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Changing of the Seasons: Preparing for Summer Heat Stress In Dairy Cattle

Warmer weather is a welcome relief from the long winter and a cooler than normal spring in many areas of the country.  In parts of the Midwest, we experienced early May snows followed within 2 week by summer like temperatures.   Most people welcome the return to the 70s or 80s; however cattle and especially dairy cattle prefer the cooler temperatures.  Now is the time to prepare for management and nutrition changes that will help our cattle handle the heat.  I will address heat stress in dairy cattle in this week’s blog and then address some unique aspects of the impact of heat stress on beef cattle next week.   

Physiological Responses to Heat Stress

Evaporative cooling is the most effective means for an animal to cool itself.  Core body heat is transferred to the skin and the heat is dissipated to the surrounding air through evaporative cooling of sweat or water from sprinklers.  The level of evaporative cooling is very dependent on humidity and air movement.  Cattle in confinement will benefit from the addition of fans and sprinklers to a heat stress prevention program.  Do not forget the importance of shade and water for your dry cows and heifers.  Studies have shown a return for supplemental cooling for dairy cattle in the transition period.  Cattle are inefficient at cooling themselves through sweating alone.  As temperatures increase, an animal will transfer heat through the moisture in the air it exhales.  This is seen as open mouth breathing and excessive drooling of saliva.  Responses of cattle to heat stress are related to these physiological responses.  Our job as caretakers is to maximize the effectiveness of cooling and to minimize any negative aspect of these responses.

Temperature Humidity Index Updated for Today’s Dairy Cattle

The performance level of cattle in general has increased over time.  The negative impact of heat stress starts earlier than you would expect.  From a metabolic standpoint, the higher milk production creates more heat.  Housing systems have changed to higher animal densities especially in milking centers.  The Temperature Humidity Index (THI) takes into account both temperature and humidity.  The original THI for cattle (see chart) was developed around 1960 and it was generally accepted that dairy production was negatively impacted at a THI of 72, however due to higher animal performance levels the negative impact of heat stress for dairy cattle actually starts at a THI of 68.

Yellow – Mild stress; Orange- Moderate; Red – Moderate to Severe; Purple – Severe Stress

CRYSTALYX® Brand Supplements offers a line of Dairy Formulas that address the unique nutritional challenges created by heat stress.  BufferLyx™ is unique low moisture block that reduces the risk of acidosis by delivering additional buffer agents and highly available trace minerals while stimulating saliva production. Transition Stress ™ Formula is a nutrient dense mineral and vitamin supplement that contains chelated trace minerals and yeast culture. 

Hopefully Mother Nature will give us a little time to transition to severe hot weather. Remember that our cattle will begin to suffer well before we start to complain. Managing the environment of the cattle is a challenge, but intervention with fans, sprinkler and changes to our handling and feeding program can reduce the negative impact of heat stress.