boxed-arrow-leftArtboard 1Artboard 1Artboard 1Artboard 1
Open menu

Published: 25 Jul 2019

calf nose

Lesley Irvine and Nathan Bakker, TIA

Do you have visitors to your farm? Do you have stock coming to your property from other farms (purchase, lease or returning from agistment)? Do you have neighbouring properties with livestock? If you answer YES to any of these questions, there is an increased risk of a disease entering your farm.

In June, DairyTas and TIA joined forces to conduct animal health workshops in the main dairying regions of Tasmania to discuss strategies that reduce the risk of diseases entering farms.

The main diseases discussed at these events were:

  • Salmonella
  • Johnes Disease
  • Mycoplasma


Salmonella is a bacterial disease affecting animals and humans worldwide. Symptoms of Salmonella include fever, anorexia, toxaemia, abdominal pain, diarrhoea, dehydration, abortion and death.

Salmonella bacteria can arrive on-farm in several different ways including:

  • Introduction by an infected/carrier animal – infected animals can shed bacteria for up to 10 weeks
  • Contaminated feed
  • Contaminated environment (e.g. soil, birds, rodents, insects, water)

It is important to note that Salmonella bacteria can survive in the environment for extended periods of time. It can also become endemic on a farm, which means it is always present in the environment and only needs a trigger for a new outbreak to occur. This trigger is often stress. Stressors may be:

  • Intensive farming practices (grazing, housing)
  • Recent calving
  • Lack of feed/water – or changes to feed/water
  • Transportation
  • Other diseases
  • Seasonal conditions (e.g. wet/cold)

Johnes Disease

Johnes Disease is a chronic infectious wasting disease. It is caused by the bacteria Mycobacterium paratuberculosis living mainly in the intestines of infected animals. The bacteria cause the intestinal wall to thicken, reducing the ability to absorb nutrients from feed. Therefore, even though an infected animal may be eating enough, both in quality and quantity,  it isn’t able to absorb the required level of nutrients from the feed resulting in loss of production and condition. An infected animal can eventually starve to death.

Like Salmonella, the bacteria causing this disease can survive in the environment for long periods of time (longer than 12 months in cool, moist environments).

Cattle infected with Johnes Disease excrete the bacteria in their manure. The bacteria contaminates pasture and watercourses and the disease spreads to other animals when they ingest the contaminated feed or water.

Most cattle are infected when calves – calves are considered most at risk during their first 30 days of life. However, symptoms of Johnes Disease do not develop for many years. Infected cattle are likely to be shedding bacteria before clinical signs of the disease are evident.

There is no treatment for Johnes Disease although there is now a vaccine available to prevent cattle being infected.


Mycoplasma is also a bacterial disease. It is caused by the bacteria Mycoplasma bovis. It can affect cows in different ways and symptoms can vary from farm to farm. Symptoms include:

  • Mastitis – often in multiple quarters, with a poor response to treatment
  • Lameness (infected joints) in cows and/or calves
  • Pneumonia in cows and/or calves
  • Swollen heads
  • Ear infections/head tilt in calves
  • Conjunctivitis in calves
  • Death

Cows may be infected with Mycoplasma but not show any symptoms (carrier animals).

Mycoplasma can spread from cow to cow through contact with contaminated milk, nasal secretions or uterine fluid. Semen, embryos and contaminated equipment are also potential sources for transmission.

Calves can become infected by consuming milk from infected cows or contact with infected animals, equipment or surfaces.

There are no effective approved treatments for Mycoplasma. Antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) can be used but animals often respond poorly.  

Disease prevention

Each of these three diseases can be introduced to a farm by an infected animal (or people, vehicles and equipment contaminated with the bacteria). Good biosecurity is essential. Good biosecurity includes:

  • Don’t bring any animal on to your farm until you have established its disease risk. Talk with your vet about what tests can be conducted to eliminate some of the disease risks. For example, Johnes Disease is difficult to test for but the presence of Mycoplasma can be tested through a bulk milk sample from the supplying farm (because Mycoplasma bacteria is shed intermittently in the milk, it is best to conduct the test on more than one occasion).
  • Quarantining and monitoring introduced animals before mixing with other stock.
  • Managing visitors to ensure they don’t bring contaminated clothing or equipment on to your farm. This is very important in the calf shed as calves are particularly vulnerable to diseases.

A good starting point is to develop a biosecurity plan for your farm – and then follow the procedures developed to keep your farm safe. It is also important to communicate your biosecurity plan so everyone (family, staff, visitors) understands that biosecurity is important to your business and what role they play in preventing diseases from entering or spreading on your farm.

There are online resources available to help you develop a biosecurity plan for your farm. Check out for information and resources. Your local vet is also an important resource in helping to identify your farm’s disease risk and help to develop strategies to minimise any risk.

Healthy Calves

The workshop also provided a timely opportunity to discuss calf rearing.

Ensuring cows are in good health and condition is the first step in achieving a healthy calf. Transition cow feeding should start 21 days prior to a cow’s predicted calving date.

Colostral vaccines (e.g. Salmonella, rotavirus) aim to protect the calf from that disease by increasing specific antibodies in the colostrum. These vaccines must be given to the cow at the right time to achieve maximum effectiveness. This typically means giving the booster vaccination six to ten weeks prior to calving start date so the level of antibodies are high when colostrum production starts.

It is then VERY IMPORTANT that calves drink colostrum once they are born, otherwise they won’t get the antibodies and will be at a much higher risk of developing a disease.

Colostral vaccine

Image: Rearing Healthy Calves (Dairy Australia)

The four Q’s of colostrum management

  1. Quickly. The ability of calves to absorb antibodies from colostrum quickly decreases with time. Therefore, calves need to be fed colostrum as soon as possible.
  2. Quality. Ideally, colostrum should be tested using a Brix refractometer. Colostrum with readings greater than 21% is of good quality. Colostrum with readings less than 21% is of poorer quality.
  3. Quantity. The amount of colostrum calves need depends on the quality – the poorer the quality, the more they need. A good rule of thumb is:
  • If you have good quality colostrum, give 2 x 2 litre feeds within the first 12 hours of life
  • If you have poor quality colostrum (or aren’t testing), give 2 x 3 litre feeds within the first 12 hours of life.
  1. sQueaky clean. Make sure all equipment is clean – the bucket you collect colostrum in as well as the stomach tuber, bottle or feeder. This reduces the risk of bacteria being fed to the calf.

After following the 4Qs things become easy(!). Ensure calves have access to fresh, clean water and pellets in addition to their milk. Have a system in place to monitor calf health and identify any calf that isn’t ‘doing well’ so problems can be addressed early.

Bobby calves

Bobby calves need to be managed to ensure good welfare outcomes. If bobby calves are being sold for slaughter, they MUST:

  • be in good health, alert and able to rise from a lying position
  • be protected from cold and heat
  • have been fed milk or milk replacer on the farm within 6 hours of transport
  • not spend more than 12 hours in transport
  • have protection from wind when being transported

The farm also must have an auditable and accessible record system. The records must identify the age of the calf and when the calf was last fed (i.e. within 6 hours of transport).

More details about calf rearing can be found in Dairy Australia’s Rearing Healthy Calves book. This is available at

Happy calving!

Thank you to Colleen Stewart (Scottsdale Veterinary Service), Craig Dwyer (Smithton Veterinary Service) and Grant Rogers (Dairy Systems Pty Ltd) for their assistance with the animal health workshops. Thank you also to the farmers who spoke at the workshops about their calf rearing systems.