Combating Heat Stress in Lactating Dairy Cows

By Tracey Erickson

With summer temperatures and higher humidity levels upon us, dairy producers need enact their heat abatement strategies on farm for all livestock. Dairy cattle have a comfort zone of between 41 to 68 F°. When the ambient temperature goes beyond 68 F° dry matter intakes will decrease on average 0.17 lbs. for each degree above 68 F°. For every 1-pound loss in dry matter intake it is estimated that 2 pounds of milk are not produced.

Common heat stress outcomes include a reduction in dry matter intake and increased water intake which results in a drop in milk production and butterfat, along with potentially increased reproductive issues such poor conception rates and pregnancy loss, along with possible rumen acidosis. Other heat stress indicators include: increased body temperature, open mouth panting, increased respiration, sweating, increased amount of time standing, and changes in manure consistency.

Management Considerations

What can you as dairy producers do to help aid in the reduction of heat stress in the lactating dairy herd? What follows are some basic tips for dairy cattle heat stress reduction:

• Increase access to clean, fresh drinking water. This may involve adding extra tanks of water and checking for appropriate flow of water in drinking fountains. Consider adding temporary water access such as a split PVC pipe with flowing water or portable tank to cows as they leave the parlor.
• Cattle that are being exposed to a holding pen in a parlor should be cooled by a combination of air movement, water sprinkling systems, and shade. DO NOT use sprinklers in holding areas without fans; it creates a “sauna” effect in the holding area.
• Make sure to use large droplets of water when sprinkling (soaking) cows, small droplets often found in misters will not allow for heat dissipation from the cow. Intermittent cycles allow time for the water to evaporate and cool the animal before the next cycle. Sprinkle cows with low pressure sprinklers over their backs away from the feed bunks. Trying to keep the udders dry in this process will help minimize the incidence of mastitis.
• Recommended air exchange rates either natural (wind) or mechanical (fans) for proper ventilation to cool cows during hot weather is 470 cubic feet per minute (cfm) for each 1,400 lb cow (MWPS, 2013).
• Use large fans in combination with sprinklers to help cool cows and the air simultaneously.
• Make sure all fans are working while providing the proper maintenance and cleaning.
• Make sure all curtains and thermostats are in proper working order in naturally ventilated barns and that you are able to maximize the open side-wall.
• Provide shade if cattle have access to an outside lot.
• Adjust diets accordingly, as dry matter intake decreases, utilizing higher quality forages and increasing the energy density of the diet. As diet adjustments are made, care should be taken to make sure that there is enough effective fiber is available to maximize rumination and keep acidosis and displaced abomasum’s to a minimum. Work with your nutritionist to obtain a proper ration.
• Adjust feeding delivery to the cooler times of the day and increase the number of times feed is pushed up to minimize sorting.
• Manage high moisture feeds such as gluten and distillers’ grains to reduce secondary fermentation.
• Maximize feed quality by removing feed refusals before the fresh TMR is delivered and by not allowing excessive wetting from misters to occur.
• Remove only as much silage or haylage as necessary from the bunker face to minimize spoilage and secondary fermentation starting to occur.
• Increase the delivery of key minerals and dietary supplements: Phosphorus, Potassium and Sodium and dietary supplements:
• Potassium levels increased heat stressed cows from 1.0% to 1.5% has shown an increase in milk production in research trials (Schneider et al., 1984)
• Research also has shown a benefit to increasing the dietary cation-anion difference (DCAD) in lactating cows with sodium (sodium bicarbonate) and potassium (potassium carbonate).
• Research has also shown feeding yeast culture in TMR’s, when cows are experiencing heat stress will improve milk yield by 2.6 lbs. per day (Bruno et al., 2009)
• Diets should contain at least 0.25 lbs. of white salt per cow per day, along with offering access to free choice salt and trace minerals.

As we know cow comfort is essential for high milk production especially during periods of heat stress. Taking the time to focus on cow comfort aids, such as additional fresh clean water, air movement, shade and evaporative cooling, while providing energy dense, properly balanced, palatable diets will help minimize lost milk production and reproductive efficiencies due to heat stress.