Plan ahead to ensure you're ready to handle heat stress in the summer months

It makes sense to plan ahead and be ready for the next warm season. Dr. Geoffrey Dahl, animal sciences professor at the University of Florida has researched the impact of heat stress on dairy herds.

Lactating cows exposed to high temperatures and humidity usually eat less and produce less milk. The severity and duration of the heat stress, coupled with or without nighttime cooling, will dictate the impact on milk production and extent of recovery once the temperature drops. However, are the non-lactating animals in the barn affected by thermal stress? Simply put, the answer is yes and to a greater extent than you might think.

During the dry period, the mammary system undergoes many changes. Tissues grow and extensive cell turnover takes place. This process compensates for the cell loss that took place during the previous lactation. The extent of the regeneration process dictates the number of milk-producing cells and their production capacity. Environmental factors, such as photoperiod and temperature, have been shown to affect subsequent lactation.

For example, cows exposed to a short-day photoperiod during the dry period produce more milk and have improved immune function than other cows dried off under a long-day photoperiod.

Temperature and humidity are other important environmental factors. Dairy cows prefer cool temperatures. As the temperature gets warmer, especially if the relative humidity is high, heat stress signs may present, such as lower dry matter intake and reduced milk production for lactating animals. Dry cows can be negatively affected by warm temperatures. Further, the effects of heat stress may extend well into the following lactation. University of Florida researchers in Gainesville found heat stress during the dry period compromises mammary development. This decreases milk production in the following lactation even if the stressor is no longer present.

The dairy cow dry period is critical in many ways. Conditions that prevail during those two months will influence the outcome of the subsequent lactation and the offspring and its performance. Maternal heat stress during late gestation can reduce the gestation period. The fetus grows at a rapid rate during the last two months of gestation. Premature birth decreases the newborn calf's weight, including its weight at weaning and puberty. Passive immunity from the colostrum can be compromised in calves from heat stressed dams because immunoglobulins transferred from the colostrum to circulating blood are lower.

Offspring from cows exposed to heat stress during the dry period will tend to have poorer reproductive performance and decreased milk yield, at least during the first lactation.

The impact of the environment on dry cow health and future productivity is more significant than previously thought. The effect on offspring can be quite significant. These findings emphasize the importance of heat stress abatement for lactating animals and dry cows. There are several ways to mitigate the effects of warmer temperatures during the summer months. Providing plenty of drinking water and making it easily available for dry cows is an excellent first step. Access to shade, good ventilation and air movement are other simple means to reduce heat's impact on your herd. Now is the time to consider whether you will need to make changes to your barn to ensure your cows are comfortable when summer returns.

One more step that can be used to reduce the effects of heat on animals is to cool them with water. Sprinkler or misting systems are fairly common in large herds in New Zealand and the United States. Most of the time, sprinkler systems are associated with fans. The cooling effect of the water is enhanced by the evaporation induced by the fans. These systems are usually installed where cows congregate or above them at the feed bunk.

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Author: Mario Mongeon - Livestock Specialist/OMAFRA
Creation Date: December 2015
Last Reviewed: December 2015