Diarrhoea, or calf scours, is the most common problem seen in young dairy calves. Farms experiencing sickness in more than 10% of calves or deaths before weaning of more than 3% should seek advice from a veterinarian.
Many causes of calf scours can be passed onto humans, particularly children, so it is important to maintain good personal hygiene whenever handling sick calves.
More information about calf scours can be found in Chapter 7 of Rearing Healthy Calves.
What to look for
- Diarrhoea, which can be evident on the tail and/or down the back legs. The consistency and volume can vary from profuse, watery diarrhoea to mucoid with or without blood
- Varying degrees of dullness, lethargy and disinterest in feed. Slow or incomplete milk feeding is often an early sign of sickness and these calves should be closely monitored
- Sunken eyes caused by dehydration
- Droopy ears
- Dry nose
- Reduced or absent 'suck reflex'. This can be tested by inserting a gloved finger into the calf's mouth. In a normal calf, this should initiate reflex sucking
- Some causes of calf scours may also result in sudden death
The most common infectious causes of calf scours include:
- Viruses such as rotavirus and bovine coronavirus
- Bacteria such as Salmonella species and E. coli
- Parasites such as Cryptosporidium (“Crypto”) or Coccidia (coccidiosis)
Calves become infected with these calf scour 'pathogens' via feed or water contaminated with manure or by direct ingestion of manure. This could be from licking walls, consuming milk or colostrum contaminated with manure and chewing contaminated bedding.
Digestive upsets due to changes in milk volume, quality, milk composition or temperature variations can also cause calf scours. This form of scours (milk scours or nutritional scours) is usually mild and calves remain bright and alert. However, if such changes occur when calf scour pathogens are also present, the stress of changing the diet can cause an outbreak of infectious diarrhoea.
Calves should have a consistent diet from birth to help reduce the risk of calf scours.
Animals likely to be affected
Calves are susceptible to the various causes of calf scours at different ages, which are outlined in the timetable below.
Confirming the diagnosis
A general diagnosis of calf scours is made by observation of diarrhoea in a young calf. However, it is important to determine the actual cause of calf scours to ensure the most appropriate treatment and to help with future prevention strategies.
Some treatments are very specific to the cause and an accurate diagnosis will help ensure the correct treatment in a cost-effective and timely manner. Specific calf scour pathogens can be diagnosed by submitting a manure sample to a veterinary clinic or by conducting a calf-side test using a special test kit.
It is essential manure samples are taken from untreated calves to give the best possible chance of getting an accurate and representative diagnosis. Laboratory tests can also check the susceptibility of any bacteria pathogens that are present to different antibiotic treatments.
Giving oral electrolytes to correct and prevent dehydration is the most important aspect of calf scours treatment. Scouring calves require six to 10 litres of fluids per day divided over at least 2–3 feeds. This total fluid requirement includes any milk feeds.
Scouring calves having difficulty standing or are unable to stand up, have sunken eyes, no suck reflex, feel cold and have a dry, sticky mouth require urgent veterinary attention or should be humanely euthanased.
Should I stop feeding milk?
Milk feeding of scouring calves should never be stopped for more than 24 hours as electrolytes do not contain enough nutritional value to sustain the calf.
Most veterinarians will recommend continuing milk feeding but in more frequent, smaller feeds. Sometimes withholding milk can reduce the calf scours and re-introducing milk can cause recurrence of scours again. It is important to remember that the gut of a scouring calf is damaged and needs time to heal, which is generally more than 24 hours.
Although re-introduction of milk can cause scours to recur, the nutrients provided in milk are essential for the calf to recover. All signs that the calf is recovering should be considered, such as willingness to feed and general attitude, as well as the presence/absence of diarrhoea.
With the vast majority of oral electrolytes, it is important to ensure at least two hours has elapsed between feeding electrolytes and milk and to never mix electrolyte powders into milk. This causes interference with formation of the milk clot within the calf’s stomach, which is critical for correct digestion. Always check the manufacturers instructions on how to administer electrolytes as the volume and mix rates are highly variable.
