High temperatures have adverse repercussions on herd health and productivity. Proper management and nutrition strategies are used to minimize the impact of heat stress in dairy cattle, reducing the associated economic losses.

Temperature and humidity are critical to maintain cow comfort. The ideal temperature zone for dairy cows is approximately 50 to 750F. Above 80 to 900F, and especially over 20 percent relative humidity, dairy cows can start demonstrating signs associated with heat stress. A decrease in dry matter intake (DMI) (about 8 to 12 percent) followed by a reduction in milk production (3 to 20 percent) are typically present and suggest an increased risk for associated metabolic disorders.

Animal signs
As weather conditions become more challenging, prevention as well as continuous observation is key to assure minimum disruption in productivity.

Seeking shade, presenting lethargic appearance and higher respiration rate are usually easy, detectable signs as the cows fight to decrease internal heat.

Less notable signs are a raise in heart rate and body temperature, higher saliva production and profuse sweating.

Longer term effects such as reduced fertility and conception rates are usually compromised. Low activity during estrus, reduced follicular activity and high embryonic death are due to a redistribution of the blood flow to peripheral organs, compromising the level of hormones and nutrients for reproduction.

Special attention needs to be given to early lactation cows, which are typically more prone to be affected due to the negative energy balance and immune system depression as well as a high export of nutrients through milk.

Managing heat stress with nutrition management
It’s important to understand nutrient requirements for dairy cattle under heat stress conditions are not dramatically different. Proper adjustments in the diet should be considered with the purpose of balancing nutrient supply, due to the decrease in DMI, and loss of specific minerals through increased sweating and urination.

Water quality and availability are critical as consumption can increase 4 to 6 gallons per cow per day as temperature rises. Water should be provided immediately after milking and made available in several shaded locations (travel lanes and freestalls). Cleaning and monitoring water troughs on a regular basis encourages water consumption.

Feeding frequency, time of feeding and adequate feedbunk space should be optimized. In periods where DMI is depressed, the rumen ecosystem is disrupted and microbial growth (VFA production) is compromised, negatively impacting milk yield.

Ration modification can reduce the effects of heat stress on production but should be carefully monitored through a professional nutritionist’s recommendation.

A higher grain-to-forage ratio can lead to metabolic problems, such as acidosis. Using high-quality forages and effective fiber are key to promote nutrient availability and stimulate rumination, which supports rumen pH stabilization. Sorting should be minimized through proper total mixed ration (TMR) mixing.

The use of protected fat increases the diet density as an alternative to non-structural carbohydrates and protein as sources of energy. Recommended levels should never exceed 7 to 8 percent total fat in the total diet.

In order to maintain a good balance between palatability and proper dry matter, providing 60 to 70 percent of the feed in early and evening hours is advisable and a higher number of feedings per day would reduce bunk and feed spoilage.

Silage and bunk management are important. Silage should be removed as close as possible from feeding to compensate the shorter bunk life and potential secondary fermentation during hot weather. Mold inhibitors and mycotoxin binders are recommended to reduce the impact of related pathologies.

Specific mineral requirements, such as potassium, sodium and magnesium, increase due to export in sweating and urination.

Several feed additives, such as live yeast cultures, buffers, fat- soluble vitamins (A, D and E), niacin and selenium, can be considered to improve rumen function, immune response, promote energy utilization and feed conversion efficiency.

Cooling systems
Strategies to cool dairy cows are diverse and are dependent upon the structures and equipment available as well as how aggressive the producer needs to address each application.

The focus should be primarily on the parlor holding pen and the feeding aisle to promote cow comfort and encourage feed consumption. Most recommended systems use a combination of water and air movement to promote evaporative cooling.

Using shower head nozzles as the cows exit the parlor is a cheap and effective way to cool cows and encourage DMI as they get to the feed.

Establishing the right timing for the sprinkler system requires evaluation. Reducing the time of exposure as the water drips from the udders is advisable as there is a higher risk of developing new cases of mastitis.

Providing shade as well as air movement through a good ventilation system in conjunction with a controlled sprinkler system installed in the feed aisle contributes to cow comfort and encourages feed intake, with positive repercussions in productivity and herd health.

Summary
Reducing the impact of heat stress in dairy cows is crucial to maintain productivity and efficiency on the dairy.

Water availability and quality as well as an effective cooling system promote cow comfort, encouraging feed intake and reduction in metabolic problems.

The ration should be properly balanced, well-mixed and accessible throughout the day. Effective fiber promotes rumination and optimized rumen function.

Monitoring the symptoms presented by the cows is critical to act sensibly in preventing losses in productivity and reduce the economic impact of health problems related to heat stress. PD