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1008 PD: Feeding a top performer to beat the summertime heat

Elliot Block Published on 30 June 2008

Dairy cows perform much like world-class athletes, exerting high levels of energy for daily maintenance and to maintain high levels of production, says Dr. Joe West, University of Georgia dairy scientist.

The higher the milk production, the more energy digested, and as a result, the more heat released. Compound this with the effects of hot, humid weather and you’ll find top performers need the best environment and the right diet to mitigate the heat’s negative effects.



As many producers have experienced, heat stress leads to a decline in dry matter intake (DMI) and milk and component production. What producers may not recognize, warns West, is the multiple health problems that can result simultaneously from heat stress. Hoof problems, rumen health disorders and poor reproductive performance have also been linked to heat stress, and these problems can be compounded by overstocking and poor ventilation.

Amp up the ration
To adjust for lower DMI, West stresses the importance of getting the most from each bite of feed. He recommends boosting energy, protein and minerals to meet the herd’s nutritional needs.

Energy is critical during heat stress because more energy is needed for daily maintenance and production. But it’s not as easy as just adding more corn. Diets high in fermentable carbohydrates, like corn, can cause rumen acidosis, a health disorder cows are more prone to during hot weather. West recommends adding other high-energy sources to the ration, like bypass fat or cottonseed, to meet the energy demand while also maintaining rumen integrity.

West notes the importance of feeding a high-quality fiber source to stimulate rumination and maintain rumen health. Higher-quality forages are especially important in hot, humid conditions because low-quality feedstuffs take more energy to digest, resulting in greater heat production. Couple the additional heat output to an already hot external environment, and it’s easy to understand why DMI and performance can decline.

Key minerals during heat stress
West also recommends higher levels of alkaline minerals, especially potassium and sodium, which raise ration dietary cation-anion difference (DCAD) to help buffer the rumen, maintain DMI and mitigate many of the other negative effects of heat stress.


When cows are heat-stressed, they lose potassium more quickly through increased perspiration and urination. Potassium is critical for the cow’s body because it serves as the primary regulator of sweat gland secretions, along with a plethora of other body functions, including milk production and cow cooling.

By adding a high-quality potassium carbonate to the ration, cows can transition better during the summer heat, maintain DMI and experience more consistent herd health and performance. West recommends DCAD levels in the range of +35 to +45 milliequivalent (meq) per 100 grams ration dry matter during heat-stress conditions. Potassium levels should be 1.5 to 1.8 percent of DMI during extreme weather. These levels are necessary, he adds, to maintain herd productivity and herd health while temperatures are on the rise.

Feeding habits
Cows can change their eating habits during extremely hot conditions, so it’s important to focus on what the cow needs, rather than relying on a set ration formulation and delivery schedule, says West. He says managers must adapt to the cow’s needs by understanding when and what she requires to survive the hot conditions.

Slug feeding. When cows eat large meals during the day, there are peaks in heat output from digestion as well as high levels of acid in the rumen. West recommends feeding cows smaller meals throughout the day to maintain buffering and control acid levels in the rumen, which may reduce high heat output during digestion.

Eating in cooler weather. West says it is helpful for cows to experience their highest heat output from rumen fermentation before the hottest times of the day. For example, most locations plagued by heat stress see the coolest temperatures around 5 a.m. Cows should be fed as close to this time as possible, as they will consume more dry matter, and rumen fermentation will peak around 9 a.m., or approximately four hours after feeding, far before the hottest part of the day.

Provide a cool ration. If the ration heats up with secondary fermentation, feeds can change palatability and composition. Cows are already slowing DMI, so keeping feed integrity intact and promoting intake will prove beneficial. Shades over the feedbunk keep the ration cool and appetizing.


Increase water needs. Cows need large volumes of clean water to keep cool during the hot summer months. Each pen should have ample waterers and appropriate water flow rates to ensure every cow has enough water to meet its increased daily needs. Ensure waterers are clean and free of debris.

Managing the environment
West notes the small details can make all the difference when it comes to managing the environment in hot weather. It’s critical to provide just the right surroundings to complement the properly formulated ration.

Avoid direct sunlight. This only makes a hot environment even more uncomfortable. Provide shades to avoid direct contact, which can be especially brutal during the afternoons.

Air movement. Cows sweat during heat stress, which makes air flow critical. West notes many producers are using tunnel-ventilation systems to keep temperatures comfortable in the barn. If this is not ideal for your operation, utilize natural air flow and fans to provide adequate air movement.

Water for cooling. Misters and soakers alongside fans result in evaporative cooling, which helps evaporate moisture from the cow’s body and cools her.

Parlor setup. Once a cool environment is created in the barn, moving cows to and from the parlor must be addressed. The long walk to and from the parlor could result in additional heat and stress. West suggests finding any way possible to avoid long bouts away from the cooler environment in the barn. When cows are waiting in the holding pen to be milked, use fans, sprinklers and misters to control the temperature.

As you prepare to combat summer heat, here are the three main areas of focus to keep cows healthy and performing to their potential, all while fighting the summertime temperatures:

– Provide more energy and adequate potassium levels in the ration to meet the herd’s increasing nutritional needs.

– Feed cows how and when they are most apt to eat, which will most likely be smaller meals during cooler parts of the day.

– Do everything in your power to keep cows cool, whether it’s using fans, soakers, sprinklers or natural ventilation. Any way you can keep cows cool will allow for more energy utilized for milk production and reproductive function. PD

References omitted but are available upon request at

Elliot Block
Animal Nutrition