Summary
Water is the most important element for the survival of cattle. Water plays an important role in many essential body functions, including digestion and regulation of body temperature. Limitations on water intake depress animal performance quicker and more drastically than any other nutrient deficiency (Boyles, no date). Increasing water uptake can improve feed conversion, reduce illness, improve cooling ability and improve body functions. Supplying good quantity and quality water encourages increased water uptake that is fundamental to minimising heat stress and maximising performance.
The ideal ambient air temperature for cattle is 5-25oC (Tdb). In this temperature range the cattle's natural cooling is by heat transfer from the hide into the atmosphere and from respiratory ventilation. With Bos taurus cattle being a species that originated from temperate climates, its temperature regulation system is better suited to maintaining temperature rather than cooling in temperatures above 25oC. The heat stress threshold temperature for Bos taurus cattle is 25oC (Hahn et al., 1997). When the ambient temperatures rise above 25oC, the symptoms of heat stress start to become evident though they may not be visible until significant heat loading occurs. High humidity, low wind speed and/or solar radiation also effect heat stress. In extreme situations where ambient temperatures exceed body temperature this process is reversed and cattle actually directly gaining heat. The effects of heat stress have a significant effect on beef production. Cattle need to be consistently gaining weight for a feedlot to be profitable. Any factors that reduce or inhibit weight gain need to be addressed and heat stress is one of these factors. When cattle become heat stressed they have a reduced feed consumption, which in turn reduces their performance. The probable reason for this is the inability of the animal to dissipate its body heat to a hot environment and the alternative is to reduce heat production through lowered feed consumption (Lofgreen, 1975).
There has been a lot of research conducted with regard to heat stress in cattle (Flamenbaum et al., 1986, Hicks et al., 1988, Gaughan et al., 2001). The majority of this research has been on the effects of shade, diet modification, microclimate and development of an index for heat stress. There has been little research undertaken in Australia on the effects of drinking water temperature and cooling stock by wetting. Supplying cool water for drinking has a limited direct cooling effect. Other benefits associated with drinking cooler water have a significant indirect impact in reducing heat stress. This includes; increased water uptake, improvements in feed conversion, reduced illness, improved cooling ability and improved body functions (Lofgreen, 1975). It also maximises the cattle's natural cooling ability through sweating, breathing and decreasing body temperature. Alleviating heat stress in cattle can be achieved by reducing the heat load (shade) or by dissipating heat from the animal to lower its body temperature (spray cooling). If the incoming solar radiation is 39MJ per day, shade reduces this heat load by 70%, or by 27MJ. It is still possible to have heat stressed cattle with shade. In such a circumstance, spray cooling may become important. Spray cooling dissipates a further 15MJ of energy from the system per application (where ambient air temperature 35oC, water temperature is 25oC and relative humidity is less than 60%).
Evaporative cooling ponds (ECP) have the most potential as a cooling system for providing cool drinking water to feedlot cattle, as it is the most cost-effective and efficient cooling system. There needs to be further basic research to determine operating constraints and possible heat dissipation from the system. The pond system also can act as a balancing storage, with cooling and a reduction in evaporative losses enhanced by shading. Most feedlots would already have a water storage that could be used as an evaporative cooling pond. While the supply water temperature needs to be lowered in some cases (for example, bore supplies), there are some trough designs and practice measures that could be adopted to help reduce the heating of water caused by reticulation systems heating water.
