Heat Abatement Options: Choosing the right cooling strategy
August 18, 2020
By Michael J. Wolf, consulting veterinarian, VES Inc.
On dairies around the world, the challenge of keeping cows comfortable and avoiding heat stress is one of the greatest health challenges dairy producers face. It can also have considerable ramifications on overall production, operational profitability and long-term herd health.
One of the most common issues we find on dairies with heat stress during peak season is the lack of strategically designed heat abatement systems. Depending on geography, climate, cow species, or even herd size, there is not a one-size-fits-all heat abatement approach. However, what does exist is the marriage of science and engineering to combine the right heat abatement strategies for your operation.
In the following article we will unpack some of the most popular heat abatement strategies and look at the type of environments where each of them works best or may not be an appropriate solution. No matter the location or the strategy, producers must first start with proper fresh air flow; let’s start there.
Fresh Air, First
Any proper heat abatement solution starts first with getting fresh air into the barn, and onto the animals in their beds. And the good news is that the technology used to do so is appropriate in nearly any environment and is considered a highly economical solution for achieving a successful heat abatement program.
Heat Abatement (n.) – The act of reducing or eliminating heat stress. (Cooling cows)
At the most basic level, the goal is to get fresh air into the barn, direct it to the cow level, then remove heat, contaminated air, and gases which come from elements such as TMR rations, manure, urine, and even the cows’ breath.
At VES our target is to achieve an Effective Cooling Velocity (ECV) of between 4 and 6 miles per hour over 80 percent or more of the cow’s living space – especially in stall beds where we want them spending greater than 50% of their day. Additionally, it is absolutely crucial to have a ECV of at least 2 miles per hour anywhere in the cow’s living environment. During peak heat stress conditions, the faster the air velocity, the better.
Effective Cooling Velocity (n.) – The measure of the speed of an airflow when it reaches the cow, rather than when it leaves the fan.
To hit the target velocity we use a combination of the following:
- An inlet source – such as an open end of the barn, a retractable curtain, or powered fan(s) which we call positive pressure fan (PPF) – that matches that of the exhaust capacity.
- ECV recirculating fans (ECV)
- Air flow ratio exhaust fans (AFR)
Appropriate Inlet Selection
Selecting the appropriate inlet source to deliver fresh air into the barn in a straight, controlled wave is a critical building block for proper heat abatement. Historically, dairies relied on natural ventilation to provide air flow. Natural ventilation, however, does not always create an optimal environment for your animals due to inconsistency in intensity, duration, direction of wind or air flow, and other external environmental factors. Instead, VES leverages inlet sources including retractable curtains, and a variety of different fans – used depending on the design and layout of the barn environment –to provide strong, consistent, steady air flow into the barn.
Inlet sources such as a roll curtain or a combination of both curtain and powered fans based upon your geographical climate and seasonal differences are also common; however, fully enclosed barns with Positive Pressure Fan inlets minimize the variables of the external environment and provide significant control for your animal’s microclimate.
Regardless of the chosen inlet source the primary objective is to introduce fresh air into the free stall barn and other areas where cows congregate such as the parlor and holding pen, where temperature spikes and heat stress can wreak the most havoc.
Effective Cooling Velocity Fans (ECV)
Once fresh air is in the barn, ECV recirculating fans are used to direct a wave of air over the free stalls and drive air down to the animal level, achieving our goal of cooling air velocity. Much like the positive pressure fans, these fans are virtually universal in their application around the world.
Large recirculating fans, in combination with baffles in some cases, help to strategically direct air through the animal’s environment towards the exhaust. Recirculating fans are also critical components of achieving optimal air speed for using soaker and high-pressure fogging strategies in certain regions.
Exhaust Fans (AFR)
Getting warm, humid air out of the barn is as critical a component of achieving cow comfort as any other piece of the puzzle. Without appropriate exhaust systems in place, the degradation of air quality from noxious gases sources such as ammonia, nitrous oxides, hydrogen sulfide etc. from urine, manure & feedstuffs continue to accumulate along with heat and humidity generated by the cow.
Exhaust fans take that contaminated air and proactively drive it out of the barn, creating a clean, cool air environment. Just like positive pressure fans and recirculating fans, exhaust fans are highly economical and appropriate for almost all dairy environments.
