Sperm and embryo survival compromised by heat

Sheep-in-drought

Signs of heat stress include continual panting, rapid or open mouth breathing, weakness, inability to stand, and an elevated rectal temperature.

With maximum temperatures exceeding 40 degrees Celsius in most of the Western region this week, Western Local Land Services is reminding producers about steps taken to minimise heat stress on livestock.

These steps include:

  • only handling livestock if it is essential
  • handling in the coolest parts of the day (early morning and late evening)
  • ensuring adequate access to shade and shelter, particularly in yard or feedlot situations
  • access to clean, cool water. Livestock may reject water that is fouled or hot.

In particular, care should be taken when yarding sheep for shearing. A shorn sheep has an increased heat load, as the insulation of the fleece has been removed so the amount of water lost through evaporative cooling is increased.

Shorn sheep can also be susceptible to sunburn. Steps that should be taken to minimise heat stress in newly shorn sheep include:

  • the provision of adequate shade and water (a newly shorn sheep in extreme weather conditions may consume over 80 % more water than normal). In normal conditions, sheep will consume between 4 and 12 litres of water a day depending on age
  • reducing the amount of time off feed and water when yarded
  • pay particular attention to rams that have been sedated for shearing as they lose their ability to regulate body temperature.

Important things to consider are the impact that heat stress can have on livestock long term. Heat stress can affect:

  • sperm production and viability of rams. There may be a seven week delay before newly viable sperm is produced
  • embryo survival in ewes
  • feed intake (may not meet energy requirements)
  • immunity (stock become more susceptible to disease)

Signs of heat stress include continual panting, rapid or open mouth breathing, weakness, inability to stand, and an elevated rectal temperature.

Livestock suspected of being heat stressed should be moved to a cool shaded area and offered cool clean water.

Landholders with questions relating to managing livestock in extreme weather conditions should contact their nearest Local Land Services District Veterinarian:

  • Charlotte Cavanagh, Bourke, 0429 773 021
  • Felicity Wills, Broken Hill, 0409 858 901.
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