Dairy effluent — disease and animal health

Dairy effluent requires careful management to prevent animal health problems associated with excess potassium, nitrogen and microbes. This page provides some precautionary steps that can reduce the risk of sick animals.

Minimising impacts associated with excess potassium and nitrogen

Effluent contains high levels of potassium. High potassium levels in soil and pasture can alter the metabolism in the cow and can lead to a deficiency in both magnesium and calcium. A deficiency in magnesium in the cow can contribute to grass tetany and a deficiency in calcium can contribute to milk fever.

Strategies to avoid metabolic disorders associated with dairy effluent management include:

• Regular soil testing of pastures, particularly areas where effluent has been applied to help identify paddocks with higher potassium levels. Cows that are close to calving should have restricted access to pastures with high potassium levels.
• Fertiliser applications can be adjusted and/or effluent application areas expanded to reduce potassium build-up. Further information can be found at the Fert$mart website.

Effluent also contains high levels of nitrogen, so care should be taken to avoid nitrite poisoning. Pasture and crops should not be grazed for at least 21 days following effluent application.

Minimising impacts associated with microbes in effluent

Dairy effluent can contain a wide variety of bacteria, viruses and parasite eggs. Most of the microbes from cow manure are quite harmless. A few are potentially dangerous to cattle and can survive for long periods in moist shaded environments. Some of the key pathogens identified by Dairy Australia (2008) which can have human and animal health implications include:

• Bacteria
  • – Salmonella spp.
  • – Escherichia coli
  • – Listeria monocytogenes
  • – Mycobacterium paratuberculosis (cause of Johne’s disease)
  • – Campylobacter jejuni
  • – Leptospira spp.
• Protozoa
  • – Cryptosporidium parvum
  • – Giardia spp.

Animal contact with microbes

Since older cattle have been constantly exposed to manure, they generally have a high inherent resistance to infection by the microbes it contains. 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 prior exposure to boost 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. Bovine Johne's disease is a particular threat on dairy farms, so precautions with young stock should always be taken.

Irrespective of an animal’s age, unnecessary contact between effluent and animals should be minimised. Major sources of contamination are those areas of high animal density such as calf sheds, calving pads, feedpads, laneways and loafing areas. These should be well drained, regularly cleaned or scraped to keep them 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.

Management strategies to maintain animal health

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

• Never graze effluent application areas with young stock (less than 12 months of age).
• Apply effluent at agronomically appropriate rates and rotate application areas. Further information can be found at the Fert$mart website.
• Storing effluent (in effluent ponds) for extended periods will help to kill potentially dangerous bacteria and viruses.
• Raw effluent is usually diluted with washdown water, which will minimise the concentration of harmful microorganisms applied to an area.
• A withholding period of at least 21 days before grazing after an effluent application 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 removing microbes from the grass and ensuring that sunlight can penetrate to the soil surface.
• Spreading effluent in hot dry weather enables the ultraviolet radiation in sunlight to reduce the number of microbes.
• Equipment used to handle dairy effluent should be thoroughly cleaned before moving between farms to ensure that microbes are not spread from farm to farm.
• Composting of calf bedding material and manure stockpiles to at least 60 degrees for 3 days can help to kill most microbes. See Composting for more information on how to compost.
• Excluding cattle and calves from farm water supplies and waterways will help to maintain farm water quality by reducing effluent entering the waterway or water supplies. Establishing vegetative buffers around water supplies can also help to filter sediment where microbes live.

Risk of human health issues

Dairy shed effluent should not be a threat to human health so long as the usual hygiene measures are followed 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. Keeping up to date with vaccinations such as Q Fever will also help to ensure a safe workplace.

Sound effluent management and grazing practices are paramount for minimising unnecessary health risks to the herd and maintaining top milk production.

References

Dairy Australia (2008), Effluent and Manure Management Database for the Australian Dairy Industry, 4 June 2021

Dairy Australia (2021), Fert$mart – Getting it right, 16 June 2021