To fully help a heat stressed cow, it is important for the dairyman to understand how her body is reacting and what nutritional requirements need to be met during this period.

To help with this understanding, what follows are four key outcomes of a cow experiencing heat stress. Note that these are not necessarily isolated challenges, but are interrelated.

  1. Dehydration
    • 66% of body fluid is contained within cells, 34% in the soft tissue compartments,
    digestive, and vascular systems.
    • Water is required to carry and distribute nutrients and provide fluid for the fetus.
    • Water will be utilized for managing heat stress first, then maintenance systems
    • Dehydration reduces fluids and nutrients transferred to the cells
    • 7-8% dehydration levels show impaired immune response
  2. Circulatory and Nutrient Disruption
    • Blood flow is directed to the surface layers of the body to cool, putting the
    digestive system at risk of becoming hypoxic (low oxygen)
    • Intestinal toxins can enter circulation and cause inflammation and poor health
    • Cells and tissues are deficient in required nutrients and don’t function properly
    • Potassium depletes due to low feed intake, sweating, and dehydrationeduced
  3. Feed Intake
    • Digestion increases body heat so cows will eat less in an attempt to manage
    • Heat stress accounts for a 50% drop in feed intake while decreased feed intake
    accounts for 50% of the drop in milk yield
    • Bout feeding during cooler periods of the day creates risk of acidosis
    • Low intake of magnesium leaves cow at risk of hypocalcemia
  4. Reproductive Compromises
    • A nutrition deficit contributes to prolonged postpartum anestrus and
    impairs follicular maturity
    • Inadequate nutrient intake reduces body condition score and finally cessation
    of estrus cycles
    • Vitamin E and selenium work to reduce the incidence of retained placenta
    • Cows with retained placenta can have longer postpartum intervals to first
    ovulation and more uterine infections
    • Cumulative effects of heat stress events can compromise the success of
    gestation year round

Read more about ways to combat heat stress in dairy cows at Tech Mix here.