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Prepare Now For Heat Stress

Weather has an enormous impact on our industry; everything from precipitation concerns to temperature extremes affecting our crops and livestock.  This past winter was one for the record books, now it is time to prepare for warmer temperatures and reduce the impact of heat stress on your dairy and feedlot cattle.  We now have a better understanding of the impact that brief periods of low rumen pH can have on animal performance.  Periods of low rumen pH can result in reduced rumen function, death of rumen bacteria and systemic endotoxemia.

There are many modifications we can make to the housing environment to lessen the impact of heat stress.  Now is the time to check your water supply, fans, sprinklers and the condition of your shades. However I want address some nutritional modifications with this blog.  Dairy cattle and beef feeder cattle are more susceptible to heat stress today than cattle were just 10 years ago due to being at higher level of performance and changes in housing conditions.

We have high performance animals that produce a great deal of heat on a normal day.  Regardless of the size of the dairy, we must milk the cows.  The holding pen and milking parlor can be one of the hottest and humid places on earth.  Imagine an entire pro football team packed in a school bus after a pre-season half-a-day work out in August………times 10. It can take dairy cows hours to cool down after a trip through the holding pen and milking parlor. 

Our diets are designed to match the performance potential of our animals; highly fermentable, high energy diets. Periods of heat stress will result in fewer, but larger meals consumed during the cooler times of the day.  Cattle will be more aggressive at sorting the ration.  The result is increased risk of periods of reduced rumen pH, often referred to as sub-acute rumen acidosis (SARA). The severity of SARA is dictated by how low and how long the rumen pH is depressed.  A common nutritional recommendation is to increase the amount of buffers in the ration.  However, how beneficial are buffers in the ration if the cattle are going several hours without eating the ration?  In addition, when cows eat fewer meals during the day the amount of starch (a high fermentable carbohydrate) consumed in a single meal may over whelm the buffering capacity of the ration.  Offering a self-fed buffer supplement is a tool that many producers utilize during periods of heat stress.  CRYSTALYX® BufferLyx® and CRYSTALYX® Meta-bolyx® are low moisture block formulas that have the advantages of less waste, higher palatability and more consistent predictable intake as compared to free choice buffers like sodium bicarbonate and magnesium oxide. 

Research has shown these formulas to be effective at minimizing the severity and duration of depressed rumen pH in a SARA challenge.  See Figure 1.  The SARA challenge model developed by Dr. Gary Oetzel of the UW-Madison School of Veterinary Medicine simulates conditions where intake has been limited to 50% of normal and cattle were allowed full access to the ration and given additional grain.

Figure 1.  BufferLyx® Treatment Had Higher Rumen pH and Quicker Recovery Time.

Field observations and third party research trials have shown milk and performance responses that are very impressive; +4 to +9 pounds of milk and +0.25 lb./hd/day ADG in hard fed Holstein steers.  Honestly hard to believe!  Subsequent research using this SARA model has helped explain why and how minimizing the periods of low rumen pH can result in this improved performance.

The rumen is a large fermentation vat containing billions of bacteria and protozoa.  Many of these bacteria are gram negative bacteria that have a lipopolysaccharide (LPS) component to their cell wall.  LPS is a potent toxin that causes fever, reduced immune function and changes in insulin sensitivity which will impact energy metabolism.  LPS is the endotoxin responsible for the severe swelling, pain and fever associated with E. coli mastitis and E. coli diarrhea.  Rumen bacteria are very sensitive to pH and will rupture and die when the pH is too low.  This causes a release of the LPS into the rumen.  When large numbers of bacteria are killed during heat stress induced SARA the LPS released will cause localized inflammation and the LPS enters the blood stream.    Subsequent research by Khafipour et al. using the SARA model found that LPS levels were greatly elevated in the rumen fluid and in the blood of animals experiencing a single SARA event.   

Adapted from Khafipour et al. JDS 2009

Adapted from Khafipour et al. JDS 2009

The impact of low rumen pH worsens with each subsequent SARA event and it takes a long time for these animals to recover from just a single SARA event.  The damage and inflammation caused by the LPS release has long term implications on the rumen’s ability to recover and regenerate new tissue.  This explains the common observation that after the third or fourth event of summer heat stress the herd crashing in milk production. 

Dohme et al. conducted a study where the SARA challenge was repeated every 10 days for 3 times in total.  Monitoring the amount of time spent below rumen pH of 5.8 and 5.5 was how this trial ranked the severity of the acidosis.  The research concluded that cows will experience increasing severity and duration of low rumen pH with each additional challenge as indicated in the graph.   Fiber digesting bacteria are killed below rumen pH of 5.8 and rumen function is altered when rumen pH is below 5.5 for extended periods. 

Look at Challenge Period 3 in the graph below and notice the time under the dotted line (pH 5.8).   The rumen pH for cows in the SARA challenge was below pH 5.8 for 13.9 hours/day compared to 4.7 hours for control cows.  SARA challenge cows experienced rumen pH below 5.5 for 9.5 hours/day compared to 1.8 hours/day for control cows.  These finding can help explain why it appears the herd crashes.  Not every animal in a herd is impacted to the same extent by heat stress.  In reality the herd crash has been building as more and more individuals in the herd are having a 3rd or 4th sub-acute acidosis event.

Adapted from Dohme et al. JDS 2008

Adapted from Dohme et al. JDS 2008

SARA cost the dairy and beef feed lot industry billions of dollars in lost performance.  Heat stress is a contributing risk factor for SARA.  Heat stress abatement with modifications to the housing environment will help keep the animals cool, but do not forget nutritional modifications.  Research has shown that 1 brief period of low rumen pH makes animals susceptible to more severe acidosis risk with the next challenge.  SARA not only impacts rumen function but can contribute to systemic endotoxemia which will impact health and reproduction. CRYSTALYX® BufferLyx® and Meta-bolyx® offer a convenient self-fed buffer supplement that helps reduce the severity of SARA risk by improving the buffer status of the animals regardless of ration intake.