Antibiotics are only effective against bacteria. They have no effect on viruses or parasites and will not correct dehydration. As such, antibiotics should only be used in scouring calves if:
- Laboratory or calf-side tests indicate pathogenic bacteria such as E. coli or Salmonella have been diagnosed
- There is blood in the faeces, suggestive of severe damage to the gut
- The calf is very depressed, weak or unable to stand, suggestive of toxins (produced by pathogenic bacteria) present in the blood
If a veterinarian prescribes antibiotics, it is essential the correct dose is given by the correct route for the correct duration. Clear records of all treatments should be kept, noting the calf ID, dates of treatment, nature of treatment and outcome. All treated calves should be clearly identified and designated feeding equipment used. Sick calves should be fed and treated last.
Blanket use of antibiotics or medicating large groups of calves should be avoided whenever possible and only ever done under the advice of a veterinarian.
Antibiotics and other veterinary drugs should be stored in a secure cupboard or the fridge (depending on the specific drug), out of the reach of children. All staff responsible for administering veterinary drugs should ensure they are adequately trained in this procedure.
Fresh, clean water should be available to calves from birth, ensuring even very young calves can reach the water source. Scouring calves can become very dehydrated between milk feedings and will feel thirsty and drink water to help combat the effects of dehydration.
- Inadequate colostrum intake (quantity, quality, timeliness, cleanliness)
- Poor feeding hygiene, such as poor storage and handling of milk or contaminated feeders
- Inconsistent feeding routines (type, volume, temperature of milk feed)
- Poor housing management, such as continuous flow vs all-in all-out system
- Inadequate housing, such as wet bedding, poor ventilation, build-up of manure or a dirty calf trailer
- Overcrowding or mixing of calves of different ages
- Stress, such as disbudding, weaning, vaccination, turnout or transport
- Poor biosecurity, such as inadequate separation of sick calves
Prevention of calf scours can be achieved by addressing the above risk factors. Good management alone will reduce the risk of calf scours significantly.
Colostral vaccines are available for calf scour pathogens. These involve priming the immune system of the cow to boost specific antibodies in colostrum which is then fed to the calf. The effectiveness of colostral vaccines relies on calves receiving adequate colostrum in the first 24 hours of life.
Typically, cows are vaccinated 10 to 12 weeks before calving followed by a second dose four to six weeks later. An annual booster is then given four to six weeks before calving. Label instructions should always be followed when administering colostral vaccines as the exact vaccination schedules can vary for each product.
More information about ensuring adequate colostrum intake and preventing calf scours can be found in the Rearing Healthy Calves manual.
Causes of scouring in older calves
What to look for
- Mucus or bloody diarrhoea, often in many animals within a group
- Straining to defecate (signs include a raised tail and arched back)
- Staining of the tail, hocks and hindquarters with dark-coloured diarrhoea
- Calves may also have weight loss, be depressed, off-feed and dehydrated
Coccidiosis is caused by ingestion of the eggs of a parasite called Eimeria. These eggs can survive for a long periods –about two years – in the environment, especially in wet, dark conditions. Infections tend to be opportunistic, often triggered by stressful events such as weaning, turnout or poor weather. Infection is from direct ingestion of Eimeria eggs from contaminated pasture or bedding and contaminated troughs or feeders.
Animals likely to be affected
Coccidiosis will most likely affect calves from one to 12 months of age. The severity of the infection is directly related to the number of eggs ingested. It is estimated that approximately 95% of coccidial infections are subclinical, meaning animals do not show any obvious signs of disease. A reduction in growth rates may be the only sign with these mild infections. However, severe debilitating disease can result when many eggs are ingested from a heavily contaminated environment.
Coccidiosis is diagnosed in the laboratory by examination of a manure sample. It is worth noting that mixed infections are common, with affected animals frequently having high worm burdens and other bacterial infections, such as Yersinia.
In an outbreak, it is ideal to separate healthy calves within a mob from affected calves. This will help reduce the risk of unaffected calves contacting the manure of infected calves. However, animal which appear healthy may be subclinically affected and should be closely monitored for further signs of disease.
