Dairy Cattle Heat Stress
Heat Stress Abatement Techniques for Dairy Cattle
Dairy cows generate a lot of heat. A cow milking (120 lbs) 54 kg of milk per day generates about 6,300 BTU (British Thermal Units) per hour – twice as much heat as a cow producing only (40 lbs) 18 kg of milk per day (3,300 BTU/h), and 19 times the330 BTU/h a human produce at rest.
Productive dairy cows may experience heat stress when the Temperature Humidity Index (THI) is 68 or greater. In ‘more humid’ climates this can occur at temperatures as low as 72oF. Heat stress can be reduced by slowing heat gain to the cow, and improving heat transfer rate from the cow. Basic heat stress abatement techniques for Dairy cattle include Shade, Air, and Water – (SAW)
Techniques to reduce cattle heat stress
Dairy cattle may experience heat stress when the Temperature Humidity Index (THI) is 68 or higher. In ‘more humid’ climates this can occur at temperatures as low as 22 °C (72 F°). Heat stress in cows can be reduced by slowing down the warming of the cow and increasing the rate of heat transfer from the cow with animal cooling and cooling systems. Dairy cattle heat stress can be calculated index below.
THI Temperature Humidity index calculation
THI =0.8*T + RH*(T-14.4) + 46.4 where T = ambient or dry-bulb temperature in °C and RH=relative humidity expressed as a proportion i.e. 75% humidity is expressed as 0.75.
The “Temperature-Humidity Index Program (SINEP)” has been prepared in order to predict the time periods during which temperature-humidity stress may occur, which causes significant yield losses in cattle breeding in our country, as it is the case all over the world, thus enabling our farmers to take the necessary precautions and minimizing their losses.
Excess moisture can become a major problem for livestock. According to the University of Kentucky Department of Agricultural research, animals will be bothered by hot, dairy cattle heat stress when the temperature index reaches about 90 degrees, but the main issue is humidity!!!
- Warm air holds more moisture than cold air
- Warm air is actually lighter than cold air (known as Avogadro’s Law)
Moisture sources in covered barn buildings must be prevented or eliminated. A good ventilation system should carry enough fresh air into the building.
- Animals release a large amount of moisture into the air as they breathe, and if this moisture is not properly ventilated, it creates high relative humidity.
- High humidity tends to form biofilms in barns that allow bacterial growth, extensive bacterial colonies, and the production of other corrosive acids.
- Ammonia gas found in animal environments easily combines with this moisture and a chemical, ammonium hydroxide, is formed.
- The released moisture provides an environment where dust, acids and gases commonly found in animal environments react, accelerating the corrosion rate considerably.
- Imagine a cloud of moisture floating up from the barn floor.
Basically, condensation occurs at night when the temperature inside a building is warmer than outside. Warm, moist air rises and cools with the cold roof, as it cools, it cannot hold the moisture and condenses and falls like raindrops. :
Often, businesses tighten a barn to save money. Unfortunately, this reduces the ventilation rate and increases the building temperature and humidity level. In fan-ventilated barns, ensure that at least one exhaust fan is running to continuously extract the required humidity. Naturally ventilated barns require a constant exchange of air to control humidity.
Basic heat stress reduction techniques
Cows accumulate heat rapidly while lying down (about one degree F (0.5 C0) per hour of rest) and dissipate heat when they stand (about a half a degree F (0.25 C0) per hour). As temperature increases, the number of lying bouts per day stays the same, but lying but duration decreases. Daily lying times may rapidly fall to as low as 6 hours per day during times of heat stress as dairy cows stand more and thermal pant to cool. Cows may exhale more than 4 gallons (15 liters) of water from their lungs per day! This significant behavioral change, coupled with the physiological changes occurring due to heat stress, are responsible for the clinical signs we associate with hot weather. Dairy cattle heat stress tools are:
SHADOW, AIR, and WATER – (includes GHS)
Shadow
Protecting cows from direct solar radiation helps to lower their body temperature and respiratory rate. Shade areas can be provided by trees, buildings or other structures. Roofs and canopy structures must be at least 12 feet high and in the correct position. Buildings and covered feeding areas should generally be oriented east-west to minimize the effect of sunlight during the day. Pasture or dry multi-shade structures in the north-south position the shade shifts from west to east, which may be sufficient to keep the rest area dry.
