Are your heifers heat stressed? Part II

By Roy Williams, 2010 DCHA Leadership Class member

Heat stress occurs when an animal's body temperature starts to rise above normal due to environmental factors. Air temperature, humidity, air flow around the animal, radiation from hot surfaces, direct and diffused sunlight, and ground temperature all influence the ability of the animal to control its internal body temperature. The animal's breed, age, health, lactation status, hair coat color, and diet also affect its ability to maintain its internal body temperature.

A survey of 40 government agricultural department and university extension websites produced a list of do's and don't's (and maybe's) for combating heat stress.

Do:

• Insure sufficient water supply - cows may drink 1-2 gallons per hour at 90^oF.
• Insure that the water is clean (dirty water will discourage consumption).
• Allow sufficient water trough space - but how much is "enough"?
• Provide shade at all times - at least 50 sq. ft. per adult animal
• Sprinklers that emit large droplets are helpful.
• Occasional spraying with a fire hose is helpful if no sprinklers are available.
• If cattle must be penned, moved, or worked, do it very early in the morning.
• Provide strong airflow at all times (5 to 7 mph or more for adult cows and older heifers).
• Provide plenty of space for each animal to insure good air flow.
• Put cattle in pastures with tall grass (and shade) (tall grass will be cooler than short grass or no grass).
• For cattle not on an always-available TMR feeding program, put out most of the feed in the evening.
• For cattle on pasture, speed up the rotation of pastures to improve quality of forage.
• Be sure that cattle have access to sufficient minerals, due to increased water intake/excretion.
• Reduce fly population to reduce tendency of cattle to crowd together.
• Insure that water troughs are always in the shade.
• Increase the energy density in the feed ration (compensate for reduced DMI).
• Have your water supply checked for minerals and contaminates.
• Run misters a few minutes at a time, then shut off until cows dry off, then run again.
• Use high quality roughage in the diet.

Don't:

• Move or work cattle during the day.
• Subject cattle to procedures that scare them.
• Force cattle to stand in confined spaces or crowded groups where airflow will be diminished.
• Force cattle to stand in direct sunlight.
• Feed large amounts of poor quality hay.
• Force cattle to walk more than 50 feet to water - and never through or into an area in direct sunlight.
• Let cows congregate in the same area day after day creating a mud hole (increases mastitis risk).
• Feed a ration that has more than 65% of the protein in the form of rumen degradable protein.
• Use high-pressure misting systems that produce a fine spray or mist - these increase humidity.
• Move cattle from a cool climate to a hot climate - these cattle will experience greater heat stress.

Maybe:

• Mist systems that emit a fine spray raise the humidity, and may do as much harm as good.
• Mist systems may cause animals to inhale water droplets contaminated with dust from dried manure.

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