Roof ventilation is key to lower respiratory disease

Housed stock face the greatest challenge from respiratory disease. Hot, humid conditions allow pathogens to multiply and spread quickly among stock, putting younger animals at greatest risk, warn advisers.

But the risks of respiratory disease, in particular pneumonia, could easily be avoided, according to specialists speaking at the recent EBLEX Better Returns West Midlands’ Calf Housing open day at Graham and Richard Clark’s Corner Farm, Shrewsbury. “If you take nothing else away from today, remember that outlet size is the most important consideration for good ventilation,” independent building expert Mike Kelly told delegates.

“The golden rule is the inlet area should be four times the size of the outlet area. For 100 calves, there should be 6sq m of outlet for 100 cows or mature cattle, it should be 10sq m.

“If you don’t have adequate inlet area, you can’t get rid of stale air and moisture generated by stock. Often many producers make the mistake of believing an open-sided building will suffice. In both mono-pitch and pitched roofed buildings, it is outlet in the ridge or roof space that matters most.”

Dr Kelly continued: “If you imagine an open ridge of at least 300mm (12in) along the entire length of a building, then you won’t be far wrong. Those who have crown crank ridges where every fourth tile has a vent, the outlet area is a quarter of that achieved by an open ridge as a guide.”

Matters could easily be rectified, said Dr Kelly. “There are two secret weapons in the ventilation tool chest – a big hammer and smoke pellets. Quite literally knocking out ridge tiles is the single most effective action to improve ventilation in most buildings. Producers worry about rain coming in, but, given the heat generated by livestock, the updraft will prevent most, except in severe storms.

“When necessary, consider fitting up-stands – 90° edging panels – turned upside down and set back about 4in from the edge of the open ridge to minimise risks of rain entering.”

Avoid ground level inlets unless livestock can get away from draughts, he said. Rear walls in open-fronted sheds are ideal spaces. When calves are housed and draughts likely, place boards or straw bales over pens immediately below the inlets to form shelters.

“Checks on ventilation are much easier than imagined,” said Dr Kelly. “Smoke pellets are commonly available from plumbers’ merchants and cost little. When possible, use them when stock are housed and preferably on a still morning when ventilation challenges are highest.”

The plume generated by the smoke bomb should dissipate in about two minutes. “Watch where and how it moves towards outlets,” he added. “Ideally, it should rise to the ridge and escape. Hanging smoke should sound alarm bells – risk of respiratory disease could be high.”

Enclosed corners are areas to watch for stale air. “Even in buildings clad with space boarding, air movement can be poor. Be brave and open up inlets and outlets.”

The old calf house at the Clarks’ Corner Farm had some ridge ventilation, although it could be widened, he said. Smoke tests confirmed the open-sided brick building would benefit from having inlets knocked into the back wall. “It’s asking a lot of fresh air to travel right to the back of the shed.”

Other improvements would be ensuring drainage channels from bedded areas run outside the front of the building. “That will reduce moisture within the housed area and prevent pathogens being passed through one pen to another in dirty water,” he said.

Mono-pitched roofs can be improved by lifting the lower edge of roof sheets by inserting a baton. Roof fans were also considered, but costs can be high. “They cost you twice – first to buy and then to run,” said Dr Kelly. “One client spent £600 a year running two fans when an open ridge would have done it for free.”