed is to use a smoke bomb, available at most plumbing supply merchants.

Lighting the smoke bomb and placing on the floor will allow you to view air movement in the shed, including draughts or trapped air unable to exit the shed. It is best to complete this while livestock are in the shed, but can be done before hand.