Dairy effluent — disease and animal health

Dairy effluent provides a rich source of nutrients and water that can be used to grow more feed. But high levels of certain nutrients in plants have the potential to cause some animal health issues.

Microbes found in effluent can also cause problems. There are some basic precautionary steps that can drastically reduce your risk of getting sick cows.

Pastures with high nutrient levels

Effluent contains high levels of potassium. As potassium in the soil increases, nutrients such as magnesium and calcium are replaced by the potassium.

This  means the grass and the cow's diet are deficient in both magnesium and calcium. This can then lead to grass tetany (deficiency in magnesium) or milk fever (deficiency in calcium).

Cows —  especially those close to calving —  should avoid eating pastures with high potassium levels. Nervous cows are an early warning sign of animals that have been grazing high potassium pastures.

Effluent also contains nitrogen, so care should be taken to avoid nitrite poisoning. Where possible, pasture and crops should not be grazed for 21 to 30 days following effluent application.

Effluent microbes

The majority of waste in dairy effluent consists of:

  • urine
  • uterine discharges
  • milk
  • saliva
  • faeces.

This waste material can contain a wide variety of bacteria, viruses and parasite eggs. Most of the microbes from cow dung are quite harmless, and many microbes, like those that cause mastitis and leptospires can't survive. A few are potentially dangerous to cattle and can survive for long periods in moist shaded environments. These include:

  • Salmonella sp
  • Yersinia sp
  • Mycobacterium Para tuberculosis — cause of Johne's disease, worm eggs, coccidial and Cryptosporidium cysts and rotavirus.

Animal contact with microbes

Since older cattle have been constantly exposed to dung they generally have a high inherent resistance to infection by the microbes found in dung. If effluent is spread on the farm of origin, it is probably safe to assume that there will be nothing in it that the adult cattle on the farm haven't already been exposed to.

However, calves and yearlings are much more susceptible to infection as they have not had time to develop their immune systems. This is the reason why vets recommend that young cattle be kept separate from adult cattle.

Young stock should not be exposed to paddocks where effluent has been spread within the past year. Johne's disease is a particular threat and any farm is susceptible so precautions with young stock should always be taken.

Independent of age, unnecessary contact between effluent and animals should be minimised. Major sources of contamination are those areas of high animal density such as feedpads, laneways and loafing areas. These should be well drained, cleaned or scraped to keep it free of stagnant effluent and any stored effluent should be stockpiled away from cattle.

All measures should be taken to ensure cows are not unnecessarily in contact with effluent microbes.

Reducing animal health risk

Some management practices  will help to minimise the risk of cattle being exposed to harmful microbes.


  • Never graze effluent disposal areas with young stock.
  • Spread effluent over a large area to prevent excessive nutrient build-up.
  • Storing effluent (in effluent ponds) for extended periods will help to kill dangerous bacteria and viruses.
  • Diluting the effluent with the washdown water will minimise the concentration of harmful microorganisms applied to an area.
  • A withholding period of at least 3 weeks before grazing after an application of effluent will help minimise the live microbe population.
  • Grazing pastures before the application of effluent will ensure that they will not need to be grazed for several weeks, maximising the chances of rain washing microbes off the grass and ensuring that sunlight can penetrate to the soil surface.
  • Spreading effluent in hot dry weather enables the ultra-violet radiation in sunlight to reduce the number of microbes.
  • Not grazing a crop or pasture for at least a couple of weeks after effluent was last spread.
  • Equipment used to handle dairy effluent should be thoroughly cleaned before it is used on another farm to ensure that microbes are not spread from farm to farm.

Risk of human health issues

Dairy shed effluent should not be a threat to human health so long as the usual hygiene measures are taken when working with the material. These include not smoking, eating or drinking while working and washing hands and clothing at the completion of the task. As aerosols can be generated by manure sprinklers and travelling irrigators, it is wise to avoid areas where effluent material is likely to settle on the skin or be breathed in.

Sick cows will cost you money. Sound effluent management and grazing practices are paramount for minimising unnecessary health risks to the herd and maintaining top milk production.

Page last updated: 14 Jan 2021