Fend off foot-and-mouth by improving ventilation
Fend off foot-and-mouth by improving ventilation
Badly ventilated cow buildings increase
the risk of disease, including air-borne
foot-and-mouth. Jeremy Hunt finds out how
to quickly check and improve ventilation
THE unlikely combination of a wheelbarrow full of straw, a bucket of water and a box of matches could be a lifesaver in beating disease – including foot-and-mouth – in cow housing.
Shropshire-based dairy consultant John Hughes says that positioning a wheelbarrow of dampened straw in the centre of cow housing, setting it alight and allowing it to smoulder will provide a tell-tale picture of the level of ventilation in the building.
The direction and movement flow of smoke from the smouldering straw will provide producers with the cheapest and most effective method of evaluating ventilation, he explains.
"Where the smoke goes will show you where the air goes. In a badly ventilated shed smoke will rise from the barrow, curl and then drift outwards from the centre of the building.
"It will pass over cows, start to rise and then be blown back and re-circulated downwards by the down-draught from the ridge ventilation on the roof. This is exactly what should not happen; eventually air will be blown out through doors or sides."
Over-crowded, ill-ventilated cow buildings are creating a damp, humid environment in which pathogens will thrive.
"Research is showing that this is increasing the risk of TB and heightening mastitis spread. Unless air is circulating correctly through the building a herd is more vulnerable to air-borne foot-and-mouth infection."
Although cowls are common along the ridge of sheds, Mr Hughes explains they do nothing more than take air blown up the roof on the outside and suck it down onto cows inside.
But producers who want to make immediate improvements to poorly ventilated cow housing should not simply remove ridge cowls. "That will only create an even stronger down-draught, so the air inside the building would be driven out through the sides and doors.
"The aim is to bring air into the building from the sides and then take it out through the roof. This correct level of air flow and ventilation will keep cows healthy."
Mr Hughes says badly ventilated buildings are depriving cows of oxygen and affecting their ability to metabolise food. "In a badly ventilated environment cows have to work harder to draw in enough oxygen to metabolise their food. They start to breathe faster. Where cows are seen to be breathing quickly in an effort to lift their respiratory rate its is a sure-sign that there is a ventilation problem.
"The energy cows use to achieve this respiratory boost should be energy they are turning into milk production. Fresh air means good respiration levels, a lower energy requirement and the potential to produce 200 extra litres/cow/lactation.
"A cow gives off the equivalent amount of heat produced by a one bar electric fire. With 150 cows in a building and poor ventilation youve got a very hot building with warm air rising, condensing on the roof and then dripping back on to cows as moisture. Roof purlins with stripes are a tell-tale sign of bad ventilation."
Mr Hughes says many herds are still housed in buildings built using ADAS grants 30 years ago. Cost-saving measures produced buildings with low roof height to the eaves – say 2.4-3m (8-10ft) – and fitted with ridge cowls.
The limited amount of interior space reduced air movement, in addition it was considered that space boarding along the sides offered sufficient ventilation.
"In those days ventilation was never studied as part of cow building design, although pig and poultry housing was well ahead on ventilation with chimneys and ventilators along the roof.
"Traditional cow buildings, built before the ADAS grants, had a 25deg pitch which created a chimney effect. They had tiled roofs that breathed and louvres for ventilation. But as herds got bigger there was a need for wider buildings.
"The roof pitch was lowered to 18deg, roof sheets replaced tiles and louvres were removed and replaced with cowls. Low cost was a priority.
"In ventilation terms, thats about as bad as it gets. It was a time when production was more important than cow welfare."
Emergency measures to improve the ventilation in cow buildings to reduce air-borne spread of foot-and-mouth must aim to achieve a chimney effect.
"Opening up the ridge by taking off the cowl is not enough. Its essential to open the ridge and then fit upswept ventilators 9in apart inside the building to create a chimney and take air up and expel it.
"And you could cut 1ft off the top of the space boarding beneath the eaves along the full length of the building and really get some good air movement." *
• More on ventilation next week.
Checking how smoke disperses in a cow building will quickly show how well it is ventilated.
Improving ventilation may reduce risks of foot-and-mouth entering a dairy herd, says John Hughes.
VENTILATION OBJECTIVES
• Create chimney effect.
• Open up ridges.
• Alter space boarding.