All Hot and Bothered …

With temperatures soaring recently in to the mid 30’s it fuelled much conversation about ventilation and particularly fans. With a lot of farm opinion seeming to hinge around it being good just to “move the air about a bit” I thought it was a good time to discuss heat stress, before you spend your hard earned and regret it.

This is the temperature and humidity index (THI) that tells us from ongoing research when cows suffer heat stress. It is altering as our understanding of cows continues to grow, for example at 32 °C and 45-95% humidity, moderate to severe heat stress occurs, rising to severe stress the closer it gets to 100% humidity.

This ongoing research has shown that we need to remain below the 68 THI figure, if we do not want to reduce dry matter intake (DMI) and milk yield. This figure allows a calculation to be done on potential milk loss and so we know that a THI of 75 for over 8 hours will result in a 1.1 litre milk drop.

We have regularly measured many of our sheds in the winter at over 20 °C, outside temperature and humidity doesn’t totally dictate the atmosphere in the shed. However, it is the humidity that is the killer. As a country we are prone to high humidity, but think about what happens in the cow shed. Cows produce moisture as they sweat and respire to try to lose heat, they also drink considerably more which adds to the problem, so relative humidity climbs in the shed irrespective of outside humidity. Plus, many housed cows are higher yielding, producing more heat as a result of higher DMI and metabolism rates. Hitting 30 °C in a naturally ventilated shed can be quite easy even if outside temperatures are low to mid 20’s.  Many sheds sit at over 75% humidity you would lead to moderate to severe heat stress on a reasonably regular basis.

So how do we try to solve this issue. A crucial factor is trying to get the cow back to its normal temperature at night. If you can achieve this then controlling heat stress is a lot easier, but if she builds and builds temperature over a number of days then heat stress will be far more severe. Ventilation is king/Queen. You must be able to get hot air out and draw cool air in. Unfortunately, when we smoke bomb many sheds the air doesn’t even get near the ridge to get out as there is insufficient draw. Most of the time we can have some significant effect on this without major cost, just time and effort, but increasingly we need to rely on fans to aid the situation, particularly in high yielding cows.

A fan that that just moves air around and doesn’t actually help to move stale air out and pull clean air in, is simply a waste of time and money. Not only will it fail to cool the cow, but it will do a great job of stirring around any bugs that might be in the shed. If you want to see a human example of this go to the doctors in the winter and sit in the waiting room for a few hours in the heat and see how well you feel a couple of days later!

Cheaper fans can work, but be aware that their longevity is often significantly reduced and make sure that you understand the distance that the fan is able to move air consistently so that you can work out whether the number of fans that you are being quoted for is actually going to work in the area that you need to ventilate.

So, what are the overall effects of not doing anything if you have a problem. Well we already discussed potential loss of milk. But alongside that the butterfat drops due to rumen instability from lower intakes etc and this has a knock-on effect on energy so milk proteins reduce alongside the obvious effect of reduced fertility. Not only does the cow struggle to express heat due to high temperatures, but the embryo is very susceptible to uterine temperature changes and is likely to get thrown out in the early stages. The next affect is on feet as cows stand for longer to expose greater surface area to try and cool down, so then lameness becomes an issue in the future. Meanwhile, immune function is challenged making her more susceptible to disease and mastitis.

Financially we can put some rough figures to it. If we look at many herds across the region they dropped 4 litres for around 3-4 days during and after the hot spell and with a drop in butterfat. At the same time nothing probably held for around a week. So on an average 200 cow herd doing 27 litres taking in to account average milk price and the cost of days open for the cows eligible to breed during that week gives us loss of around £996 from milk litres, £283 from BF and £355 from days open. Total cost not including any semen that might have been used and drugs for sick cows or the cost of trimming lame cows in the future is £1634. That’s from one 3-4 day incident and you could probably add £500-1000 for the other potential risk factors . It makes spending money correctly on ventilation and fans a no brainer.

So if you want to look at fans, take advice from people that understand what they are doing. If they are not looking to check inlet and outlet capability and asking you questions about stocking density and performance levels or aspirations from the shed then they do not know what they are talking about. We are not out and out specialists in this area, but we know enough to make a difference and can help you to quantify whether you are getting good advice or not. Give us a call we’d be happy to help.