Treatment is targeted and specific to coccidiosis which means an accurate diagnosis is essential prior to any treatments. Again, this is especially important in mixed infections.
Oral or intravenous fluid therapy under the supervision of a vet may also be required if the animal is severely dehydrated. Affected animals may have a prolonged recovery and have permanent ill-thrift.
- Exposure to the Eimeria parasite in contaminated environments, such as paddocks used for calves year after year
- Stress, such as poor weaning regimen, high stocking density, transport or multiple husbandry procedures
- Poor nutrition, such as low availability or inconsistent intake and lack of coccidiostat in feed
- Poor pasture management, such as lack of paddock rotation and younger age groups following older age groups
- Exposure to Bovine Viral Diarrhoea Virus (BVDV)
Coccidiosis may be prevented by:
- Addressing the risk factors above
- Implementing a rotational grazing strategy to reduce the exposure of calves to coccidial oocysts
- Avoiding the use of the same paddocks for calf rearing year-on-year if possible
- Avoiding later groups of calves being exposed to the same pasture as earlier groups of calves. During high risk periods, by the time the later calves are turned out, the environment is already very contaminated
- Adding monensin or laslocid to supplementary feed during high risk periods
What to look for
- Poor growth rates in young stock
- Poor body condition and ill-thrift, such as a rough, dull coat
The most important gastrointestinal worms of dairy calves include:
- Ostertagia osteragi (small brown stomach worm)
- Trichostronylus axei (stomach hair worm)
- Cooperia spp. (small intestinal worm)
In northern and subtropical dairying regions, Haemonchus placei (barber’s pole worm) can also be problematic.
Animals likely to be affected
Dairy calves are mostly affected by gastrointestinal worms from weaning until 12 to 15 months of age. After this time, calves develop a strong age-related immunity to gastrointestinal worms. Older animals are rarely affected unless there is underlying stress that causes a breakdown of immunity.
Confirming the diagnosis
Gastrointestinal worms can be diagnosed in young animals by conducting laboratory examination of manure samples, called faecal egg counts. Often larval culture is also required to help interpret the faecal egg counts according to the mix of worm species present. Individual faecal egg counts of 150 to 250 eggs per gram, depending on larval culture results, may indicate treatment is required. A veterinarian will be able to guide interpretation of results relevant to the area.
Pooled faecal egg counts are not recommended as there can be considerable variation in egg counts between calves within a group.
Treatment of gastrointestinal worms involves the use of anti-parasitic drenches. There are several drenches available which fall into one of the four classes:
- Mectins, such as Dectomax®, Cydectin® or Ivomec®
- White drenches, such as Panacur®
- Clear drenches, such as Nilverm®
- Combinations, such as Trifecta® or Eclipse®
Research conducted in Victoria between 2013 and 2016 found a high level of resistance to available drenches on dairy farms. Therefore, it is recommended faecal egg counts are done on manure samples at the time of treatment and 10 to 14 days after treatment to check the drench is working.
- Always treat the heaviest in the mob and check weights using scales or a weigh tape
- Always check drenching equipment is calibrated by squirting the desired volume into a measuring cylinder
- Only treat when required and regularly monitor faecal egg counts
- Wherever possible, use short acting oral drenches and combinations rather than single-active drenches
There is no clear evidence to support the routine treatment of adult dairy cows for gastrointestinal worms. Some international and small Australian studies demonstrated milk production responses to treatment, but this was unable to be replicated in several other studies.
A research project supported by Dairy Australia is currently underway in south-west Victoria and aims to provide clearer guidance as to whether treatment is required and when it is best administered, such as dry off or calving time.
- Exposure to the parasites in highly contaminated environments, such as paddocks used for calves year after year
- Stress, such as weaning or high stocking density
- Poor nutrition
- Exposure to BVDV
- Higher levels of parasites on pasture in late autumn, winter and early spring.
Problems with gastrointestinal worms can be prevented by:
- Providing good nutrition (see Heifers on Target resources)
- Implementing an appropriate rotational grazing strategy to avoid use of the same paddocks for calf rearing year-on-year if possible
- Regularly monitoring faecal egg counts