Heat stress has been estimated to cost the dairy industry $897 million, and one of the most effective methods to alleviate heat stress is to cool the cow directly using low-pressure soaking. With a thermoneutral zone of 40°F to 70°F, dairy cows are very susceptible to heat. This article will focus on feedlane soaking but will also touch on other areas where soaking is used.
Soaking characteristics
Typically installed at the feed alley, soaking consists of a main-line pipe delivering water to nozzles that typically output around 0.5-1.5 gallons per minute (GPM) at pressures of 15-25 pascals (Pa).
Outside of the feed alley, the type of nozzle used can be similar to those used in irrigation (or other methods of delivering a large area of water coverage in the holding area), shower heads in the parlor stalls and, in some cases, return lanes.
In very hot conditions, producers have also adapted soaking areas designed specifically with high airspeeds and large amounts of water, which cows visit multiple times per day.
Soaking cools the cows at first by having water in contact with the skin. Then, it cools the cow as the water evaporates close to the skin. It is important that the droplets are large enough to penetrate the hair coat to get the largest cooling benefit for the cow.
This strategy is most effective when paired with high airspeeds by adding fans over the stalls and, in more extreme heat, fans over the feedlanes. Recommended cooling airspeeds range from 200-600 feet per minute, depending on the climate. Other sources claim that slower speeds, such as an airspeed of less than 200 feet per minute, improve heat transfer as the cooling effect is released more evenly over time.
Physiological effects on cows
There are many studies on the positive effect of low-pressure soaking as a heat abatement tool. Rather than cite specific studies, a high-level summary can be found in this article by Jennifer M.C. Van Os, which states the benefits of direct soaking as:
- Reduced body temperature, respiration rate and skin temperature
- Increased feeding time and dry matter intake (DMI)
- Increased milk yield
- Reduced insect-avoidance behaviors
When and how much to soak?
You will typically find most systems begin soaking at 66°F-70°F. The current gold standard of temperatures for cooling seems to be 68 temperature-humidity index (THI) – often used as 68°F because at this temperature the THI will max out at 68 when humidity is 100%.
Research on heat stress has been reducing the recommended cooling temperatures and THI levels when one should start heat abatement technologies. In the publication “Quantifying Heat Stress and Its Impact on Metabolism and Performance,” Robert J. Collier et al. challenged that figure, stating that “... our data indicates that dairy cows producing more than 35 kilograms (77 pounds) per day need additional cooling when minimum THI is 65 or greater or when average THI is 68 for more than 17 hours per day.”
New studies with behavioral patterns beyond physiological responses – such as brush use and other unnecessary activities, often called luxury behaviors – are showing that cows may show signs of stress at THIs much lower than 68.
Water consumption
While we want to maximize cow comfort, we must also consider how much water will be added from the various soaking systems to the manure storage system.
Even though the cost of water is relatively low, water consumption for soakers is a function of activation temperatures, and almost all the water from soaking enters the manure flow. Depending on the manure management system, this can be a nuisance or an extremely costly issue.
Let’s do a quick example on a three-row pen with 85 stalls and assume a stocking density of 1.18, so the pen has 100 cows. The feed alley is roughly 135 feet, meaning it will have 22 soaking nozzles (at 6-foot spacing). Using a conservative estimation of around 0.7 GPM soaking nozzles and the following soaking schedule with one-minute soaking events:
- A downtime of 15 minutes (four soaks per hour) from 68°F-72°F
- A downtime of 10 minutes (six soaks per hour) from 72°F-82°F
- A downtime of six minutes (10 soaks per hour) from greater than 82°F
In Madison, Wisconsin, the total water added from soaking, based on 2023 weather data and this soaking schedule, would’ve been around 9,300 gallons per nozzle. According to the Adult Cow Housing Module by the Dairyland Initiative, the suggested minimum manure storage per 100 cows is 1 million gallons per year, meaning the soaking system adds approximately 20% of the minimum manure storage.
This is a simplified and conservative example, but it should highlight the magnitude soaking has on the overall system design for a farm’s manure management if not accounted for. Each degree where soaking is added earlier will significantly increase the water added to the manure system.
To improve water savings and sustainability, a sensor-based design where a soaking unit operates on cow presence rather than time is recommended.
Sensor-based soaking
Sensor-based soaking (activating soaking units based on cow presence rather than time-based units) has the potential to significantly reduce water use.
According to a 2010 study by A. Gomez and N.B. Cook, cows spend 83% of their day – or 19 hours – away from the feedlanes and alleys.
Suppose soaking is only activated when a cow is present. In that case, there is the potential to save up to 83% of the water used if the unit was on for 24 hours since that is the time cows are away from areas where soakers are present (not including the holding area).
The system, however, doesn’t operate throughout the entire day, and from our initial research using our sensor-based soaker, we are seeing water savings of 50% on average, with some days saving up to 70%.
There are already industry examples of sensor-based soaking utilizing various technologies such as RFID, image-based detection and ultrasonic detection. There are also academic studies, such as this article by Gustavo Mazon et al., which tested an autonomous soaking system using RFID and concluded that its adoption might allow for reducing water waste.
Voluntary soaking is positively correlated with milk yield, as higher-producing cows use the soakers more, which sensor-based soaking would mimic.
As technology continues to become more accessible and more robust, I believe sensor-based soaking will become the norm. Especially if water use becomes more regulated in the future.
Summary
The most common soaking systems cool the cow by wetting the skin and then evaporating at the skin assisted with airspeed generated by fans.
Typical recommendations are to begin soaking at 66°F-68°F, but the average soaking times and water use should also be evaluated to create a soaking schedule your facility can handle. Make sure your intake pipe has enough pressure for the soaking design and that your system can handle the water demand, and consider a sensor-based solution to reduce your water consumption.
Soaking is one of the most powerful tools against heat abatement and new developments both in industry and academia are making it more sustainable.
References omitted but are available upon request by sending an email to the editor.
