Managing in the heat
Go on alert
Anticipating hot weather
In the hot season, one of the key roles a herd manager must play is that of weather forecaster! If you can roughly predict when an excessive heat load event is likely to occur you can be prepared – forewarned is forearmed.
The trick is to be constantly aware of the weather you have just experienced and what is likely to be coming. A combination of some or all of the following weather conditions increase cows’ heat load and should act as a warning:
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Weather condition
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Effect on heat load
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High daytime temperatures – two or more days
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Back-to-back hot days mean heat load accumulates, gradually rising each day of the heat wave.
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High overnight temperatures
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Limits the amount of heat a cow can off load over night
(This is of greatest concern in high-production herds).
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High relative humidity
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Limits the effectiveness of a cow’s evaporative cooling
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Recent rainfall
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Increases humidity
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Little or no cloud cover
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Increases the amount of solar radiation that a cow is exposed to during the day
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Little or no air movement
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Limits the effectiveness of evaporative cooling
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A sudden change from cool, mild weather to hot conditions
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If this occurs in late spring/early summer cows with no previous exposure to heat are particularly vulnerable
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Relative Humidity
is the ratio of water
vapour or moisture
in the air (at a
given temperature)
compared to the
maximum amount
of moisture the
air could hold. It
is expressed as a
percentage.
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When we consider hot weather and cow comfort we tend to focus on daily maximum and minimum temperatures. These daily highs and lows only tell part of the heat load story. The length or severity of conditions is also important, as is humidity.
Relative humidity is the ‘hidden’ heat load factor and must always be taken into account when assessing cows' heat load. in cows. As relative humidity increases, the cow is less able to cool its body using evaporation – a cow’s primary mechanism for unloading heat.
A simple chart in the back of your paddock book might help you keep track, but get into the habit of using the Bureau of Meterology website and the Cool Cows website to help monitor weather conditions - in the end relying on 'gut feel' may not be good enough to avoid problems.
To keep an eye on weather conditions expected in your region of the coming weeks and their likely effect on your cows’ heat load, use the Weather Forecaster tool.You can also access it via www.dairyaustralia.com.au.
