Economic impacts of heat stress
Each year we complain about summer heat as if we are surprised by it, but the truth is Minnesota's average high temperatures hover around 80°F. As temperatures near 80°F people may only feel mild discomfort, but our cows are affected much sooner. As Jeff Reneau explains in the companion article, cows can be stressed at temperatures as low as 72°F, or when the temperature humidity index (THI) reaches 68. In order to minimize economic losses caused by heat stress, it is important to be proactive with heat abatement strategies.
Where does heat stress impact your pocket book?
Profitable dairies strive to maximize milk production. However, as milk production and dry matter intake increase so does a cow's metabolic heat output, which increases sensitivity to heat stress (Collier, University of Arizona, 2012). The three main heat stress symptoms driving economic loss are:
- Decreased dry matter intake. Dairy cattle will significantly decrease dry matter intake during heat stress in an attempt to reduce heat production from the digestion and metabolism of nutrients. It is important to develop a nutrient dense ration during periods of heat stress (see "Nutrition Adjustments for Heat Stressed Dairy Cows" by Litherland and Sawall in the July 14th issue of Dairy Star, or look for it on the University of Minnesota Dairy Extension website).
- Low milk production. Milk production can be significantly reduced during heat stress. A recent paper titled "Quantifying Heat Stress and Its Impact on Metabolism and Performance" indicated that when cows experience days where the THI is between 65 and 73, milk yield loss averages 5 pounds per cow per day. According to this projection, during a summer in which the THI reaches these levels for 30 days, lost milk income from a 150-cow herd can add up to as much as $3375 per year (based on $15.00 per cwt).
- Impaired reproduction. Heat stress hinders reproductive performance of the dairy cow and consequential impacts can be seen for months following the exposure. Decreased fertility can lead to more days open and disrupt the cycle to which a cow enters and exits the milking herd. In addition, embryo loss is 3.7 times more likely in times of heat stress (Thatcher et al., 1986). A single cow's pregnancy is worth an average of $450 (Fricke et al., 2010); however, this value can vary based on a cow's age, future production potential and days-in-milk.
Is heat abatement worth it?
As explained above, heat stress can take an economic toll on several areas of the dairy operation. However, given the small number of days that Minnesota experiences high temperatures, is the investment worth it to incorporate heat abatement systems for the dairy herd?
A study completed by Norm St-Pierre (Ohio State University, 2003) evaluated the annual economic impact of heat stress on dairy cows and found that without heat abatement strategies in place, the nation's dairy industry incurred an economic loss of $1507 million. At a Minnesota level, in a year when 34 days exceed the THI threshold, 520,000 dairy cows tally an economic loss of over $27.7 million even with optimal heat abatement strategies. As we apply those numbers to a 150-cow herd, we realize that in an average year Minnesota heat stress contributes to $53.00 in lost income per cow and robs a dairy operation of $7950.
It is important to realize that heat stress can carry more severe penalties depending on the physical location of a herd and its environmental surroundings. Nevertheless, some form of heat abatement is economically justified.
Creating a heat stress management plan:
Keeping the negative economic impact in mind, it is important to be proactive in alleviating heat stress to minimize financial losses. With a number of heat abatement strategies available, developing a heat stress management plan that is both affordable and effective can help keep dairy herds comfortable and with money in their pockets. Consider the following when developing a heat stress management plan:
- Adequate air movement. Increasing air movement is an important component to reduce heat stress. Two simple ways to create air movement throughout the barn include adding fans and opening the sides of the barn, and installing nets or curtains.
- Availability of water. As the temperatures approach heat stress levels, adding extra water sources is a must. Cows will increase water consumption in heat stress conditions and crowding can occur. Also consider adding sprinklers.
- Ample shade. If your herd is kept outside during the summer months, it is essential that you provide shade for them to get out of direct sunlight. If no trees or other natural sources of shade are available, consider adding a netted area as an alternative. Shade over the feeding area will keep cows cool and help with dry matter intake.