Air Exchange
We need to ventilate the barn at around 4to 8 air changes per hour. Meanwhile, during the summer, the
requirement for clean fresh air to ventilate the barn continues at a greater rate of around 40 to 60 air changes per hour.
An air exchange every minute or less during the summer months is essential to remove moisture, gases, heat, and other pollutants from animal space. Without a proper air exchange other heat stress abatement techniques will not work effectively.
Mechanically ventilated dairy buildings use exhaust fans and properly sized and placed inlets throughout animal space. Tunnel ventilation can provide a rapid air exchange – typically less than 45 seconds – in tie stall barns.
Naturally ventilated buildings depend primarily on wind speed and direction to drive the air exchange. Buildings with high, side and end walls fully open to resting cow level create a preferred ‘pavilion-like’ design during the summer.
When the warm weather exchange rate in naturally ventilated buildings is challenged by topography, up wind obstacles, or building limitations, well designed tunnel or cross ventilation systems can be used provide the necessary air exchange.
Air circulation
Turbulent air movement around cows increases convective heat transfer, enhances evaporation, and minimizes “hot spots”. Air speeds of 3.5 to 5 miles per hour (mph) are preferred in resting, feeding, and holding areas.
36 to 52-inch diameter axial circulation fans can provide excellent animal space air movement. To be effective fans placed in-line must be no further than 10 times their diameter apart. For side-by-side applications, place fans two to three times their diameter apart.
Large high volume, low speed (HVLS) fans can also provide air movement at cow level, but they must be placed over the animals, and usually no more than twice their diameter apart.
Natural and mechanical Air circulation
In summer, at least a minute of air exchange is necessary to remove the humidity, gases, heat and other polluted air from the area where the animals live. Other heat stress reduction techniques will not be effective in the absence of adequate air exchange. Dairy cattle heat stress is main concert to fight.
Roof slope
Roof slope also affects the performance of a naturally ventilated building. A proper roof slope enhances air mixing within the building and the ventilation rate through the building. An ideal roof slope is 4:12 (rise: run). A shallow roof slope less than 3:12 or a flat ceiling will reduce air movement due to buoyancy forces. This results in stagnant air spaces, reduced ventilation rate, and increased moisture, heat, gas, and odor accumulation. A steeper roof slope can enhance the upward air movement due to buoyancy, which increases the air exchange rate. However, roof slopes greater than 6:12 can cause incoming air to exit the building before mixing with inside air, resulting in poor air mixing in the animal zone, and pockets of damp, stale, warm air.
It uses exhaust fans for its mechanically ventilated barns and is sized and placed according to barn structure and dimensions. Tunnel type ventilation can provide a rapid air exchange in connected barns in less than 45 seconds.
In naturally ventilated buildings, providing air exchange primarily depends on wind speed and direction. High-rise buildings without side and front walls are the preferred ‘summer mansion’ for cows to rest during the open summer months.
When the rate of hot air exchange in naturally ventilated buildings is challenged by topography, wind barriers or building limitations, provide necessary air exchange with well-designed tunnel or cross-ventilation systems.
Weather change
Fans increase the rate of heat sharing by constantly changing the air near hot systems and increasing molecular collision. The same is true for humans and animals. Since the number of molecules touching the skin of humans and animals increases rapidly, heat sharing also accelerates. The part up to about 5 cm from your skin is filled with high-temperature air. The fan also allows you to get rid of this hot air.
