These days, whenever you read or discuss an article about dairy cows, the issue of cow comfort is sure to come up.

As a term, cow comfort has gained acceptance at face value with a defined meaning of its own. However, the definition can be elusive when talking about a precise issue. It seems as if cow comfort is becoming a diagnosis or catch-all category to explain issues or problems on a dairy that are not easily solved by usual attempts.

Cow comfort can be defined as: Any cow-perceived situation that induces a negative reaction or response leading to a less-than-ideal condition for the cow, inhibiting her genetic potential and ability for maximum dairy production.

A long list of specific cow comfort issues can be created from these five general areas:

• Cow-to-cow interactions

• Facility

• Environment

• Health

• People interaction with cows

Cow comfort is more than a descriptive term; it’s a condition which affects both cow health and your dairy’s bottom line. To understand this point, let’s examine one of the environmental categories of cow comfort – heat stress.

How heat affects health
In most regions of the U.S., summer is at its peak. In both the temperate and southern parts of the country, summer brings heat stress and its negative impact on dairy cattle performance. To best manage the effects of heat stress in the dairy environment, preparation should start before seasonal heat and humidity arrives.

Heat stress defines a condition that has multiple factors. It occurs when a cow’s heat dissipation is exceeded by her heat load exposure from high environmental temperature, humidity and maintenance/production requirements. The recognized clinical signs are:

• Increased respiration rate (panting)

• Sweating

• Reduced dry matter intake

• Reduced production

• General inactivity attributed to imbalances in energy, fluid and electrolyte metabolism

This imbalance develops primarily from a shift in energy metabolism and also from circulatory adjustments for water and salt losses induced by evaporation from sweating and panting.

Heat-stressed cows become more insulin-sensitive, resulting in decreased use of body fatty acids as a source of energy and increased use of glucose by cells as the preferred energy source. By doing this, the cow will generate less accumulated internal metabolic heat. This is a protective mechanism to reduce the metabolic heat load.

Lactose production is the primary determinant of milk yield. Increased metabolic use of glucose during heat stress means less glucose available to the mammary gland for milk lactose synthesis. This is one of the major causes of decreased milk production in periods of sustained heat stress.

The net effect of all these heat stress biochemical changes is a change in the cow’s energy metabolism, potassium depletion, sodium depletion, metabolic acid-base alterations, reduction in phosphorus and ionized calcium, pulmonary edema and tissue dehydration.

The effects of heat stress on your overall dairy operation are lost pounds of milk, lower milk components, poorer breeding/fertility, compromised immune system, increased fresh cow metabolic problems and hoof/laminitis problems. How you manage heat stress determines the magnitude of these effects, both short- and long-term.

Taking the heat off your cows
There are four ways a cow can cool herself: conduction, convection, radiation and evaporation. The first three require a difference in temperature between the cow and her environment; a thermal gradient and evaporation that works on a vapor pressure gradient. Conduction occurs when a cow lies on a wet surface. Convection is when air moves past the skin’s surface. Radiation losses occur at night if the air cools. The fourth way, evaporation – sweating or panting – is what a cow relies on to lose the most heat.

Providing your cows with environmental relief from heat requires shade (45 to 50 square feet per animal), water misters set on timers to wet the backs of cows to the skin and then allow for drying and fans that move the surrounding air at 2 to 5 miles per hour.

Reduced milk production is also associated with decreased dry matter intake (DMI), reduced blood flow to the mammary gland and other factors. DMI can decrease up to 55 percent during severe heat stress compared to cows in a thermal neutral zone of 40 to 70°F. As DMI goes down, the cow’s nutrient requirements actually increase due to the physical efforts of cooling. It has been estimated that heat-stressed cows can be in a negative energy balance of 4 to 6 Mcal per day.

A cow affected by a moderate-to-high heat index will resort to open-mouth panting and drooling. In this state, she has used up her cooling capacity reserve. Respiratory rates are over 80 per minute, respiratory alkalosis is setting in and metabolic acidosis will alter her body chemistry. At this point, how you relieve her heat stress makes the difference between disaster and a manageable situation.

Nutrients for heat stress management
When the temperature soars, water can become a limiting nutrient. A cow will drink up to 30 to 50 percent more water at 80°F than at 40°F. However, water consumption can decrease when the temperature is over 90°F due to inactivity and decreased DMI. In hot conditions, a cow’s water intake is first used to manage her heat stress – what’s left goes into milk production. Therefore, unrestricted access to quality water is critically important.

Diet is your second management tool for assisting heat-stressed or potentially heat-stressed dairy cows. Forage quality must be maintained and nonfiber carbohydrates should be less than 40 percent, NDF at 30 percent and ADF at 20 percent; a minimum of 21 percent forage NDF is necessary to avoid rumen acidosis. Fat can be increased to maintain energy. Protein should support the level of milk production, but don’t feed a lot of degradable or soluble protein. Degradable protein should be kept at about 60 percent.

Bunk life is more critical in the summertime. Consider using a stabilizer feed product to preserve and reduce heating of the TMR. Reduced stress during times of high environmental temperature and/or humidity can be achieved by feeding during the cool times of the day and feeding twice a day rather than once. Buffers should be added to the diet from 0.8 to 1.5 percent.

Studies at Florida State as far back as 1987 found that adding electrolyte ions to the diet improved feed intake and water consumption. Current trials have expanded upon these studies and support the need for supplementation. When a cow sweats, potassium is lost, and sodium is excreted to compensate for the potassium reduction. Therefore, you should increase potassium in the diet to at least 1.5 to 1.8 percent, and increase sodium to 0.4 to 0.6 percent. Magnesium, because of the higher potassium levels, needs to be between 0.35 to 0.40 percent, and chloride should be 0.3 percent. It is recommended this be used as a routine summertime diet, providing the cow a reserve capacity for mild heat episodes.

There are times when a cow can experience heat stress for which she cannot cope, even with routine summertime diet and cooling techniques already in place. During these times of stress, using yeast/fungal cultures and water or feed hydration electrolyte products can be very beneficial in reducing the effects of heat and humidity. Current trials with hydration products have indicated less milk loss and better cow comfort by encouraging water and feed consumption. PD

Dr. Robert Ovrebo is a staff veterinarian at the Form-A-Feed and TechMix companies, headquartered in Stewart, Minnesota. For more information, send an e-mail to articleinfo@formafeed.com or call Ovrebo at (800) 422-3649.

Robert G. Ovrebo
Veterinarian with Form-A-Feed and TechMix
articleinfo@formafeed.com