Housing and Environmental Control Featured Articles
Do pigs really suffer from 'drafts'?
By Nick Bird for FarmEx - So, what about "draughts"? After years of research, I feel I can tell you a little about them. Draughts are something your granny feels, but you don't. They are something that pigs that tail-bite feel, but pigs that are happy do not. They're something that you can't see, touch, feel or smell.
They are something that causes all kinds of problems, such as ill health, poor pig growth, and bad behaviour. But they are something you can't measure or predict.
They are something whose existence you can only imply by the symptoms they produce - such as your granny telling you to shut the door because you're causing a draught, or pigs having bad behaviour or growing badly.
Do I sound sceptical? Well, I am, just a bit. I'm not saying there is no such thing as "draughts" - by which I think we mean sudden and rapidly moving cold currents of air in a room".
But I am saying that they are rather too convenient an explanation for problems. They are so often used in the context of "We can't see anything particularly wrong, and yet the pigs seem uncomfortable, so we think it must be draughts".
The basic scientific principle is okay - air takes more heat from the skin when it's moving quickly than when it's moving slowly. Quickly moving warm air is, effectively "colder". But is that the actual problem?
It's tempting to think that a "draught" is making it seem colder when the problem may be far simpler - the pigs are actually cold! Though possibly not when you are looking.
This chart shows temperatures in a weaner room over about three days in February 2005. During the day temperatures aren't all that bad. They reach the low twenties - a little below Set Temperature, but then it is winter. If you looked at the temperature, you wouldn't necessarily think anything was wrong. But, of course, you don't necessarily look at the temperature reading. It may actually feel quite warm if you've just come in from 5ēC outside.
However, you can see how it dips down at night, and gets as low as 15ēC. This, undoubtedly is undesirably low for a young pig that is intended to be at around 25ēC. Unless you know the temperature at night, you have no particular way of knowing whether they are.
The explanation for the dips in temperature are - in general terms at least - all too clear. The following shows the same data, but presented in a different way.
This shows the temperature lift that would be needed to achieve Set Temperature (I.e. Set Temp minus Outside Temperature) in grey as compared to the temperature lift actually achieved (i.e. Actual Room Temperature minus Outside Temperature).
As you can see, the actual temperature lift is moderately constant at around 16 to 20ēC.
That is - with the amount of pig heat and supplementary heat available, given the rate of heat loss through the structure and ventilation, it can make it 16 to 20ēC higher than ambient.
When that's enough to reach target (Set) temperature, then it reach will target temperature. When it's not, it doesn't, simple as that. Except that when it doesn't - at night - there is least likely there will be anybody to see it. Except the pigs, of course, who are stuck with it.
The most likely causes are not enough pig heat due to insufficient stocking, insufficient heating capacity, or excessive minimum ventilation rate.
But note that, with a temperature lift of 16 to 20ēC, it would achieve target temperature for slightly more than half the time on annual basis. But statistically, low temperatures tend to occur outside working hours (i.e. in the evening and night). It would be able to achieve target temperature during working hours most of the time, even in winter. The chances of seeing the low temperatures by direct observation are low, for much of the year.
In my experience, pig keepers, consultants and veterinarians seem all too eager to ascribe perceived problems to "draughts" - sometimes describing in great details how currents of air bounce off this or that wall or roof truss at certain times. Though there's no particular trace of this or that draught just now, actually. But they're convinced it happens
.Sometimes.
A similar, and in some ways related, issue is the controller. "The controller reacts too quickly, or too slowly, or in the wrong way, or at the wrong time, or
." All or any of these may be thought to create the draughts, though in what exact way is as elusive as the draughts themselves.
For whatever reason, these rather obscure explanations for pig problems seem preferable to the rather more mundane issue of temperature as such. The notion that pigs may actually spend some - or even a substantial part - of their time colder than they want to be, is usually far too readily rejected.
Nine times out of ten, if you ask someone what temperature the pigs are kept at, they tell you what the controller is set to, which is not unconnected, but hardly the same thing. Temperature recording on a large number of pig farms shows that the temperature that pigs are actually kept at, and the temperatures they are assumed to be kept at, are often two distinctly separate things.
Another widespread problem - discussed in earlier articles - is whether or not the pigs are fed. Extensive feed recording shows that, in practice, failure to feed is a lot more common than generally known. If pig feed intake falls, it's heat output falls likewise. Not only is room temperature more likely to drop, but the pig's sensitivity to temperature increases.
In summary, before suspecting "draughts" check the actual temperatures. The easiest way is using Barn Report (or something similar). (The partial screen captures above are from Barn Report, which lets you see at a glance.)
Failing that, max-min readings on controllers can be useful, and if all else fails, use good old max-min thermometers. If using max-mins, compare the inside minimum with the outside minimum to check your worst case temperature lift.
Until you are sure that you can maintain temperatures well, and that you are feeding pigs at each and every meal, don't go looking for contrived and complicated explanations for poor performance.
If Occam were here today - he'd be a bit smelly since he died of the Black Death in 1349 - he would tell us Pluralitas non est ponenda sine neccesitate. Or to put it another way - "Don't invent something that is unnecessary to explain the phenomenon". If the pigs seem cold, it's probably because they are cold. Don't invent draughts until you're sure that they are not.
Source: FarmEx - March 2005
