Heat Stress in Dairy Cattle

horizontal ruleAll cows are affected by heat stress.  Their comfort zone is between 4°C-24°C without relative humidity.  Milk depression at 35°C can be as much as 33%.  While we might think temperatures in our region are not alarming, we have to remember this is the temperature adjusted for humidity in the stall, at the bunk and in the holding area.

Visible signs of Heat Stress in Dairy Cattle

  • Decreased activity.
  • Refusal to lie down.
  • Increased respiratory rate (open mouth panting).
  • Open mouth and laboured breathing.
  • Sweating and excessive drooling.
  • Reduced food intake.
  • Agitation and restlessness.
  • Thirst is increased. Drinking water intake increases.
  • Increased urination (with heavy electrolyte loss).
  • Crowding over the water troughs.
  • Loss of milk quality – fat and protein content declines.
  • Loss of body weight.
  • The incidence of milk fever increases.
  • Laminitis is more frequent.
  • Keto-acidosis is a recurring problem.
  • Fertility is lowered – insemination success rate falls.
  • Increased somatic cell counts and risk of Mastitis.
  • Embryo mortality increases.

Invisible signs of heat stress in Dairy Cattle

  • Ruminal pH is typically lower in heat stressed cattle. Rates of gut and ruminal motility are reduced, thus slowing passage of feed through the digestive tract.
  • Increased peripheral blood flow.
  • Some indigestibility of feed.
  • The huge water flux resulting from increased water consumption also causes heavy loss of electrolytes.
  • Alter the production of reproductive hormones essential for pregnancy. Changes the balance of developing follicles in the ovary.
  • Embryonic development is affected.
  • Bicarbonate (HCO3) is lost.
  • Stress hormones appear in the blood.
  • Gene function is disturbed.
  • Heat shock proteins are activated to shut down metabolic reactions and to protect heat-sensitive tissues.

Mitigating Heat Stress will make you money!  Here are some ways.

  • Increasing availability of fresh water.
  • Ventilation in holding area
  • Ventilation at the bunk and stalls
  • Avoiding over-stocking


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