Without proper management, heat stress can reduce cattle comfort and overall productivity by forcing a change in the normal balance of the body’s biological systems.

Properly identifying and minimizing stressful situations optimizes health, growth and reproductive efficiency of the animal and provides economic benefits to the producer.

The first step in minimizing heat stress is to understand when it occurs. Heat stress in cattle begins before we (humans) feel uncomfortable.

In fact, Ted Perry, marketing beef nutritionist with Land O’Lakes Purina Feed, LLC, estimates that cattle feel the effects of heat at about 70ºF and can become critical with temperatures as low as 85ºF with high humidity.

“Producers need to be aware that cattle are feeling the effect of heat when they themselves are comfortable,” Perry says. “A good rule of thumb is that if you are using air conditioning in your truck, your cattle are feeling some heat stress.”

Perry says grazing cattle should be monitored for heat stress when outside temperatures reach 70ºF
and above.

Signs of heat stress include crowding around water tanks or under shade, panting and increased salivating. High respiration rates also plague stressed cattle.

Perry explains that moderate heat stress is signified by 80 to 120 breaths per minute, strong heat stress is indicated when cows breathe 120 to 160 breaths per minute and levels over 160 breaths per minute are a sign of severe heat stress.

Though this general rule is valuable to reference, cattle comfort will vary depending on numerous conditions including age, body condition, genetics, hair coat length, acclimation, animal health and pasture conditions.

Consequently, animals must be monitored individually to prevent the negative side effects of heat stress which include reduction in grazing time, breeding efficiency, milk production and weight gain.

Summer rations and feeding routines

Feed intake is usually the first indicator of heat stress, as the feed digestion process causes cows’ body temperatures to increase.

As cattle heat up and feed intake drops, cattle begin using additional energy to keep cool. Therefore, heat stress can reduce production and efficiency. Once this performance level drops, it becomes very difficult to get it back.

To keep production from dropping during high temperatures, the ration must be managed closely. Pasture often requires supplementation to provide adequate nutrients.

As feed intakes decline with higher temperatures, producers can provide a more concentrated supplement to improve nutrient intake. Creep feed for nursing calves and forage supplements for mature cattle are recommended.

Perry says that one strategy to reduce heat load on cattle is to offer a majority of the added feed in late afternoon.

“Cattle consuming diets during the late evening hours may be better able to cope with the heat load of fermentation due to timing,” he says. “When fed later, the heat increase occurs during the coolest part of the day.”

Pasture supplementation

If forage supplementation becomes necessary, feed additives can be useful to keep cows eating. Additives that modify intake cause cattle to consume multiple small snacks of the supplement throughout the day.

The supplement optimizes the flow of nutrients to the digestive system, increasing forage utilization and optimizing cattle performance.

Additionally, increased water consumption during the heat of the summer will increase excretion of urine. This will augment the loss of certain minerals, such as sodium, potassium and magnesium.

To maintain a mineral balance, provide a quality, properly balanced mineral mix that includes salt in a location that the cattle will consume it.

In addition to breeding, production and body condition benefits supplied to the cow, supplements can also potentially benefit fall-born calves.

Research suggests that the gestational nutrition of the dam imprints the lifetime genetic potential and performance of subsequent generations.

The performance of a calf is influenced not only by nutrition in-utero and immediately after birth but also by the prior fetal nutrition of both its dam and granddam.

For this reason, combined with the benefits provided to the cow, a year-round supplement plan should be created.

A proper nutrition program can enhance reproductive efficiency, cow body condition score and animal performance.

Speak with your local dealer, sales specialist and beef consulting nutritionist to
determine the appropriate supplementation for your cattle’s needs to optimize consistent intake and performance. 

References omitted due to space but are available upon request. Click here to email an editor.

PHOTO

Utilize shade in the hottest parts of the day to cool cattle and free them from confined areas. Photo courtsey of Progressive Cattleman staff.

Heat stress prevention tips

The best way to prevent heat stress is to anticipate the problem, observe the cattle frequently and take necessary precautions before productivity drops. Tips to consider include:

• Turn cattle out rather than keeping them confined if shade is available. Shade can be provided by trees, sunshades or access to an open building. If cows are indoors, adjust the ventilation in buildings to allow free air circulation.
• Provide easy access to clean, cool drinking water. Check water sources frequently for problems and provide additional tank capacity as water intake increases. At temperatures above 80ºF, each cow may need in excess of two gallons of water per hour for each 100 pounds of bodyweight.
• Consider the type of cattle you are working with. Cattle most at risk for heat stress include newly received cattle that have experienced a fair amount of weaning, processing and transportation stress; cattle that have been sick in the past and may have pre-existing lung damage; black or dark-hided cattle; cattle that are or have been grazing endophyte-infected fescue (typically taller fescue in late summer); older cows and heavy bred cows that will calve during the summer months.
• Sort and move cattle only during the cool periods of the day (before 8 a.m.) using low-stress handling techniques. Ted Perry, marketing beef nutritionist with Land O’Lakes Purina Feed, LLC, estimates that it takes six hours to dissipate body heat when temperatures are low enough to allow cooling. During summer heat stress, this takes much longer. Holding and processing areas should have shade and sprinklers available.
• Producers using managed intensive grazing are encouraged to rotate paddocks at a more rapid rate. Taller grass tends to be a cooler surface to maintain cattle on than pastures with shorter grass stands. Rotate cattle in the evening rather than the morning, as grass consumed in the evening will digest overnight and heat dissipation will be complete by mid-morning.

Steven Myers

Consulting Beef Nutritionist
Land O’Lakes Purina Feed, LLC