Turbulent air movement around cattle increases convective heat transfer and evaporation, minimizing “hot spots”. Air speeds of 3.5 to 5 miles (miles) 6-9 km per hour should be preferred in rest, feeding and holding areas.
Axial circulation fans with a diameter of 36 to 52 inches can provide excellent air movement for animal areas. The distance between the effective fans placed behind the back should be at most 10 times the diameter of the fan. In side-by-side applications, the fans should be separated from each other by 2-3 times their diameter.
Large, high-volume, low-speed (HVLS) fans can also provide air movement at low level, but should be placed above the animals and the distance between them should not be more than twice their diameter.
Fans are good vaporizers. You can observe this by experimenting. Wet two different paper napkins at the same rate and place one in a normal environment and the other in front of the fan. The one against the fan will dry faster. Just like the clothes dry faster when there is wind. Human skin is quite moist, and the humidity will increase in hot weather. The fan helps this moisture evaporate, allowing your body to cool down more quickly.
In fact, the last example is dangerous for humans. With this method, very rapid heat loss is experienced and can cause pain in the muscles. It can also cause sinusitis with its application in the head area. For this reason, it is recommended to be careful when using the fan.
Ventilation should focus on cows’ needs, not cost!
Drinking water
Increased breathing and urination in hot weather can increase drinking water intake by 20% or more. Irrigation stations need to be conveniently located, allow multiple cattle access, and keep up with water demand.
Animal and barn cooling systems
- Direct evaporative cooling (DEC) systems intermittently apply water to the animal skin by evaporating and drawing heat directly from the animal’s body.
- Indirect evaporative cooling (IEC), on the other hand, increases the rate of heat transfer by lowering the temperature of the ambient air surrounding the cow.
Animal cooling system
The air-cooling effect of natural and mechanical ventilation systems is limited. Heat stress can be reduced by directly cooling the animal by using it with MIST and/or HADAR animal cooling systems to reduce dairy cattle heat stress. This system is based on the principle of lowering the animal’s body temperature by wetting the animal’s skin with the Spray or Fog method, and then evaporating this wetness very quickly. Generally, it is applied in milking waiting areas and feeder table – feed road.
Evaporative Cooling:
Evaporative cooling uses water to increase heat transfer from cows. The evaporation of a pound (or pint) of water requires about 1,000 British thermal units (Btu) of energy, approximately the heat produced by 1,000 4” inch wooden matches.
Direct evaporative cooling (DEC) systems intermittently apply and evaporate water from the cow’s skin, drawing heat directly from her body. Indirect evaporative cooling (IEC) lowers the temperature of air surrounding the cow, increasing her heat transfer rate.
Spray cooling systems are low pressure DEC systems installed in feeding and holding areas that use a five to 15-minute wet-dry cycle. Spray nozzles emit a coarse droplet that penetrates the cow’s hair coat soaking her skin for one to three minutes. Fans provide air movement for the remainder of the cycle to speed evaporation and draw heat away from her body. Studies show the respiration rate of a heat stressed cow decreases with the first wet-dry cycle. DEC seems to be the most effective evaporative cooling method for cows in more humid climates like Pennsylvania. However, it can require a significant water supply and good drainage.
Indirect evaporative cooling (IEC) uses heat in the air to evaporate water, lowering the dry bulb air temperature. The heat transfer rate increases when the difference in temperature between the cow body and surrounding air is greater. Heat transfer from within the body also improves as cows inhale cooler air.
Since evaporative cooling systems involve adding water to the surrounding air of animals, ventilation systems and circulation fans that provide good air exchange are important to reduce the moisture load in the air.
Cooling systems with spray showering are low pressure DEC systems installed in supply and holding areas using a 5-to-15-minute wet-dry cycle.
