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Conductive cooling as an alternative to cool down dairy cows
The typical cooling system utilized to reduce heat stress in dairy operations requires high energy and/or water usage. With the steady increase in electricity costs and reduction of water availability and increase in water usage regulations, passive cooling systems need to be investigated as ways to cool cows and reduce the utilization of water and electricity.
An experiment was designed to investigate the use of heat exchangers buried 25cm below the surface as components in a conductive system for cooling cows. Six cows were housed in environmentally controlled rooms with tie-stall beds which were equipped with a heat exchanger and filled with 25cm of either sand or dried manure. Beds were connected to supply and return lines and individually controlled. Two beds (one per each kind of bedding material) constituted a control group (water OFF), and the other four (two sand and two dried manure) used water at 7°C passing through the heat exchangers (water ON). The experiment was divided in two periods of 40 days and each period involved three repetitions of three different climates (Hot Dry, Thermo Neutral and Hot Humid).
Sand bedding remained cooler than dried manure bedding in all environments and at all levels of cooling (water ON or OFF). Bed temperatures were lower and heat flux higher during the Sand ON bed treatment. We also detected a reduction in the core body temperatures (CBT), the respiration rates (RR), rectal temperatures and skin temperatures of those cows heat stressed during the Sand ON treatment. Dry matter intake and milk yield numerically increased during the Sand ON bed treatment for all climates. No major changes were observed in the lying time of cows or the composition of the milk produced.
We concluded that use of heat exchangers is a viable alternative to systems that employ fans, misters and the evaporative cooling methods to mitigate the effects of heat stress in dairy cows. Sand was a better bedding material to use in combination with heat exchangers. Additional research is needed to investigate alternative ways to increase the exchange of heat through conduction. Future studies should investigate the benefits of placing the heat exchanger closer to the skin surface and further reducing the water temperature through mechanical cooling.
Keywords: conductive cooling, heat stress and dairy cow