Heat Stress

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Heat Stress
Everybody talks about the weather, but nobody
does anything about it. Charles Warner, 1890
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Heat Stress in Dairy Cows

• Indicators of Heat Stress
• Increased body temperature (gt102.5º F)
• Increased respiration rate (gt80 breaths/min)
• Increased water intake and sweating
• Reduced activity and more cows standing
• More crowding around the water tank
• Reduced feed intake (gt10-15)
• Reduced milk yield (10-20 or more)

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Heat Stress in Dairy Cows

• Impacts of Heat Stress
• Milk production
• Reduced daily output
• Reduced lactation peaks
• Reduced milk component levels
• Higher SCC levels

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Heat Stress in Dairy Cows

• Impacts of Heat Stress
• Reproduction
• Reduced estrous activity
• Reduced estrous duration
• Reduced heat detection
• Reduced follicular development
• Reduced oocyte quality
• Reduced semen quality
• Reduced conception rate
• Reduced pregnancy rate
• Multiple ovulations increased twinning

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Heat Stress in Dairy Cows

• Impacts of Heat Stress
• Pregnancy/Early lactation
• Decreased uterine blood flow
• Increased embryonic death
• Reduced placental mass
• Reduced fetal tissue growth
• Reduced mammary tissue growth
• Early calvings
• Light, weak or dead calves
• Lower colostrum immunoglobulin (IgG)
• Lower colostrum protein, fat, and lactose
• Lower calf blood protein levels

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Heat Stress in Dairy Cows

• Impacts of Heat Stress
• Feed intake/Digestion
• Reduced dry matter intake
• Increased feed sorting
• Increased feed refusals
• Reduced rumen contractions
• Reduced natural buffering capacity due to reduced
  saliva production and increased carbon dioxide
  expiration
• Increased loss of minerals due to sweating,
  panting, and urination
• Increased metabolic disorders

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Heat Stress in Dairy Cows

• Impacts of Heat Stress
• Cow health
• Suppressed immune function
• Increased mastitis incidence
• Increased retained placenta
• Higher ketone levels at calving
• Higher NEFA levels at calving

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Heat Stress in Dairy Cows

• Strategies for minimizing heat stress
• Provide adequate drinking water.
• Provide shade.
• Reduce parlor walking distance.
• Reduce time in holding area.
• Improve ventilation.
• Add holding area/exit lane cooling.
• Cool close-up cows.
• Cool fresh/early lactation cows.
• Cool mid- and late-lactation cows.

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Heat Stress in Dairy Cows

• Dietary Modifications
• Fiber Non-fiber carbohydrates
• Fiber can increase a cows heat load.
• Fiber is essential to rumen health.
• Target for 19 ADF, 30 NDF, and 21 forage NDF
  using high quality forages
• 8-12 on top screen of Penn State shaker box
• NFC levels lt 40

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Heat Stress in Dairy Cows

• Dietary Modifications
• Fiber Non-fiber carbohydrates
• Try to avoid increasing the grain feeding
• Heat stressed cows at greater risk for acidosis
• Decreased buffering capacity saliva panting
• Decreased rumen contractions
• High grain diets during hot weather
• Decrease rumen pH
• Increase rumen ammonia and lactic acid

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Heat Stress in Dairy Cows

• Dietary Modifications
• Fat supplementation
• Are energy dense have a low increment
• Will improve energy balance

based on 50 lbs of dry matter intake
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Heat Stress in Dairy Cows

• Dietary Modifications
• Protein
• Try to keep less than 18
• Consider raising UIP slightly
• Excess nitrogen must be excreted from the body,
  increasing workload of kidneys liver

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Heat Stress in Dairy Cows

• Dietary Modifications
• Water
• Water needs increase significantly with heat
• Water acts as a heat sink
• Add water tanks/troughs in return lanes/pens

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Heat Stress in Dairy Cows

• Dietary Modifications
• Feeding strategies
• Feed multiple times per day
• Feed at cooler times of the day
• Ration Guard to minimize heating in bunk
• Add water ??????

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Heat Stress in Dairy Cows

• Dietary Modifications
• Minerals/Buffers
• Increase sodium levels
• Increase sodium levels to .55-.65
• Sodium bicarb or Sodium sesquicarbonate (.50-.70
  lbs/day)
• Offer free choice buffer
• Increase potassium levels
• Increase potassium levels to 1.4 1.9
• 1st choice (most expensive) is DCAD Plus (K
  carbonate) this will help with overall positive
  DCAD
• 2nd choice is Dynamate (K sulfate/Mg sulfate)
• 3rd choice is Potassium chloride (Dyna K)
• Dynamate and KCL dont help with positive DCAD so
  much

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Heat Stress in Dairy Cows

• Dietary Modifications
• Minerals/Buffers
• Minimize excess chloride, if possible
• Chloride levels can go down to .25-.30 in heat
• If increasing Sod. Bicarb/sesquicarb levels,
  consider dropping salt level to .15 lbs/head/day
• Increase magnesium level if increasing potassium
• Maintain KMg ratio of 4-51
• Magnesium levels of .30-.40
• Magnesium oxide, magnesium sulfate, or Dynamate
• Consider free-choice salt/bicarb

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Heat Stress in Dairy Cows

• Dietary Modifications
• Other additives
• Yeast (Ridley Yeast Culture Concentrate)
• Stabilize rumen environment
• Increase forage digestion dry matter intake
• Complexed Zinc Biotin
• For hoof health/somatic cell count

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Heat Stress in Dairy Cows

• What to watch for
• TMR particle size and sorting
• Cud chewing
• Manure consistency
• Fat/Protein inversions