The spray nozzles emit a coarse droplet that penetrates the cow’s bristle skin by soaking the cow for 1-3 minutes. Fans provide the necessary air movement to accelerate evaporation and remove heat from your body. Studies show that the respiratory rate of a heat-stressed cow decreases with the first wet-dry cycle. DEC seems to be the most effective cooling method for cows in humid climates. However, it may require a significant water supply and good drainage. LINK for products
Ambient cooling system
Indirect evaporative cooling (IEC) uses the heat in the air to take the moisture out of the air that evaporates from the heat and lower the air temperature. The heat transfer rate increases when the temperature difference between the animal body and the surrounding air becomes larger. As animals breathe cooler air, heat-transfer from inside the body increases.
Evaporative pads IEC is another method. Thick, water-soaked corrugated pads are placed at the entrance openings used with tunnel and cross-ventilation systems. Outside air drawn through the pad evaporates as much moisture as weather conditions permit, lowering the dry bulb temperature. All air drawn from the inlet is cooled and can only absorb as much moisture as weather conditions allow.
Fogging and misting are examples of IEC systems that force water by pressure through nozzles that emit very small droplets. High pressure systems emit droplets that have a better chance of evaporating onto the cow’s bristle skin surface before the floor. Low-pressure nozzles, on the other hand, emit larger droplets and are typically mounted on circulation fans, thereby aiding evaporation with air movement. Pressurized IEC systems are popular in arid climates where droplets are more likely to evaporate suspended in the air. These systems are preferred in naturally ventilated buildings.
Semi-Dry cooling systems
Semi-dry cooling systems, with high technology and sensitive nozzles, the water is divided into much finer and smaller pieces, and the light water hangs in the air (like fogging) without falling to the ground, and this water vapor is absorbed by the fan and the heat is absorbed down to -5 / -8 C degrees. ambient cooling.
Techniques used to combat dairy cow heat stress currently available include shade, adequate air exchange, good air movement, drinking water, and evaporative cooling. Used correctly, these tools can help balance daily heat gain and loss of dairy cows, minimize the effects of heat stress, and improve cow health, production and well-being during the summer season.
Barn Air Conditioning systems:
Systems that change and control air quality, humidity and temperature in addition to the ventilation system are called air conditioning systems and are suitable for fully closed barns. Cross and tunnel models are applied according to barn size and climatic conditions.
Fan selection is extremely important, as fan choice has the most impact on ventilation operating costs.
Ventilation should focus on cows’ needs, not cost!
Fan selection is extremely important, as fan choice has the most impact on ventilation operating costs.
A ventilation system for adult dairy cows must provide fresh air year-round and fastmoving air in the resting space to aid summertime cooling. This is true for both naturally and mechanically ventilated barns.
While 85 percent of free-stall facilities in Wisconsin are naturally ventilated, wind shadows (created by nearby buildings and seasonal cornfields), land availability, barn orientation, and other factors can limit the function of these systems. This has led to a growing interest in mechanical ventilation among dairy producers.
Mechanical ventilation
Mechanical ventilation relies completely on fans to provide an adequate ventilation rate and air speed in the cow’s resting area. for fighting dairy cattle heat stress. Mechanical systems are generally defined as tunnel (airflow parallel to the feed lane) or cross (airflow perpendicular to the feed lane) ventilation. However, there is little information on the cost of installing and operating these systems. Many producers have asked our team at The Dairyland Initiative for help deciding on a ventilation system for their facility. They often list cost (typically the initial investment) as one of their main concerns.
We modeled the capital and operating costs of seven ventilation systems and found that while cost is important, it should not be the main focus of the design. Each facility in our model was designed for 1,008 milking cows, and the systems were amortized over a 10-year period. The barns varied by ventilation system, fan or baffle placement, fan spacing over the stalls, and ventilation rate. The systems followed standard industry guidelines of summer ventilation rates (40 to 60 air changes per hour [ACH]), 4 ACH in the winter, and at around 500 feet per minute for the cross-sectional airspeed in the barn.
