Seven practical heat stress abatement strategies
Minimize heat stress in your dairy cows by following these strategies.
All dairy producers are aware their cows are subject to heat stress on warm summer days. Experts estimate heat stress causes $5-6 billion in lost milk production and decreased animal performance in the U.S. each year. Dairy cows are more sensitive to heat stress than many other mammals because of the high metabolic heat production due to fermentation in the rumen. Dairy cows experiencing heat stress show higher rectal temperatures, increased respiration rates, decreased feed intake, decreased milk production (volume and components), and other health problems (e.g., decreased reproductive efficiency). Very importantly, as dairy cows produce increasing amounts of milk the heat production from the rumen increases and makes them even more susceptible to the harmful effects of heat stress.
Practical and successful heat stress abatement strategies are based on the modes of heat exchange between cows and their surrounding environment:
- Conduction: heat is transferred from a warm substance to a cooler substance without the substances moving. Example: heat loss from the cow to the air or floor.
- Convection: heat is transferred from a warm substance to a cooler substance where the substances are moving past one another. Example: air movement over the cow’s body.
- Radiation: electromagnetic radiation is absorbed at the surface of an object. Example: the radiant energy exchange from sunlight to the cow or from the cow to the night sky.
- Evaporation: heat is exchanged by converting water from a liquid to a gas. Examples: sweating, sprinkling water on cows and breathing.
Here aredairy producers can use on their cows:
- Shade: Shade reduces heat stress by
decreasing exposure to solar radiation. In Michigan most cows are housed in free stall
barns. Ideally freestall dairy
be oriented east to west
to provide maximum shade under
the roof. Barn roofs should be white
colored galvanized metal or aluminum to provide maximum reflection of solar
radiation. During times of extreme heat
stress (high temperatures, high humidity) nighttime temperatures do not provide
adequate relief from heat stress. During such times, if
possible, allow cows access to pasture at night. Cows are able to dissipate
more heat via radiation to a night sky than to a freestall barn. This strategy is even more
important for very high producing cows under greatest heat stress. If shade is offered in a
pasture environment, be sure to manage it properly to avoid creating a mud hole
which is detrimental to health (e.g., increased mastitis).
Ventilation: Proper ventilation is critical to maximize convective heat loss from cows. A good ventilation system should provide one complete air exchange per minute. This is usually accomplished using fans. Each fan should provide airflow of at least 11,000 cfm. Fans of this size will move air effectively for about 10 diameters. Therefore, a 30 inch fan is effective to about 30 feet, a 40 inch fan to about 40 feet. Fans should be mounted at an angle to blow over the backs of the cows as they lay in the free stalls. It is also important to take advantage of natural ventilation in free stall barns. To provide maximum natural ventilation sidewalls should be open and open ridge vents are optimal (minimum of one foot wide, plus two additional inches per ten feet of building width). Ridge caps are usually not a problem if they are at least one foot above the ridge opening. Overshot ridge openings should be avoided because they greatly limit fee air flow. Attention should also be paid to eave height. For buildings up to 40 feet wide, a 12 foot eave height is adequate. For buildings over 40 feet wide provide at least 14 feet. Heat stress is even higher in the milking parlor holding pen; therefore, this area should also have adequate coverage with fans. During times of greatest heat stress decreasing group size in the holding pen should be considered.
Drinking water: Heat stress greatly increases water intake in cows. For example, increasing air temperature from 86 degrees F to 95 F increases water intake in lactating dairy cows by over 50 percent (about 21 gal/day to about 32 gal/day). Therefore, it is critical to offer plenty of fresh clean drinking water. Water trough management in times of heat stress should be more intense and more frequent to insure water is clean and free of algae. Ideally cows should not have to walk more than 50 feet to get water and not have to walk through, or stand in, direct sunlight to drink. It is also a good idea to provide fresh, clean water in the exit area of the parlor. Water consumption is usually highest right after milking. As a rule of thumb, provide two inches of linear water trough space per cow.
cooling: Supplemental cooling using
sprinklers is another strategy, especially effective for high producing cows. Sprinklers can either lower
air temperatures directly through misting and fogging, or provide “artificial
sweat” by soaking the cow’s skin. The latter is most advisable
since misting and fogging systems are more expensive to install, operate and
maintain; plus they may create respiratory health problems. Sprinkling with wetting to
the skin is also much more effective when combined with fans.
routine: Heat stress is highest when
temperatures are highest. Feeding at this time of day
results in poorest dry matter intake and increases the rate of feed heating and
spoilage. Therefore, consider slowly
shifting your feeding schedule, especially for high producing cows, to the
cooler portions of the day (i.e., early morning and/or late evening). Also, increase the frequency
of pushing up and removing spoiled feed to promote higher dry matter intake.
formulation: Heat stress results in
depressed dry matter intake. In times of severe heat
stress reformulate the ration to increase its energy density without increasing
the heat of fermentation. This is usually accomplished
by adding rumen inert fat. Adding increased bypass protein
is also an important consideration due to the decline in dry matter intake and
rumen heat production. The ration potassium level
should also be adjusted upward since potassium loss is high due to increased
sweating. When considering any ration
change it is absolutely essential to consult a qualified dairy nutritionist.
- Stocking density: Most dairies routinely overstock their free stall barns. In times of high heat stress overstocking makes heat stress worse. Therefore, consider reducing stocking densities to 100 percent and provide 30 inches of feed bunk space per cow to encourage dry matter intake.
Heat stress abatement is a critical dairy management strategy for all dairy producers. Properly applied, these seven heat stress abatement strategies can minimize the harmful effects of heat stress on dry matter intake, milk production (volume and components) and reproduction. Be sure to include every animal on your dairy when considering heat stress abatement strategies. Heat stress affects not only high producing milk cows, but also dry cows, heifers and calves.
Related Michigan State University (MSU) Extension News article: Heat stress affects heifers and growth rate.