Heat stress not only reduces milk production, it causes physiological changes with impacts that can remain long after the actual heat event has passed, such as aborted pregnancies and maternal death, not to mention declines in milk productivity that may never be regained.
Fans, shade coverings and even sprinkler misting systems in use today will not be able to counteract the effects of frequent or intense heat stress events, particularly in high humidity conditions. Energy and water consumption concerns, in turn, make these methods expensive and impractical for many.
One new method of reducing heat stress is being studied at Cornell University by Kristen Perano, a doctorate student in the department of biological and environmental engineering. Her studies experimenting with conductive cooling were published in the Journal of Dairy Science in August.
Perano presented her findings at the recent Dairy Environmental Systems and Climate Adaptation Conference, held at the university in July.
The objective of Perano’s research was to “test the effectiveness of conductive cooling in alleviating heat stress in lactating dairy cows.” Eight first-lactation Holstein cows were used in the study. The cows had similar milk production numbers and were in milk for roughly 166 days.
They were milked twice daily. Rectal temperature, dry matter intake (DMI) and milk production were measured twice per day. Respiration rate was measured five times daily.
Physiologically, increased respiration rates and an increase in rectal temperatures indicate the cow is heat-stressed. As a result, milk production decreases and less time is spent lying down. Higher-producing cows show a larger drop in productivity than lower-producing cows under the same conditions.
During a seven-week period, four cows were kept as controls, exposed to the stress but not cooled via conductive cooling or any other method. The other four were also exposed to heat stress but were cooled via conductive cooling.
All cows in the study were given Dual Chamber Cow Waterbeds from Advanced Comfort Technologies, which were placed on insulation and plywood over the concrete floor.
The conductively cooled beds were modified to allow water to continuously flow through the bed. The control beds were filled with water per the manufacturer’s guidelines. The modified beds were pressurized to maintain pressure and volume comparable to the non-cooled waterbed with a cow lying on it. A light layer of sawdust was used for bedding.
For the first week none of the cows in either group were exposed to heat stress, and baseline data was gathered. In the weeks that followed, half of the cows were exposed to a heat-stressed environment with the temperature-humidity index (THI) averaging either 80 or 79.
The water used for conductive cooling was also trialed at two temperatures: 50ºF and 40ºF; thus, a total of four conductive cooling treatments were tested.
Control cows and heat-stressed cows were kept in identical tiestalls and released into night pens for exercise where there was no exposure to heat stress. The cows in the study were fed free-choice wet TMR, had free access to water and were provided with free-choice timothy hay in the night pen.
All cows faced the same direction in the stalls and were kept in the study environment for 12 hours per day, just prior to morning milking until the evening milking.
During week six, the control cows became study cows, and the previously heat-stressed cows became the controls. For this week, the cows were exposed to the lower-heat-stress environment, with a 79 THI, and the cooling water temperature of 40ºF was used.
In week seven, waterbeds were used without any conductive cooling and placed directly on concrete to see if any noticeable cooling occurred from heat exchange with the concrete alone.
Impact of conductive cooling
Perano’s research revealed that conductive cooling effectively mitigated heat stress in lactating dairy cows. When cows were conductively cooled with 40ºF water, rectal temperature decreased, respiration rate decreased by 18 breaths per minute, milk yield increased by 5 percent and DMI increased by 14 percent compared with the control cows.
Rectal temperature was slightly lower when cows were cooled with colder circulating water, but other variables did not show a significant difference between cooling water temperatures.
Waterbeds placed directly on concrete, with no insulating layer, had no detectable impact on heat stress. This indicates that the cooler temperatures found in concrete alone cannot generate a conductive cooling effect.
In the Northeast, the benefits of conductive cooling need to be weighed against the energy needed to cool the water.
Perano noted that this region may not have enough heat stress to justify the use of a conductive cooling system, and the feasibility of conductive cooling will require more complete economic analysis.
The primary goal of the study was to determine if conductive cooling systems could alleviate heat stress in lactating dairy cows. The overall results of the study were clear. Conductive cooling, using water circulating through waterbeds, did mitigate the impacts of heat stress.
“The conductive cooling we were seeing was because we were actively cooling the water,” Perano said. PD
Tamara Scully, a freelance writer based in northwestern New Jersey, specializes in agricultural and food system topics.
Beyond Print: Progressive Dairyman first wrote about the concept of conductive cooling in March of 2014. Read more about it here: Can biogas-to-electricity waste heat be captured to help cool cows?