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Keep Your Dry Cows Cool During the Summer Months
Pennsylvania Ag Connection - 05/31/2023

Managing heat stress is a common challenge for dairy farms worldwide.

As we know, dairy cows do much better in colder and drier environments than in warm, wet conditions.

Heat stress happens when the animal is not able to regulate its body temperature due to high outside temperature and humidity conditions.

When this occurs, the animal is not able to decrease its body temperature to maintain it in the normal range, and the body overheats.

Depending on the degree of overheating, this event can have mild to severe consequences to the animal’s health and performance, including death in severe cases.

The milder signs observed when animals are heat stressed are panting, decreased appetite, decreased milk production, and decreased fertility. Furthermore, animals can be lethargic and found lying in wet, shady areas or crowding around the water sources.

It has been estimated that heat stress costs the U.S. dairy industry more than $1.5 billion annually. The main losses are related to lower milk production and reproductive performance.

Incidence of heat stress varies depending on region, tending to be higher in the Southern states. In Pennsylvania, dairy cows are usually at the highest risk between June and August.

The most accurate method to monitor heat stress is by assessing the temperature humidity index, instead of solely monitoring environmental temperature.

There are different degrees of heat stress in cattle, but as a rule of thumb cooling devices should start working when the index is above 68-70 degrees.

Fans, soakers and misters located in key areas in the barn — such as the holding area and feed alley — along with proper barn design to achieve good ventilation and air flow are some of the key components of a proper heat abatement program.

While the farm may have all or most of these components in place, the management of them is what makes the difference between cool cows and heat-stressed cows.

Other aspects of the overall farm management, such as avoiding overcrowding and providing sufficient fresh clean water (3 inches of water surface per animal), are just as important.

Behind the well-known drop in milk yield and decrease in reproductive performance in lactating cows, heat stress has long-lasting effects in dairy cows, especially in dry cows and their daughters.

Although more attention is being placed on this often-forgotten group of animals, it is not uncommon to neglect heat abatement management for this group due to the upfront cost of these practices and the incorrect perception that these animals may not need much special management since they are not being milked.

Heat stress can affect the performance of dry cows in their subsequent lactation, even if they are not heat stressed during the lactation period. It has been reported that cows that experience heat stress in the late gestation period produced about 8 pounds less milk per day (10.3% decrease) compared to non-heat-stressed dry cows.

Exposing dry cows to heat stress not only affects the dam’s performance but also hurts the performance of their daughters.

On average, these heifers are 12.4% lighter at birth and 10.4% lighter at weaning compared to calves born to non-heat-stressed cows.

In addition, these heifers will produce about 11 pounds less milk per day up to their third lactation, even if they have proper heat abatement management during their postnatal life.


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