Cooling dairy cows using water sprays
Cows don't like the heat - they don't have as good an ability to cope with high temperature as they do with low temperature. And when we have a few hot days in a row like right now, you will notice the physiological effect that the heat has. A lot of our dairies have fans placed throughout the cow sheds to bring in and distribute fresh cool air. I've been looking up a couple of papers about the use of water sprays to help cows stay cool, which is likely to be a useful next step in tackling the effects of heat stress.
The Chen paper looked at what effect the flow rate and droplet size had on the cooling success. They measured cooling success using skin temperature, respiratory rate and core body temperature. They found that, contrary to popular belief, water droplet size had no recordable effect. There was thought that bigger droplets had a greater effect as it gave better hair coat penetration, but it wasn't seen in this study. And on flow rate, they found that the significant increase came from a flow rate of 1.3L/min. While increases above this rate did improve the cooling of the cows, the effect was very small and probably not worth the increased cost in terms of water usage.
The Legrand paper used a voluntary cow shower - with the cows choosing when and for how long to use a sprinkler system to cool off. The cows with access to a shower system had a lower core body temperature compared with cows not given the opportunity. The cows who could use a shower also spent less time standing at the water trough. An interesting finding here was the variability between individuals of use of the water shower: some didn't use it even though they were given access, others stood in it for 8 hours in a 24 hours period!
It might seem a lot of trouble and expense when we don't see the very high temperatures that other dairying areas of the world sometimes see, but the top end of the Comfort Zone for cattle is 25oC and we would get to this temperature in a cattle house more often than it might appear. Once we get to this temperature, the cows will be reducing movement and rumination to reduce heat production as well as trying to increase heat loss by energy consuming activities like panting, drooling and increasing skin blood flow. This all comes at a cost to efficiency, so we should look to make these cows more comfortable by lowering the temperature below the 25oC upper threshold.