Most dairies soak cows with potable water, and the amount used varies widely among farms (eg, 4.5-25.7 L/h per cow). In the coming decades, water is predicted to become increasingly limited. Therefore, in addition to mitigating heat stress, reducing water footprint is a major sustainability concern for the US dairy industry. Many recommendation can be found for how much water to apply for cooling but, until recently, evidence was lacking from peer-reviewed studies on live cattle. Earlier research used simulations, and a single study comparing different sprinkler flow rates soaked cows in the bedded area, which does not reflect common industry practice. Recent studies in a low-humidity climate varied the total amount of water applied by manipulating either the sprinkler flow rate or application duration. These studies demonstrated that soakers remove heat through additional mechanisms be- sides evaporation from the skin and coat and provided the first empirical evidence for the amount of water needed to cool cows effectively.                                                                             

Because latent heat loss does not rely on a temperature gradient between the animal and its environment, discussions about soaking typically focus on the cooling that occurs through evaporation from the animal after the water is turned off. Industry publications recommend that cows should be "soaked to the hide along the topline while not getting wet to the point of having water running off the sides "and that "sprinklers should wet the back and then stop the cycle to allow the water to evaporate prior to another cycle beginning. Additionally, dripping water has been associated with speculative concerns about mastitis, although no studies have shown a direct  link. However, when water (which is typically cooler than the skin) drips from the body, this removes heat. Along with the cooler microclimate that results when droplets evaporate from the ground and in the air, dripping water generates rapid reductions in skin temperature and respiration rate, which were reduced relative to unsprayed controls after a single spray application of 3 minutes (using >1.3 L/min)55 or 90 seconds (using 4.9 L/min). Longer spray applications (up to 13 minutes) resulted in greater reductions in these measures and body temperature was reduced at the end of single, continuous spray applications of 10 or 12 minutes, before the coat had time to begin drying. These results demonstrate that the cooling contributions of fluid convection and a cooler microclimate (indirect evaporation) should not be discounted. Although minimizing water use is an important concern, enough water should be applied to generate effective cooling. A single 12-minute spray application of 4.8 L or 4 repeated spray applications of 1.2 were insufficient to reduce body temperature. Furthermore, relative to those lower-flow nozzles, higher-output sprinklers better cooled the microclimate and reduced the respiration rate. Nonetheless, applying more water results in a pattern of diminishing returns for cooling. In a lower-humidity climate, the optimal quantity seems to be approximately 4 L per spray application (which can cool 2-3 adjacent cows at the feed bunk) when water was applied 4 or 5 times per hour. Regardless of whether cows are soaked only enough to wet the back or if water drips from their sides, the coat takes 14 to 16 minutes to dry, on average. Drying time is reduced in warmer or windier conditions, supporting the common practice of spraying more frequently when air temperatures increase. These findings also suggest that although a single spraying session has the potential to suppress body temperature for a while afterward spray applications should be less than 15 minutes apart to generate consistent cooling throughout the day (Box).                                                

In terms of nozzle selection, some investigators have expressed concerns about smaller water droplets landing on the hair coat instead of soaking through to the skin. Some have speculated that smaller droplets may form an insulating barrier of water on the surface of the hair coat, trapping heat and exacerbating heat stress. This idea, however, may be a misinterpretation of earlier statements that when droplets rest on the coat instead of reaching the skin, evaporation will transfer heat away from the coat rather than from the body surface, resulting in less efficient cooling. recent study evaluated the cooling effects of droplet size within a given flow rate, with the prediction that larger droplets would cool more effectively because they are less likely to evaporate before landing (although this could cool the microclimate, similar to misting) and might better penetrate the hair coat -

 Guidelines for low-pressure soaking at the feed bunk