Implementing cow cooling has been shown to provide clear economic benefits in the hot, dry climates of the American Southwest as well as parts of Africa, Asia and the Middle East.

Heat abatement is effective in hot, dry climates

Dairy cows raised in “arid” or “semi-arid” climates are, on average, more greatly affected by heat stress than cows raised in cooler climates. However, because of the low relative humidity (RH), evaporative cooling is very effective.

For example, at 100ºF and 15 percent RH, an evaporative cooling system operating at 75 percent evaporation efficiency will reduce the temperature by almost 25ºF and the temperature-humidity index (THI) by about 8.3 units.

Due to its effectiveness, evaporative cooling often also makes sense economically. An economic analysis showed that implementing high-pressure misters mounted on fans can reduce the overall costs of heat stress by greater than 45 percent (including the annualized capital and operating costs of cooling systems).

Table 1 presents the typical number of heat-stress hours in three arid to semi-arid U.S. states and the estimated costs of heat stress under minimal heat stress abatement as compared to high-pressure misters mounted on fans.

Cooling in drylot shades and Saudi barns

Drylots with shade and Saudi-style barns are the most common dairy cow housing in arid and semi-arid regions.

Basic structure and layout

Drylot shades

In drylots, 45 to 50 square feet of shade should be provided per cow. Drylot shades are typically oriented north-south to maximize the distance their shadow moves during the day so that, as the animals move with the shade, the manure and urine they produce will be spread over a wider area and the abandoned ground can dry. The recommended height for drylot shades is 11 to 14 feet.

Saudi barns

Saudi barns are also constructed in drylots and are typically around 105 feet wide, with 11- to 14-foot eaves and a 2-to-12 to 4-to-12 roof slope.

They feature a central drive-through feed alley and feedlines that can be underlain by a concrete slab but elsewhere typically have dirt floors (Figure 1). One advantage these structures have over basic drylot shades is that the cows do not have to leave the shade to access the feedline.

In extremely hot locations, the bedding area is cooled with high-pressure (200 to 500 psi) misters, and sidewall curtains can be used to somewhat contain the cooled air and provide shade.

In this case, a north-south orientation may be advantageous to help keep both sides of the barn dry. In milder climates, some producers have chosen to forgo the installation of evaporative cooling and curtains. In this case, an east-west orientation provides better shade.

High-pressure misters and circulation fans

Because high-pressure misters mounted on fans have proven to be especially effective in hot and dry weather, several companies now market fan/mister assemblies. We will consider these combination systems as they are sold as opposed to discussing fans and misters as separate units.

The combination systems are often mounted below a structure’s eaves to blow in fresh air from outside. Alternatively, through-the-roof fan/mister assemblies pull in fresh air through an opening in the structure’s roof. If mist is injected into recirculated air, very good ventilation is necessary. Too much mist without inlet air does not lower the temperature and can lead to unhealthily wet conditions.

Eave-mounted evaporative coolers

Mounting fans and misters below a structure’s eave is especially compatible with drylot shades (Figure 2). Some of these are shade-tracking systems that offer the advantage of supplying cooling to the shaded area as it moves throughout the day.

Besides providing the cows more comfort, this feature spreads manure and urine over a greater area and eliminates the need for a curtain to block afternoon sun. In addition, this fan can be adjusted to blow mist into the loafing area where cows often rest at night.

Through-the-roof coolers

Through-the-roof coolers (Figure 3) pull fresh air through the roof and inject a high-pressure mist into it, cooling the air before it is blown onto the cows.

These systems have the advantage of bringing fresh air into the central areas of the barn and are ideal for Saudi barns, but they can also be used in conjunction with naturally ventilated freestalls and drylot shades.

Although recommendations vary by specific product, these units are typically placed about every 20 feet on either side of the central feed table (Figure 4).

Controls

Combined fan/mister assemblies usually rely heavily on a control system to function optimally. The control system measures parameters such as sun angle, wind speed, wind direction, temperature and relative humidity. These measurements help the cooling system focus cooling on the areas where the cows are most likely to be.

In addition, the control system can regulate the flow rate of water leaving the nozzle. This enables the misters to inject just the right amount of water to maximize evaporative cooling without wetting the bedding.

Some cooling should be provided as the THI exceeds 68. However, in an arid climate, setting the system to turn on at 68ºF may cause the system to operate many more hours than necessary. For example, at 20 percent RH, a THI of 68 corresponds to a temperature of 76ºF.

Holding pens and feedlines

In the holding pen and along feedlines, cooling can be provided by fans and low-pressure sprinklers. In well-ventilated feed and holding areas, mister/fan assemblies are also an option. In Saudi barns, care must be taken so that water applied at the feedline does not flow into the lying areas.

Priority

When available funds will not cover the costs of heat stress abatement in all desired locations, funds should be applied according to the following priority:

1. Shade for all milking and dry cows
2. Holding pen cooling
3. Exit lane cooling
4. Corral shade cooling
5. Feedline cooling
6. Covered feedline

Estimating resource use

The amount of electricity used by fans can be estimated by multiplying the power consumption of the fans’ motors by the typical number of hours per year the fans operate. When estimating electrical costs, note that motor horsepower is given in mechanical output and that the electrical input is always greater.

A typical 1-horsepower motor requires around 1 kilowatt of electrical power. The water used by a sprinkler system can be estimated in a similar manner. Simply multiply the system’s flow rate at its set point by the typical number of hours per year within each set point range.

Conclusions

Implementing cow cooling has been shown to provide clear economic benefits in arid and semi-arid climates. However, determining the practices that will optimize the combination of air velocity and evaporative cooling in terms of milk production, animal health and resource efficiency will require more studies.

This notwithstanding, current research has shown that high-pressure misters mounted on fans are very effective at reducing heat stress in open structures. Mechanically ventilated systems with evaporative pads can also lower the temperature but require totally enclosed barns.

While freestalls are more expensive than drylot shade pens, they may become more common with increasingly strict environmental regulations and in regions where the risk of severe winter storms is high.  PD

This guide is a climate-specific extension of the summary article “Dairy Cooling: The Benefits and Strategies,” which describes heat stress, its costs and consequences, and strategies for its mitigation.

Christopher Choi is a professor with the University of Wisconsin – Madison Department of Biological Systems Engineering.