Grazing abundant clover pastures
Tablelands Telegraph – February 2021
Bruce Watt – Senior District Veterinarian
On several properties in the last couple of months, owners and managers have discovered quite a few big, fat, previously healthy British breed cross ewes that are either dull and sick or dead.
Our vet team has been called to several of these properties.
When we autopsied a sample of the dead ewes, we found that the fat is often bright yellow, and the kidneys were swollen and black. Laboratory testing confirmed high liver, kidney and blood levels of copper.
Barber’s pole worm infestation is always a possibility especially at this time of the year. In seasons like this, copper poisoning symptoms to look for are pale dirty grey or yellow colouration of the membranes around the eyes and gums.
Copper poisoning is well known as a cause of death in fat ewes on clover in the spring and summer. Classically it known as toxaemic jaundice and occurs in ewes with previous liver damage usually from heliotrope or Paterson’s curse. The damaged livers accumulate copper until it reaches a tipping point. The subsequent sudden release of copper, often triggered by handling, causes the red cells to rupture releasing haemoglobin, the breakdown products of which cause jaundice, black damaged kidneys, sickness and death.
Image – Bright yellow fat in an ewe that has died from copper poisoning
This year however, we have not found evidence of significant prior liver damage. We think that the abundant clover alone, growing as it often has since March, on high copper soils, has been enough to cause the poisoning.
Ewes can be treated with a molybdenum and sulphate drench to bind the copper. While this is reasonably effective it may need to be repeated a few weeks later. Some producers have also used blocks or loose mixes containing molybdenum and sulphate with variable success.
Last year has been one of the best of record and we look forward to another like this as soon as possible. However, there have been a few stock problems and copper poisoning on clover is another for us to watch out for.
Our District Veterinarians are a valuable resource for local and independent advice on biosecurity and animal health issues. They can investigate herd and flock problems to help maintain a productive and secure local livestock industry. Contact the team if you have issues with your livestock.