Cows exhibit individual preferences when making choices about how to cool off during summer heat
Dairy cows like it cool, and farmers have responded by installing sprinkler and misting systems to dampen hot weather's effects on their herds. Given the opportunity, however, cows apparently prefer to choose for themselves when and how they get wet.
A Holstein cow's comfort zone can vary between five and 20 degrees Celsius. As the temperature gets above 25 degrees, especially if the relative humidity is high, signs of heat stress may start to show up-lower dry matter intake and reduced milk production. Prolonged heat stress can affect breeding efficiency, as well.
Keep this in mind if you keep more cows in the barn during warmer months. Overcrowding raises the barn's heat load and may prove a drag on production.
You have several ways to reduce the effects of warmer temperatures. Providing plenty of drinking water and making it easily available for cows is an excellent first step. Access to shade, good ventilation and air movement are other simple means to reduce heat's impact.
You can also use water to cool your herd. Sprinkler or misting systems are fairly common in large New Zealand and U.S. herds. Most sprinkler systems are hooked up with fans. Evaporation induced by the fans enhances the water's cooling effect. Dairy farmers usually install these systems where the herd congregates, such as waiting areas before milking or above the cows at the feed bunk.
Studies indicate wetting a cow's back effectively reduces its respiration rate, or panting, and body temperatures-both indicators of heat stress. Other studies have shown cooling cows with water results in increased feed intake and milk production when compared to control groups.
Aversion to sprinklers
Despite the effectiveness of cooling with sprinkler systems, some cows show behaviour indicating an aversion to it. For example, animals will position their heads outside the sprinkler to avoid getting their faces wet. Others will lower their heads in response to overhead water or avoid the water altogether whenever possible.
Most dairy systems offer water cooling to their herds in close proximity to other resources such as feed or lying areas. This makes it difficult to tell whether cows would use the cooling system voluntarily without any other incentives.
Cow shower constructed
A recently published study conducted during the summer of 2008 examined the voluntary use of a shower by cows when this cooling system was located away from other resources like the feed bunk or water trough. University of California Davis researchers constructed a shower stall consisting of a platform equipped with pressure sensors and an overhead frame with two standard shower heads.
When the sensors detected a cow's weight on the platform, water flowed from the shower heads. Once the cow left the platform, water flow would stop.
Since the shower stall was located away from other resources, animals would need to go deliberately into the stall to get wet. A control group was exposed to the same conditions without access to the shower stall.
The researchers used 12 pairs of non-lactating Holstein animals for this study, and recorded and evaluated climatic, physiological and behavioural measures.
The group with access to the shower stall used it an average of three hours per day. Most shower visits were fairly brief at less than a minute, but some went on much longer.
Shower use variations may indicate degree of heat stress. The researchers used cameras to monitor which parts of the cows would get wet since the animals controlled this factor. Although there were substantial variations among animals, necks and flanks were the most common areas exposed to the shower.
The cows predominantly used the shower during the warmest part of the day and increased use with warmer weather, as shown in the graph on page 38. During the experiment, shower use increased by 18 minutes per animal for everyone degree Celsius increase in temperature.
The control group, without access to a shower stall, spent more time at the water trough. Open-mouth panting was observed only in control group cows.
This study demonstrates substantial variations of shower use among animals. This may indicate individual animals experience heat stress to a greater or lesser extent than their herdmates. Some may spend great amounts of time in the shower stall while other cows may not use the system at all.
Several factors may influence the willingness of a cow to use the system. Among the factors researchers identified were: prior experience, water droplet size, water pressure, water flow rate and the cow's control over which part of her body got wet.
Although using a shower stall is not a common cooling method on dairy farms, this study demonstrated cows can voluntarily use water cooling as a means to reduce heat stress.
This article first appeared in the Ruminations column of The Milk Producer Magazine in August 2011.
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