An NCD outbreak is usually the result of a combination of adverse environmental conditions, poor calf immunity and the increased presence of one of the many infectious agents. Producers therefore need to assess potential risk factors at a herd level before implementing a preventative management strategy. 

MAIN CAUSES

NCD mainly affects calves less than six weeks old, although calves up to four months of age can be affected. Treating affected calves is time consuming and even if they survive, their growth rate is usually compromised. However survivors may have the advantage of developing some immunity to future outbreaks.

Rotavirus and cryptosporidia are the most common pathogens associated with NCD in beef calves in southern Australia. The other major pathogens are enterotoxigenic E. coli (ETEC), salmonella and coronavirus, and less commonly, coccidia, yersinia and clostridia. 

Many of these pathogens have zoonotic potential, so appropriate precautions should be taken when handling and treating scouring calves. 

MINIMISING RISK

The main ways to reduce the susceptibility of a herd to NCD are to minimise the exposure of at-risk calves to pathogens, and to promote calf immunity. In management terms, these aims are best achieved by:

• Targeting a short joining period (such as 60 days) to limit the age range of calves and lower pathogen levels
• Ensuring cows calve in a body condition score of 2.5-3.5 and are supplemented with trace minerals if necessary
• Calving heifers and cows separately, and drifting out cow/calf units into nursery paddocks as soon as possible
• Starting a new nursery group every three weeks and not merging groups until the youngest calf is six weeks old
• Selecting calving and nursery paddocks that are well-sheltered and well-drained
• Preparing selected calving and nursery paddocks by spelling or grazing with low-risk stock (weaners, dry stock or sheep) for at least three months prior
• Using different paddocks each year and not one in which NCD has occurred within 12 months
• Preferably watering stock out of non-leaky troughs rather than dams
• Avoiding manure build-up by frequently moving feeding sites, putting gravel or woodchips around troughs and if muddy, scattering 1kg lime per square metre around them weekly 

Heifers' calves are the most susceptible to NCD as heifers generally have poorer mothering ability, lower colostrum quality and an increased risk of dystocia. They are often calved down in greater stock densities to make monitoring easier, but this also increases the pathogen load in the paddock. 

To further minimise the risk of NCD in both heifers' calves and them main breeding herd, ensure calves are receiving adequate colostrum immediately after birth. If additional colostrum is required, such as after an assisted birth, this is best sourced from other cows on the home property. Colostrum can be frozen and thawed for later use.

OTHER TACTICS

Salmonella may be introduced onto a property by contaminated feed or water, infected livestock (especially cows during calving) or other animals and birds. The bacteria can survive in the environment for several years. To minimise the risk of NCD associated with salmonellosis, avoid mixing calving cows with recently introduced livestock or stressors such as droving, inadequate nutrition or rapid changes in diet. 

Enterotoxigenic E. coli (ETEC) is the most common strain of this naturally-occurring bacteria to cause NCD. Calves are only susceptible to ETEC during the first 14 days of life (with peak risk in the first three days) so should have minimal exposure to faeces during this time. A vaccine is available for herds with recurring diagnosed ETEC.

IDENTIFYING AND OUTBREAK

If a NCD outbreak occurs in your herd, it is important to initially analyse the affected mob in situ to try and identify predisposing management factors. These could include environmental stresses and areas where pathogens may have built up in the calving paddock, feed available in the paddock, the body condition of cows and calves and the age range of calves in the affected herd. 

Also note whether there has been much dystocia in the herd and any biosecurity risks such as newly introduced livestock or a watercourse through the paddock that originates on another property. Avoid mustering the mob to examine or collect samples from calves as this will increase stress and risk of disease transmission.

Next determine the age of the calves affected and the proportion of calves in the following four groups:

• Unaffected,
• Scouring but still suckling, bright and alert (can't catch),
• Scouring and slightly dehydrated (can catch with some effort),
• Scouring and significantly dehydrated (easy to catch or collapsed)

Table 1 shows symptoms and possible diagnoses for scouring calves. Your local veterinarian will help with a more accurate assessment of sick animals, and can arrange for faecal, serum, blood or liver samples from affected calves to be tested for full diagnosis. 

TAKING CONTROL 

The main aims of control measures implemented in herds with NCD are to protect unaffected calves from infection, isolate the infected mob, minimise transmission within the affected mob and minimise the spread of zoonotic pathogens to humans.

There is a vaccine available to prevent ETEC infections in calves. It is only likely to be beneficial to vaccinate previously unvaccinated, pregnant cows in the face of an ETEC outbreak if the outbreak occurs at the beginning of calving. Two injections three weeks apart are required, and will be of most benefit when given to cows at least 10 days off calving. There is also a salmonella available in Australia, but it efficacy is yet to be proven.

For most herds fighting undiagnosed NCD pathogens, isolation is the most effective way to protect unaffected calves. Separate infected and non-affected mobs until all calves are six weeks or older, and if handling is required, yard unaffected calves first.

Next try to minimise the transmission of infection within the affected mob. If less than 10% of calves in the herd are affected, isolate scouring calves and their dams if practical. If more than 10% are affected, be prepared for a high number of the remaining animals to develop clinical disease or to already be sub-clinically affected.

Fence off heavily used calf camps and water courses or dams in affected paddocks and treat wet areas with lime. Delay stressful management procedures (such as calf marking, weaning and transport) for as long as practical. 

Be aware of zoonotic pathogens being transmitted to humans when handling and treating affected calves. Wear overalls and disposable gloves and keep contaminated clothing away from family members.

TIMELY TREATMENT

Once the cause of a NCD outbreak has been diagnosed (and even whilst waiting for a conclusive diagnosis), the treatment given to individual calves will depend on factors such as whether the calf is still suckling, how dehydrated it is, how badly it is scouring and the risk or evidence of septicaemia. 

A vet will advise of treatment options but they will usually involve administering electrolyte solutions, either orally using an oesophageal feeder or as part of intravenous fluid therapy. 

An antimicrobial may also be administered, and the calf may or may not be left with the dam, depending on the severity of the infection and symptoms. An excellent decision tree to determine the appropriate treatment of a scouring calf is available on page 23 of the MLA publication Diarrhoea in Beef Herds (see More Information). 

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