In my travels this week I have seen rows of corn emerging from recently planted fields and even a few fields of mowed hay.  All indication of a warm spring which will lead to summer time temperatures and the risk of reduce animal performance due to heat stress.

Temperature Humidity Index for dairy cows (left) and humans (right). Source: www1.extension.umn.edu

People tend to enjoy the warmer weather and some people even like the hot summer temperatures. People start to experience mild heat stress around 80° F.  This is in stark contrast to our cattle that begin to experience mild heat stress at 72° F and 40% humidity.  Humidity adds significantly to the stress.  From personal experience 80° F in Kentucky at 70% humidity is more uncomfortable than 80° in Wisconsin by a long shot.   The list below is a review of the impact heat stress can have on dairy cattle.

• > 68: Temperature Humidity Index (THI) where mild heat stress begins in dairy cows
• 80: THI where moderate to severe heat stress begins
• 8-12%: potential decrease in dry matter intake (DMI)
• 10-25%: potential decrease in milk production
• 35-50%: of the decline in milk yield that is explained by decreased DMI
• 7-25%: increase in maintenance energy requirement of cows during heat stress
• 2 hr./day more a cow will spend standing during heat stress (THI > 70)
• 1,000-2,000: reduced milk yield (lbs.) in the lactation after dry cows experience heat stress

Beef Cattle and Heat Stress

How do you measure the success of your heat stress abatement program?  The impact of heat stress can be significant.  The majority of spring born calves will be nearing finished weights in July and August.  In comes the summer heat and intakes drop, gains slip and cattle just don’t finish.  Water demand exceeds capacity and nearly finished cattle start dropping dead.  You may have said in the past that you could not afford to prepare for heat stress.  Today just 1 dead 1400 pound fat will cost you about $3000.  $3,000 will buy a fair amount of shade cloth, extra water tanks and supplements to minimize the effects of heat stress.  In reality the losses happen long before animals start dying.   The list below is items to consider for beef cattle.

• 80°: THI where moderate to severe heat stress begins
• Cattle nearly finished are at increased risk
• 15-20%: potential decrease in dry matter intake (DMI)
• The decrease in DMI may be difficult to reverse
• 50 to 100%: increase in water intake
• Changes in eating patterns at 75°
• Increased standing time which can impact hoof health

Facility Considerations

• Shade to reduce heat load, especially for dark hided cattle
• Add water capacity by adding poly water tanks
• Add water delivery capacity by adding wells or storage capacity
• Add sprinklers to feed bunk lines
• Develop a plan for hosing down cattle during severe heat stress
• Add fans in confinement buildings
• Do NOT work cattle during heat stress

Ration and Feeding Considerations

• Deliver feed during cooler times of the day
• Consider a ration additive to minimize heating of the mixed ration
• Dairy – consider additives such as yeast culture, niacin, Tasco^® and betaine
• Beef and Dairy – increase buffer level, Na, K and Mg levels, fat and Vitamins
• Minimize the impact of sub-acute rumen acidosis (SARA) due to slug feeding

CRYSTALYX^® Buffer-lyx^® and Meta-Bolyx^® are self-fed supplements that will assist with maintaining rumen health and DMI by minimizing the impact of SARA due to the unique deliver of added buffers and the stimulation of the natural buffer effect of saliva recirculation due to the licking action.  Don’t wait until it’s too late!  Be proactive with reducing the deadly effects of high temperatures.