The study included:
Two naturally ventilated barns with fans installed on every support post (fans spaced 24 feet apart) or on every other support post (fans spaced — 48 feet apart). Two mechanically tunnel-ventilated barns; one was designed for 60 ACH with no fans over the stalls and another was designed for 40 ACH with fans over the stalls spaced 5 diameter-widths apart.
A hybrid ventilation system combining mechanical and natural elements, designed at 40 ACH with fans over the stalls, spaced 60 feet apart, and ridge cupula fans to assist with winter ventilation.
Two cross-ventilated barns designed with airflow at 492 feet per minute under the baffle for an eight-row barn and a 16-row barn.
The analysis included the natural variability of the weather by modeling the cost of running the fans at various temperature set points, winter to summer transition methodologies, and temperature profiles (average versus minimum or maximum daily temperatures). Similarly, we included the variability of fan performance based on publicly available testing data for exhaust and circulation fans.
Crunching the numbers
The total building costs ranged from $2,460 to $3,180 per stall. Hybrid ventilation was the most expensive to build because it used mechanical ventilation and had full curtain sidewalls.
In facilities built for 1,008 milking cows, the cost of running ventilation for naturally ventilated barns was $29,584 per year in Wisconsin, about half that of mechanical ventilation systems. There was very little difference in total cost between tunnel ventilation ($58,554 per year) and cross ventilation ($55,802 per year) in Wisconsin at this facility size.
Similarly, ventilation systems in more temperate climates (Wisconsin, Washington, and Minnesota) cost about half as much to operate as those located in hotter climates (Arizona and Florida). This is mainly because the number of days the average daily temperature is above 68°F — at which the ventilation system operates at max capacity — is about double in hotter areas.
The right fan for the job
A natural ventilation system using poor-quality circulation fans can cost the same to operate as a mechanical ventilation system using high-efficiency fans. Fan selection had the highest impact on the operating costs for all ventilation systems.
We were surprised to see how much variance existed in fan performance and the relative importance of selecting an efficient fan. High-efficiency fans tend to be more expensive, but the investment is easily paid back by the lower operating costs over time.
Of the total cost of installing and operating a ventilation system for 10 years, on average, 24 percent of the total cost was the capital investment and the remainder was operating cost. Some high-efficiency fans also qualify for rebates from programs that were not part of the study and would further reduce the capital cost.
When selecting fans for ventilation systems, it is important to check the fan’s ventilation efficiency rating (VER), which is listed as CFM (cubic feet per minute) per watt. Untested fans can have ratings 50 percent less than what a manufacturer advertises, so it is important to find fans that have been independently tested.
The two most common testing facilities available in the U.S. are through the Air Movement and Control Association (AMCA) and the Bioenvironmental and Structural Systems (BESS) Laboratory at the University of Illinois. AMCA also has a certified product rating, and these products will bear an AMCA sticker stating what specific value was rated and certified.
Regardless of what fan is installed, agricultural fans are exposed to humid and dirty environments. Poorly maintained fans can lose 30 to 50 percent of their efficiency, and our experience suggests that fans are not well maintained on many farms.
One limitation of this analysis is that all fans were single-speed fans. Most ventilation companies now offer a variable speed drive (VFD) fan that is automatically controlled by temperature-sensing technologies.
In one of our previous studies for a cross-ventilated barn using VFD fans, fine-tuning the transition between summer and winter could, in theory, reduce operating costs by $6 per stall per year. This would be 10 to 25 percent of the ventilation operating costs.
If a ventilation and cooling system provides the recommended air speed in the resting space occupied by the cow and fresh air throughout the year, it will always be a sound investment. When deciding between different types of ventilation systems for a new facility, other factors like day-to-day management, fan maintenance and number of fans, barn orientation, footprint per stall, cow flow, manure handling, or personal preference should outweigh the cost of the system, provided the right fan choice is made.
Based on our experience and results from these cost estimations, we believe that using the most efficient fan for each system, and following a proper maintenance protocol, surpass other energy-saving methodologies related to ventilation and fighting dairy cattle heat stress.
