CAFRE beef and sheep adviser, Gareth Beacom, explains why he believes ventilation is the key to healthy animals and profits.
With an average cost of £82/head per non-fatal case of pneumonia in calves, a well-ventilated building is one of the most essential assets on any suckler farm this time of the year.
This is not only to maintain and improve animal health and welfare but also to enhance animal productivity.
Here are some key points to consider when assessing ventilation in new or existing buildings.
A building to be well ventilated needs two key things: sufficient inlet and sufficient outlet.
Outlet ventilation
The amount of outlet needed will vary depending on the stocking density of the house and the distance between the inlet and outlet.
This can be tricky to measure exactly but can be estimated by reference points in the gable end, e.g., rows of blocks or sheets of tin.
It then can be calculated for your specific shed and the type of cattle in it.
A general rule of thumb based on recommended stocking densities and a distance of 2 metres between the outlet and inlet is that animals over 500kg require 0.1m2 per animal (and 0.04m2 for young calves).
For example, a 5-bay shed approximately 23 metres long with a ridge gap of 8 inches (20cm) will have an outlet of 4.6m2.
This would be enough of an outlet for 46 cattle over 500kg or 32 cows and calves.
Ideally, the open ridge would be left open to restrict any airflow.
However, if it needs to be covered to prevent rain from coming in, then the cover’s height should be 50% of the width of the ridge.
For example, if the ridge is 30cm in width, the cover should be at least 15cm clear from the roof.
Angled uprights from the ridge gap are another alternative to the cover. These are a much better alternative in terms of ventilation than a cover and will keep out the majority of the rain.
If an open ridge is not an option, then spaced sheeting also should provide enough of an outlet if spaced an adequate amount throughout the house.
Inlet ventilation
Once you have calculated the outlet, you can calculate the inlet. The inlet area should be at least twice and preferably four times the outlet area (0.2 – 0.4m2 per animal over 500kg).
The inlet to the building needs to be above the head height of the cows to avoid a draft on them.
It is normally supplied by either spaced boarding or Yorkshire boarding along the length of the building.
Inlets along the sides of the building are usually sufficient unless your shed is excessively wide (over 25m in width), in which case inlets along the gable ends will be needed also.
Compared to spaced boarding and Yorkshire boarding, vented sheeting offers considerably less airflow and hence inlet for the building.
Spaced boarding is generally achieved by a 4inch board with a 1inch gap in between, as you can see in figure 1.
Yorkshire boarding is usually constructed using 6-inch boards with a 2-inch gap in between (figure 2) hence allowing more air to enter via the larger spaces and with the overlapping rows creating a barrier to the weather.
If designing a new shed, the positioning of the shed is critical. The shed should be positioned to catch the prevailing wind through these inlets to maximise airflow through the building.
Hence positioning the building at a right angle to the prevailing wind and away from other buildings and high trees etc., will maximise airflow.
However, if it is an open-sided building, the open side should be positioned wherever it gets the most protection from the prevailing wind.
Troubleshooting
If there is a ventilation problem in an existing shed, then some modifications may be possible to alleviate the problem.
The inlet can be increased by replacing spaced boarding or side sheets with Yorkshire boarding.
Windbreakers also offer a solution to some buildings to allow a controlled airflow but prevent rain from getting in.
Alternatively, the bottom of the side cladding or side sheets can be angled out from the wall at the bottom to allow for a clear gap between the wall and the side sheets.
Air is then angled up from the sidewall as it enters.
The outlet is more difficult to modify; however, some lines of sheets in the roof (one or 2 per bay) can be raised to allow for an increased outlet.
These can be replaced with wider sheets to allow for an overlap and prevent rain from getting in.
Alternatively, if there is a ridge cap on the roof, this could be raised if possible or the gap widened.
Ventilation systems
Mechanical ventilation systems are also becoming increasingly common on farms.
There are two main types:
- Ventilation fans;
- Extractor fans.
Ventilation fans draw in fresh air from outside; hence a good outlet is essential.
These are particularly useful in stuffy conditions when airflow is poor or when the siting of a shed doesn’t allow for much natural ventilation.
On the other hand, Extractor fans assist with extracting stale or moist air from the ceiling areas of sheds with poor outlets.
These work better in smaller confined areas; however, various sizes of extractor fans are available.
Whilst there is a cost in all of the above, the payback in terms of:
- Increased daily live weight gain;
- Reduced dependence on medication;
- In severe cases, reduced mortality.
They will make it a worthwhile investment, particularly when you consider the lifespan of most farm buildings.
Fresh air is a natural disinfectant and can remove viruses, harmful bacteria, and dust from the shed; hence, the more we can get moving through sheds, the better.
No matter what type of shed you have or are designing, the target is always the same.
That is to maximise airflow and ventilation on a still day without exposing the animals to a draft on a windy day.
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