PLASTICHOUSINGCANSOLVECOSTDILEMMA
PLASTICHOUSINGCANSOLVECOSTDILEMMA
The high cost of housing
often restricts plans for
herd expansion, but there
is one low cost alternative
that has proven its worth.
Carol McLaren reports
MAJOR progress in the design of plastic-sheeted structures could herald the dawn of a new era of flexible, low-cost dairy housing, according to an agricultural building designer.
Mike Kelly, formerly head of SAC Building Design Services and now an independent livestock housing consultant, says cows can be kept in plastic housing. It provides a good environment for animals and stockmen at a lower cost than conventional buildings.
The technology is proving popular with producers overseas, but so far its uptake in the UK livestock sector has been largely limited to basic polytunnel structures for sheep, calves and pigs.
Early structural failures of polytunnels in exposed sites caused some loss of faith in the concept, he explains. However, recent years have seen big strides forward in plastic structures designed for the horticultural sector. Improvements include better structural strength using trellis girders and heavy gauge uprights to rack units together.
The signs are that a breakthrough into wider agricultural application is imminent, especially large livestock premises for dairy cows and beef cattle.
"Plastic sheeting is a developing technology and the future development of an ultimate breathing roof could be a real breakthrough."
He believes modern fabrics, such as Gortex, which are now popular in outdoor clothing because they are waterproof yet allow air in and out, will have a vital role.
Roof advantages
"With a Gortex-style roof the stale air and vapours would be transmitted out of the building, but the roof wouldnt let moisture in. This could offer advantages in reducing respiratory problems – animals would effectively be outside while inside, with high light levels and breathable fresh air.
"The high light transmission of plastic at 60% is also beneficial to stock management and there are indications it may improve stock performance and well-being. Research has shown that when you lengthen the day using artificial light cow performance increases. High natural light levels must induce a better feel-good factor," adds Dr Kelly.
An MDC-funded research project by Dr Kelly suggests that it is possible to build a four-row dairy unit under plastic.
Cost savings for this type of unit are up to 23% compared with a conventional design and 10% on timber kennel structures.
Plastic sheet replacement is inexpensive at about £3/sq m (30p/sq ft). He calculates the cost of re-roofing a 200 cow plastic unit, after 10 years, at £2000-£3000.
The roofs are designed for snow loading and wind problems can be overcome by sensible siting and the correct choice of sheeting. Plastic structures used by the horticultural sector are based on extensive wind-loading research carried out by the Silsoe Research Institute, Beds.
"These structures are being used successfully for permanent garden centres all over the country. The technology is there its just not been transferred to agri-businesses.
"I am confident enough to say it is a way forward. But it is not suitable for all situations, such as housing of cattle in hot summers," says Dr Kelly.
Heat stress in summer months can be minimised with curtain sides which can be fully opened or by adding internal shade screening to the roof.
Dark green – which cuts down translucence by 40-50% – is likely to be the preferred colour. But planning authority stance is uncertain and appearance, siting and colour choice must be carefully considered.
Dr Kelly also predicts that, with increasing pollution regulations, plastic sheeting could also have a role as a covering for middens and silage clamps to reduce run-off risks.
Overseas action
Dairy producers overseas are already embracing the technology for cow housing, as well as equestrian buildings and general-purpose farm storage. The buildings are not particularly attractive to look at, but they are popular with producers who appreciate their high light levels, generous volume and speed of delivery and erection.
Large dairy units in New York State, US, are now housing calves under plastic and an average size 21.6m (72ft) span building can be fully installed within one week.
Dutch company Rovero, a world leader in innovative horticultural buildings, is increasingly focusing on livestock housing. In 1996 it built a 1000-head goat house in Slijk-Ewijk, Holland which has impressive high natural light levels and good cross ventilation.
After four years the roof sheeting remains sound with no signs of wear or ripping, stock performance is excellent and the 4.5m (15ft) clear height allows for large machinery access.
More recently, Rovero has built a dairy cow unit in Holland using the same principles and curtain walling to reduce costs.
Good bio-security
Plastic sheeting could also have bio-security benefits in the case of disease threat. "There have been huge costs to dairy producers in trying to clear up holdings after being hit by foot-and-mouth. You could be looking at paying out £100s to replace plastic sheeting rather than £1000s to disinfect and fumigate cement fibre sheds," adds Dr Kelly.
He believes progress towards evaluating the potential of plastic cow housing in the UK needs entrepreneurial producers and building suppliers to co-operate.
"Such a project would move the debate forward and we would learn a lot about cow performance in a brighter environment than is the norm in UK dairy units," he says. *
The use of polytunnels need not be restricted to calves and sheep in the UK. Improvements in design make them suitable for cows, says Mike Kelly.
• Suitable for cows.
• Low-cost option.
• Durable designs available.