Ventilation - follow the herd
Good ventilation in livestock buildings is a critical factor when looking to maximise animal welfare and following a few simple design rules can make a dramatic difference. Here, Jamie Robertson, research fellow at Aberdeen University, who has partnered with Marley Eternit, looks at some simple steps that farmers can take.
“Getting fresh air to livestock is free and is one of the best bactericides and virucides we know. Yet many new livestock buildings have inadequate levels of ventilation and are therefore not fit for purpose. This contributes to sickness and poor health in livestock, which ultimately means they under perform as a business asset. The consequences of inadequate ventilation are therefore far reaching, yet it can be relatively straightforward to remedy if it is clearly specified at the design stage.
Farm buildings are one of the single largest investments that farmers make, which is why it is so important to get the design right from the start. Choosing the size, layout and location are all fairly easy decisions as farmers know exactly what suits their existing operations. However, the ventilation requirements are often not designed for the number and type of cattle kept in the building.
Considering that a single cow generates around 10 litres of moisture through respiration every day, and there may be up to 100 cows in each unit, dispersing this effectively is essential. To put this into perspective, 100 cows generate one tonne of respiratory moisture each day! Where there is a lack of ventilation this moisture as well as from other sources such as urine and spillages from drinking troughs can increase the incidence and severity of mastitis, foot problems, pneumonia and other breathing related conditions.
It was against this background that we set about working in conjunction with Marley Eternit to highlight the following issues:
• Inadequate ventilation causes poor health in the livestock, requiring expensive
antibiotics and reducing performance.
• The ventilation requirements can be calculated for the design of the building and the
expected stock levels at a modest cost.
• Existing ventilation products and systems for fibre cement roofs provide solutions for
all types of buildings.
As a rough guide, adult cattle in a typical building need at least a 200mm gap along the full length of the ridge and here it is important to pay attention to the detail because a few millimetres too little can make a huge difference to the air flow. A ridge opening should be designed to prevent rain falling onto bedding, which would add to the moisture already being generated inside the building.
Air intake area is important too, and should be at least double that of the outlet, and evenly spread around the building to prevent corners of stale air. An adequate intake will ensure circulation of air through the ridge, preventing most rainfall entering the building where an open ridge is used.
To prevent draughts at body level that cause physiological stress, especially in younger stock the advice is to design the building with a solid wall at least to the animals' height. When it comes to cladding the building above this level it is acceptable to use Yorkshire boarding as long as 10-12% of the area is voided.
The advantage of partnering with Marley Eternit was that the company was able to use our research findings to propose practical and cost effective methods of designing adequate ventilation systems in new buildings.”
Here Andrew Brown, Technical Services Manager - Profiled Sheeting, looks at the ways in which farmers can ensure their new livestock buildings are adequately ventilated and avoid many of the issues highlighted earlier.
“In terms of using fibre cement Profiled Sheeting there are four types of roof ventilation that are acceptable, as follows:
a) Open ridges – These can be designed as both an unprotected and protected open ridge ventilation system. They are effective in providing an efficient outflow of air, whilst allowing rain to be channelled away over the roof. The upstand of the open ridge flashings creates a venturi effect to suck air out of the building as wind passes over the roof.
b) Spaced roof
On some of the larger cattle buildings the open ridge vents cannot provide sufficient ventilation, but additional ventilation can be provided by the spaced roofing system. Profile 6 sheets are trimmed so that they finish with an upturn on each side and are laid with a clear gap of 15 – 25mm between each vertical run of sheets. The width of the gap is important to minimise the risk of snow bridging and water ingress.
c) Breathing roof
The breathing roof is another acceptable method of ventilating through a profiled sheeting roof surface whereby timber battens are inserted into the end laps of the sheets to allow ventilation through the corrugation voids. This system requires single spanning sheets to be used (typically 1525 or 1675mm lengths) and allowance must be made for the reduced pitch of the sheets due to the insertion of the battens.
d) Ventilated ridge pieces that can be incorporated in a run of closed ridges are suitable for general storage buildings where occasional access of livestock may be required.
As well as incorporating these ventilation systems into the roof design, fibre cement profiled sheeting has an additional advantage over other materials such as steel sheets in that it is vapour permeable. This reduces condensation by allowing moisture to escape to the outside, which in turn can help to prevent the conditions found in livestock as well as protecting farm machinery.
Semi-compressed fibre cement profiled sheeting can also absorb up to 25 percent of its dry weight in moisture and then dissipate it in more favourable conditions. Instead of the condensation remaining on the underside of the sheets and dripping off at the purlins onto the livestock and bedding, the moisture can be absorbed by the material. Independent testing has shown that in a typical cattle building in southern England, there will be dripping condensation from semi-compressed fibre cement sheets for only 1% of the time during the winter months, compared to almost 20% of the time for single skin steel.
Fibre cement profiled sheeting has good thermal properties too, compared with other sheet roofing products. This helps to reduce heat build-up in summer and heat loss in winter and also contributes to minimising condensation. Also important in buildings that house animals, fibre cement profiled sheets, have a P60 (external SAA) rating to BS 476: Part 3: 1975, and can be classified Class 0 in accordance with the Building Regulations.
Fibre cement profiled sheeting is low maintenance and has a resistance to chemicals, with a life expectancy of at least 50 years; saving money for farmers in the long run. This is due to the fact that it has no metallic content, which is an advantage when used on livestock buildings, where the heat and moisture produced by animals creates a slightly acidic atmosphere.
Jamie Robertson concludes by saying “Adequate ventilation can have a considerable beneficial effect on animal welfare and therefore likely returns from the herd. It may seem obvious but any new building should be designed according to the number and type of animals to be housed. All too often we see examples of where this hasn’t been done, which results in unnecessary and expensive health and welfare issues within the herd.”
"Adequate ventilation can have a considerable beneficial effect on animal welfare and therefore likely returns from the herd. It may seem obvious but any new building should be designed according to the number and type of animals to be housed. All too often we see examples of where this hasn’t been done, which results in unnecessary and expensive health and welfare issues within the herd.”
Research Fellow, Aberdeen University