Heat Stress Unveiled: A Deep Dive Interview with Dr. Mike Wolf

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Heat stress in dairy operations is becoming more a topic of greater awareness in recent years. Some is attributable to the climate change observations.  Other reasons are centered around consolidation of the dairy industry with higher cow numbers per operation.  Pasture based systems have long been a source of low-cost production with resulting lower yields per animal.  This is resulting in some dairy markets finding they cannot produce enough domestic dairy products and are importing their needs.  This has resulted in more confinement type operations.  The goal of these more intensive production systems Is to bring the best parts of the pasture production methods indoors and eliminate the downsides of traditional pasture-based systems.  Even pasture-based systems during off growing season times of the year require some degree of indoor housing and ventilation.  The same targets for animal welfare in cow comfort, health and productivity need to be met.  Another reason is the genetic capability of today’s dairy cow has increased capacity of milk production per animal.  The demand for dairy products seems to be increasing. As countries develop higher living standards with developing middle classes, food security concerns, especially since the Covid pandemic and increased geopolitical tensions is driving dairy production in these areas. A dairy cow is a tremendous metabolic athlete, which brings us to the focus of VES-Artex in promoting cow comfort elements within the cow’s environment.  This includes the overall barn design and how the various cow comfort elements fit into her housing environment.  These include freestall & pack barns, ventilation, lighting, and cooling strategies.

Traditional natural ventilated facilities rely solely on the wide variation of wind direction, speed, and duration.  Many legacy barns lacked adequate roof pitch to enhance adequate air exchange.  Many times, the wind is calm and barn ventilation is entirely dependent on thermal buoyancy off the animals to drive the ventilation.  In some situations, the traditional barn designs did not adequately meet the exchange rates needed, but these barns were designed for a dairy cow producing less than half what cows are capable today.  As dairies grow additional surrounding structures begin to impede the traditional natural ventilation strategy.  The next step in ventilation was the addition of recirculation fans along with soakers at the feeding areas.

The recirculation fan strategy a good first step up from completely natural ventilation but does not guarantee the rate of air exchange within the barn.  This led to what we refer to as tunnel barn designs, where the air exchange is guaranteed.  This requires the closing of the barn side walls and adding exhaust fans to create the tunnel effect. The philosophy was to create a one minute or greater air exchange in the barn with the idea the heat, humidity and noxious gases would be more than adequately removed and create air speeds at the cow living space of 2 mph or 1 m/s.  Initially the 1 m/s was thought to be enough to cool the cow.  Subsequent research at Kansas State, Arizona State and elsewhere confirmed 1 m/s was the minimum threshold to cool cows under heat stress conditions.  The target has become closer to 2-3 m/s depending on the local climate.  Higher heat & humidity areas require the upper end of this target. This is where VES (now VES-Artex) realized the air flow from many fans on an end wall did not deliver the target speeds of 1-2 m/s in the cows living space especially the freestall or pack area.  Initially baffles were placed perpendicular to the air flow within the barn to segmentally accelerate the air flow at the cow level.  We quickly discovered this was not an efficient way to get the desired flow to the cow since air will follow the path of least resistance which meant the air flowed quicker into the feed delivery lanes and scrape alleys.  The speed at the cow occupied zone was quite inconsistent.  Air followed the path of least resistance, and these early designs were not delivering this level of air flow required to the cow.  The use of baffles in tunnel ventilated barns is no loger the preferred method of enhancing air speed in the cow’s lying area.  We as a company learned that the one-minute air exchange was not necessary, so we brought some of the exhaust fan capacity in over the cows as large 2 meter (6 foot) louvered recirculation fans over the cow’s resting space.  These louvered fans targeted the bulk of the air coming out of the fan to the less than 2-meter height occupied by the cow.    

This type of powered ventilation strategy is incorporated in dairy facilities around the world.  This also includes crossvent designs where the air flow follows the longitudinal axis of the cow rather than a perpendicular flow in a freestall barn.  The purpose and goal with these designs is to deliver fresh air efficiently and effectively into the cows occupied zone.  It actively removes heat, humidity & noxious gases while providing sufficient air flow for cooling while incorporating either soaking, high-pressure fog or both appropriate for the local climate conditions.  There are webinars on the VES-Artex website covering these barn types in more detail including pros and cons of these approaches.

VES-Artex has promoted a newer method of ventilation of adult cow facilities, including natural ventilation with recirculation fans systems, with the addition of a fresh air injection fans.  This design uses a limited number of fans driving fresh air into the barn with the recirculation fans forcing the fresh air down to the cow’s living space.  These fans run on a variable frequency drive to modulate the air volume being injected into the barn as well as the speed of the recirculation fans to achieve a comfortable environment for the cow year around.  The contaminated air and heat will exit the barn through roof ridges, side/end walls or space boarding.  This concept is available in more detail in a VES-Artex webinar.  This design can be used across a wide size range of dairy facilities. Our target is always to primarily ventilate the cow and secondarily ventilate the barn.  We have found we can properly ventilate wide and long tunnel ventilated barns with the fresh air injection concept.

Another often overlooked area on the dairy regarding ventilation is the parlor/holding.  Even pasture-based systems can benefit from assuring there is shade, air flow and the use of soaking to cool the cows at each milking opportunity.  With the proximity of the cows in these areas, six times as much heat per square foot of area is being produced in the holding pen area.  Additionally, there is less surface area to release the heat of the animals to the environment.  This necessitates the addition of recirculation fans and preferably soaking to adequately cool the cows during the time in this area.  Early pregnancies can be lost from this brief period of heat stress even though the duration of her day might be in a very well-ventilated environment.

The dairy industry has made huge strides in reducing its carbon footprint over the years.  The use of already more heat tolerant breeds such as the Jersey or Holstein/Jersey crosses is already quite prevalent in the industry.  In the future the promotion of more heat tolerant genetics in the breeding programs such as the smooth hair coat gene in the Holstein breed will reduce cooling costs by raising the threshold where more aggressive mechanical ventilation is needed. The mitigation of losses due to heat stress will always be an ongoing challenge for the dairy industry across all the widely varying climates around the world.  Direct drive motor fans are currently an industry wide common development.  The elimination of belts and tensioners reduces cost of production, lower maintenance costs and extend product lifetime.  Another coming product on the horizon is water saving modules that activate when the cow is present rather than just running on a time schedule.  VES-Artex is continually seeking development of energy efficient fan designs combined with control technologies to reduce the carbon footprint per liter of milk produced.  VES-Artex has their own in-house test chamber to quickly evaluate new designs and bring to these products to market.    

Thanks for this opportunity to communicate with your members.


Michael J. Wolf DVM

Consulting Veterinarian VES-Artex