The next component in achieving cow comfort under high temperature conditions is what we refer to as evaporative cooling. While cows do naturally sweat to help cool them, it is not nearly as effective for keeping the animal below her CBT (core body temperature) of 102.2, where heat stress has exceeded her ability to maintain a normal CBT by seeking air movement, increased standing time, increased respiratory rates and water consumption.
Thermal Heat Index (n.) – A measure that accounts for the combined effects of environmental temperature and relative humidity on cattle / livestock to assess the risk of heat stress and prevent major effects. The THI for the cow unlike the human Heat Index can never be greater than the surrounding air temperature. Since the respiratory tract constitutes about 30% of her overall cooling capacity as humidity rises the ability of her to release heat through the water vapor she exhales diminishes dramatically. Inspired air humidity of 80% or greater basically stops this heat exchange potential.
Soaker systems are the most universally used evaporative cooling technique amongst dairies globally. In most systems, an in-barn temperature sensor assesses temperature and turns the soakers on at the appropriate volume. Depending on the temperature, the soaker system will run more often, while also working to make sure that as much water as possible is being directed onto the cow’s skin.
At VES we recommend soaker lines at the feed rail and holding pen areas then optionally in the parlor – both on parallel and rotary parlors after milking equipment is attached and again immediately as they exit the parlor. Once a cow is soaked for between 30 seconds and a minute – up to two minutes in some extreme cases – the strategic air flow is directed to the animal creating a cooling effect.
Whenever possible, soaker systems are designed where we can direct the evaporative cooling effect only where we need it – where the cows are. This helps alleviate any increases in manure slurry, which can lead to other health issues such as mastitis, while also reducing the need for extra udder sanitation during the cleaning process and overall barn cleaning, as well.
A downside of soaker systems is water use. At times, the soakers will be running when there are no cows in the vicinity to be soaked, so water can fill alleyways and increase the amount of manure slurry in the barn.
Another strategy considered for evaporative cooling is high-pressure fogging, which uses microscopic water droplets that quickly evaporate in the air, dropping the temperature of the wave of air while creating a cooling effect.
This is a very good solution for climates with low humidity, where the added water droplets are not going to cause spikes in THI when added to the already hot and humid air. In most cases, high-pressure fog is most appropriate in environments with humidity below 55 percent. That’s because the level of investment to install the fogging system infrastructure – piping, pumps, nozzles – isn’t justified as quickly due to the inability to use the system during the hottest, most humid months of the year.
However, in more arid climates, high pressure fog can be an extremely effective strategy. When combining appropriate ECV with a high-pressure fog system, the total THI score can be reduced significantly, potentially moving a cow from a zone of heat stress to relative comfort.
At VES, misting is not a technique we use or would recommend to dairies. The larger droplet size in comparison to High-Pressure Fogging does not dissipate efficiently to get the intended evaporative cooling effect. In many cases, the mist will fall on the cow, but does not soak her to the skin, creating a wet blanket that actually causes her core body temperature to rise.
Misting can also lead to wet or damp bedding areas which can increase the risk of mastitis. Research has also shown cows prefer a dry bed versus a damp bed, in terms of overall comfort.
A mainstay in the poultry and swine industries, cooling pads have been deemed ineffective for dairy operations. For a period of time before high pressure fog and soaking systems were developed, cooling pads were, but a variety of issues have led to them falling out of favor.
The first issue is maintenance. Cooling pads require several hours each day to dry out, otherwise, they will begin to develop molds and accumulate unwanted mineral and limestone deposits. Additionally, they are difficult to get air through, so barns end up running more fans than needed.
What You Need to Remember:
– Fresh air is king. Achieving the right Effective Cooling Velocity is your top goal for heat abatement.
– A minimum airflow of 2 mph anywhere in the cow’s living environment is also critical to achieving peak cow comfort and minimizing heat stress risk. At VES, we target an ECV of 4-6 mph over 80 percent of a cow’s living area; this is considered optimal.
– Pair the right evaporative cooling approach for your climate with effective cooling velocity and your cows will be much more comfortable.
– If you are in an area that experiences high humidity during the warmest parts of the year, then a soaking system is likely the best approach. In more arid climates, high pressure fog or a combination of high-pressure fog and soaking can be highly effective.
– Connect with VES dairy experts who can examine the climate and weather patterns in your geographic area to help determine which heat abatement strategy is both cost effective and cooling efficient for your operations and your animals.