MMN November 2024 – The Benefits of Good Ventilation

 

Many businesses have housed dairy cattle earlier this winter due to extended periods of wet weather, poached fields, limited grazing and variable (but often mild) temperatures. Protecting the herd from the elements shouldn’t be the only consideration when it comes to housing. The airspace within a shed will have a significant impact on animal health and productivity.

 There are three fundamental factors that should be controlled by ventilation within a shed to maintain ideal conditions for livestock:

 

• Fresh air, that is as free from bacteria, dust and the gases produced by cattle as possible. Ammonia levels over 25ppm will aggravate mucous membranes and the respiratory tract, making the animals more vulnerable to respiratory diseases.

 

• Excess moisture can harbour harmful viruses and bacteria, which can increase the risk of infection transmission and increase the prevalence of pneumonia and mastitis.

 

• Draughts should be controlled by ventilation. Excessive air speeds around livestock will increase discomfort and the rate at which body heat is lost in cold weather. While adult cows are more tolerant of colder temperatures and higher than desired windspeeds in sheds, young calves will be more affected. In these colder months calves will use more energy to maintain their body temperature, directing energy away from growth and building their immune system. The lower critical temperature (LCT) is the temperature below which a calf requires extra energy to stay warm. A calf between 0 and 3 weeks of age has a LCT of 10-15°C (dependant on wind speed) and a calf over three weeks old has a LCT of 5-10°C. However, draughts (i.e. air speeds in excess of 0.2m/s) can produce a cooling effect on the calf causing the LCT to increase.

 

To maintain good growth rates in calves throughout the winter months the following could be adopted:

 

• Dry newborn calves to reduce heat loss.
• Use a max/min thermometer at calf height to monitor the shed temperature daily.
• Ensure the shed has good drainage to reduce dampness.
• Use calf jackets if the temperature drops below 15°C.
• Review milk feeding rates to ensure you are feeding sufficiently for your target growth rate.

 

A well-ventilated shed will allow fresh air to be pulled in and stale air to be pushed out whilst avoiding draughts. This movement of air is driven by thermal buoyancy, more commonly known as the ‘stack effect’. The stack effect occurs when the heat generated by cattle warms the air, which causes the air to rise. The warm air that contains bacteria, dust and moisture escapes through the shed outlet. Fresh clean air is then drawn in through side wall inlets.

The stack effect – ventilation by thermal buoyancy

 

If there is insufficient outlet, the warm air will fail to escape the shed, cooling before falling back down onto bedding, increasing the moisture content and providing the ideal environment for bacteria to flourish. At a relative humidity of over 75%, viruses and bacteria are able to survive for sustained periods of time, increasing the spread of disease between animals.

If there is insufficient inlet, there won’t be enough cool, fresh air drawn into the shed. Warm air will rise more slowly, giving it time to cool before reaching the outlet, which allows pathogens and moisture to stay in the shed.

A cow requires 0.1m² of ridgeline outlet and growing cattle and calves require 0.04m² of outlet. The area of required inlet is double that of the outlet (0.2m²/cow and 0.08m²/calf). Very young, small calves will not generate enough body heat for the stack effect to work. Mechanical ventilation such as a fan and tube system would be more practical in a calf house.

An example of good ventilation with adequate inlets on either side of the building and a wide outlet in the ridge

You can test how your sheds’ ventilation stacks up by using a smoke bomb to observe how quickly the smoke escapes from the shed. If the air clears within 60 seconds, this will indicate there is adequate ventilation. If the smoke takes over 60 seconds to leave the shed this would signal that alterations could be made to improve airflow. A well-ventilated shed can help lower your bedding bill and increase productivity of livestock by up to 5%, which makes any investment in shed alteration seem worthwhile. For more information see the Technical Note on Cattle Housing and Ventilation by the Farm Advisory Service:

https://www.fas.scot/downloads/technical-note-tn689-cattle-housing-ventilation/

 keira.sannachan@sac.co.uk; 01555 740497