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Archive: Fresh Air is Free

Published 19 June 09

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Fresh air is free and is one of the best antivirus agents there is, according to Jamie Robertson, from Aberdeen University, speaking at a DairyCo on-farm ventilation event in the West Country."When it comes to looking at good building ventilation and reducing calf pneumonia there are three key things to bear in mind, moisture, fresh air and air speed. If you get these right not only will you provide a healthy environment for you cattle, they'll also have a positive effect on mastitis and production," says Mr Robertson.

"There is no doubt pneumonia is more of a problem for us now than it was a couple of generations ago," he explains. "There are now more valid viruses moving around, stock now  moves from farm to sale to farm much more frequently, allowing contamination, and diseases such as BVD and Johne's disease put cattle's immune systems under more pressure. Stocking rates are higher than in the past and above all the modern dairy cow produces much more heat and twice as much moisture as 30 years ago.

"Pressure on our buildings is escalating and in many cases they haven't changed much in the last 100 years! Cases of calf pneumonia have a huge cost to the dairy herd (see box 1) and I'm convinced there is much we can do to prevent it. It's not about large capital investment, although there will be a cost associated with your time, but practical things you can do to your sheds that will make a real difference. Mr Robertson continues; "You want to reduce the amount of moisture in cattle accommodation as bugs thrive on moisture. Think about putting sand under calf bedding to lock moisture into the bedding. Make sure farm yards drain rain water away from calf housing, put in a simple drain if you need to.

"Respitory disease is spread by air particles. In five minutes 99% of respiratory virus particles are dead in clean, fresh air conditions, but in a muggy environment they can last ten times as long. Not only will stale air hugely increase the probability of spreading infection, you can be sure it is the sick animal that is shedding huge amounts of virus that finds the quiet muddy corner to lie down in. "Fresh air is a great antivirus agent and you want to encourage the right amount of it to enter your building. This is where the stack effect comes in," says Mr Robertson. "The stack effect theory was understood over 30 years ago and works on simple principles. "All cattle give off radiant heat and as the air is heated it rises. If there is an exit in the right place it will leave the building. Then negative pressure inside the building will draw clean air into it from the sides. A well ventilated building needs enough space to draw the right amount of fresh air in and follow the same amount of stale hot air out.

"Getting the balance between enough openings in a shed to draw in fresh and push out stale air, and excluding harsh weather means you need to consider options such as covered openings in roofs and space boarding, Yorkshire boarding and perforated sheeting such as Galebreaker." Air speed is also important as drafts cause stress to animals. Whilst dairy cattle can tolerate pretty low temperatures without too much problem the real problems develop when the animals are put in drafty areas. "Drafts will really hammer the calf's immune systems," explains Mr Robertson. "It's not such a problem for loose housed calves as they will endeavour to get out of the draft but if they are penned and can't get away from the weather you will notice that calves in the pens in the draft will suffer."

Henry Shiles and his daughter Joan have been looking closely at ventilation in all the calf and cow accommodation at Barley Close Farm, Codrington, Bristol. DairyCo organised an on-farm event for producers across the country to come and swap ideas and discuss aspects of ventilation with Mr Robertson. "Until my daughter Joan returned from college two years ago and decided to carry on dairy farming I wasn't sure about the direction of the business," explains Mr Shiles. "As a result the buildings have been a bit neglected and, as on many dairy units, calf and cow accommodation has evolved. This means we have calves in buildings that weren't designed for them and stocking rates higher then buildings would have been used to in previous years. "Over the years herd size has increased, we now milk 320 cows, rear all our own replacements and at the moment have extra pressure on stocking rates as we are closed down with TB. We need our buildings to work as well as possible for us," he explains.

Mr Robertson was able to walk round the buildings with the Shiles and a group of producers to look at what worked and what didn't when it came to ventilation and what could be done, with minimal cost, to improve air flow. Calves are housed in a variety of buildings on Barley Close Farm. Mr Shiles and many of the producers at the event noted that it was often just after weaning that calves seemed to be having real a problem with pneumonia. "It's all about managing the stresses placed on your calves," said Mr Robertson. "If calves are becoming sick after weaning usually it is because they have been challenged by the virus before, but it is the added stresses round weaning (change in diet, maybe a change in building or a change in group) that have caused the disease outbreak.

"Whenever you look at the ventilation in calf housing you need to think about the three key areas, moisture, fresh air and air speed. Where there are large open areas (pic 1), and more than adequate in flow for air, think about using a mesh or weather breaker to reduce the amount of moisture that enters the building due to rain. Jamie Robertson warned about the risk of drafts entering the calf housing and putting already challenged calves under more stress; "If the wind hits the steel door of this shed (see pic 2) at 20mph it will be channelled up or down and into the gap at well over that speed. It will really put pressure on the calf's immune system. All you really need to do is put a rubber strip at the bottom of this door and block the draft out. 

In one of the calf sheds, which only had limited opening on one side for air to be drawn in and no ventilation in the roof (pic 3), Jamie Robertson recommended that the Shiles make three simple box chimneys in the roof to allow stale hot air to be drawn out. If the building was going to be used for calf housing for the next five years he recommended the installation of a simple fan and ducting system that would allow the fresh air from the area near the opening to be moved into the more stagnant areas.

"There is no point investing in the £800 or so to buy the fan and the electricity costs unless you are going to put the holes in the roof," Mr Robertson warns. "If you don't, the fan will simply become an effective way of spreading the viruses round the building. You need to address both the air inlet and outlets in any building to get the balance right."

The Shiles explained that whilst they felt their 270-cow cubicle shed was an excellent building it did feel muggy at times particular at the centre. Mr Robertson calculated that the building had nowhere near the air inlet or outlet it would ideally need. He recommended more outlet space was put in the roof by simply taking out one roofing panel in each bay. This lay over the passage way so any extra moisture that came into the building due to rain could be removed with other dirty water.

He then calculated that if the Shiles simply took a saw to the top of the Yorkshire boarding it would let in a huge amount more air. Solutions don't need to be complex," concludes Jamie Robertson. "It can be as simple as taking an angle grinder to Yorkshire boarding or taking off sections of galvanised steel to allow more air inlet into the building, as in picture 5

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