Dairy cows need to maintain a constant body temperature of 38.8 º C (+/ - 0.5 º C ) and are sensitive to air temperature , radiant temperature , air velocity and relative humidity .

Richard explains : " When a cow becomes heat stressed her feed intake declines dramatically and effects milk yield . Fertility also suffers and studies have shown heat stress can increase embryonic losses . Often cases of clinical mastitis increase as well .

Richard continues : " As humidity increases animals become heat stressed more quickly , which is why cows become heat stressed during the housing period . It is crucial appropriate ventilation is in

place to reduce the risk of heat stress and its associated production and health problems ."

Farmers may be aware of ventilation issues in some buildings after last year ' s warm , wet winter , suggests Richard . " But to test ventilation and humidity cattle need to be living in buildings as their dynamics change once cattle are inside ."

Your extension officer can tell you about a calculation that will work out if a building has ventilation problems , based on its dimensions and cattle numbers .

" Natural ventilation is the least troublesome , most efficient and least expensive system to provide the best environment within buildings ," continues Richard . " You ' re aiming to provide a continuous stream of fresh air to every animal at all times of the day and night . But perhaps even more important is adequate provision for hot , stale air to leave : as this air exits it allows fresh air to be drawn in .

" Hot air rises and builds up in the apex of the roof where it grows stale and condenses . The

water then drips down onto bedding , increasing moisture content and creating a suitable environment for bacteria to flourish ."

Richard continues : " There are a few basic rules when looking at humidity and outlets for this air . The flatter the roof , the harder it is to ventilate . It ' s often odd-shaped buildings , lean-tos or buildings , whose use has been changed to housing , where problems are found .

" Often the solution to poor ventilation is cheap and there ' s no need to invest in fans that can end up blowing stale air around the building . If you follow the correct safety procedures , creating more outlets for stale air to leave is a cheap and effective way to improve ventilation .

" As a useful rule of thumb there should be 5cm of ridge opening for every 3m of building width ."

But Richard adds : " Fans can have a place in the ventilation of large , multi-span or unusual shaped buildings .

" It ' s also important to ensure there ' s adequate inlet ventilation .

As a guide the inlet should be twice the area of the outlet . It ' s a capital expense , but to allow the amount of air admitted through the inlets to be varied according to weather conditions , consider installing curtains to the sides of cubicle buildings ." Food and water

" On average cows drink about 61 litres of water a day but high yielding cows may require more ," says Richard . " Demand for water peaks with the completion of milking and around sunset when up to 50 % of cows ' daily requirements can be consumed . " You need to ensure there is adequate trough capacity , bearing in mind the flow rate of your water supply . And you need to provide adequate trough space to allow 10 % of the herd to drink at any one time . A single animal drinking will require about 700mm of trough space . The surface area of the trough should be 1m ² for every 60 cows in the group .