As temperatures increase with the summer weather, it is important to think about heat stress in your cattle and what you can do to reduce the impact. Heat stress occurs when the cow accumulates heat due to the higher air temperature, humidity levels and exposure to solar radiation.
The ideal air temperature for a cow is between 5 and 25˚C, depending on breed and weight of the animal. If cows are exposed to air temperatures above 25˚C and a relative humidity above 60%, then the cow can experience heat stress which will trigger behaviours to cool down including increased blood flow, panting and drooling (see table below). Cows may become lethargic with reduced activity; feed intakes may drop and some may stand with their heads bowed.
Lactating cows are more sensitive to heat stress than non-lactating cows. As feed intake reduces, the availability of nutrients for milk synthesis will decrease and therefore, there will be a drop in milk yield. High yielding dairy cows are more challenged by heat stress than lower yielding cows due to the relationship of milk yield and heat production. There is a time lag of between 24 to 48 hours for the milk yield to drop following a period of elevated air temperatures. Bulling behaviour can become more difficult to detect due to the reduced movement or lack of activity by the cows. Heat stress can have an impact on early developing embryos with there being an increased risk of embryo death within the first three days of fertilisation.
Combating heat stress can be done through some simple measures, including encouraging cows to maintain high feed intakes, drinking adequate amounts of water and plenty of ventilation or shade. Feeding most of the diet between 8pm and 8am can encourage feeding as it is during the coolest section of the day. Increasing the energy content of the diet will help avoid the effect that reduced intakes can have on milk yield and quality. Ensuring refusals are cleared regularly to reduce heating of the feed can help maintain feed intakes.
Providing clean, fresh water is essential for keeping cows hydrated during periods of high air temperature. Typically, a cow requires between 3 to 5 litres of water for every litre of milk she is producing and when the air temperature increases, her water intake will also increase. Not only does the water aid in keeping the cow hydrated, it will also aid feed utilisation and reduce the risk of acidosis. Water troughs should be checked and cleaned out regularly to encourage cows to drink frequently throughout the day.
If cows are housed during the summer, then good ventilation is key to combatting heat stress, as this will keep a flow of fresh air coming into the shed and allows for removal of the stale air. A continuous flow of air will help keep the inside of the shed cooler than the outside air temperature. If cows are grazing during the summer, consider bringing them indoors during the hottest part of the day. In the paddocks, ensure that there are plenty of water troughs which do not require a long walk to reach them and try to put the cows in paddocks which have access to shade. Fans in buildings can aid with air flow particularly in areas such as the collecting yard or loafing spaces.
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