Health strategies for prevention and treatment of calf diarrhoea

Diarrhoea is the most common disease in young calves, accounting for about 50% of all calf deaths and significant financial losses on both beef and dairy enterprises. The disease can be easily recognised, and it is important that treatment is administered rapidly to maximise the chance of survival.

Equally important, however, is a thorough understanding of the underlying causes of the disease and the implementation of appropriate management steps to minimise the impact of the disease in the future. This article discusses key strategies for management and prevention of neonatal diarrhoea, and how vets can engage with their clients on this disease.

Diarrhoea can result from a number of different infectious and non-infectious causes and, in the absence of diagnostic testing, it is not possible to predict the specific cause based on clinical presentation alone. Determining the cause of a scour outbreak is important, as it may indicate future lines of prevention and may show any potential zoonotic risks. A wide range of calf enteric pathogens include viruses, bacteria and protozoa, and a plethora of commercially available packages are on offer to assist in identifying pathogens in diarrhoeic calves.

Patient-side lateral flow immunoassays for rotavirus, coronavirus, Cryptosporidium parvum and K99-positive Escherichia coli offer a useful tool to identify some common scour pathogens, and are great for client engagement in diagnostics. They should be used alongside other testing modalities, such as bacteriology and microscopy, to provide a complete picture.

As with any diagnostic investigation, it is important to select animals with representative clinical signs for sampling and to interpret results in light of the clinical picture.

Treatment and early management

Scouring calves should be isolated from other animals in the group, and clients should be advised on the correct procedures to minimise the potential for spread of disease.

Treatment of diarrhoea in calves should have four goals: correction of dehydration and electrolyte abnormalities, correction of acid-base abnormalities, provision of nutrition, and treatment of the underlying infection. The leading cause of mortality in affected calves is dehydration and electrolyte disturbance.

It follows that the backbone of routine therapeutics should be fluid and electrolyte replacement that is custom-designed on the clinical signs exhibited by a particular affected individual. Antimicrobials and antiprotozoals are best used sparingly and only when a specific indication is present.

Oral fluid therapy is the mainstay of most treatment protocols for neonatal calf diarrhoea and is widely adopted because it is cheap and easy to administer on farm, and success rates can be very good if it is instituted early in the course of the disease.

While vets are often not directly involved in the administration of oral electrolytes, it is important they work with their clients to ensure farm staff can correctly identify when fluids are required and put in place robust protocols that detail the appropriate products and quantities.

One of the most common challenges on farm is people underestimating the quantity of electrolytes required to address even the slightest dehydration; this can be addressed through client education and easy-to-follow health protocols. Within any health protocols put in place on farm, it is also important that it is clear when veterinary assistance should be sought; in the case of diarrhoeic calves, this will be in part due to the requirement for IV fluid therapy.

IV fluid therapy is indicated in cases of severe dehydration (greater than 8%) or in situations where the calf is exhibiting signs of CNS depression, weakness, inability to stand and an absent suckle reflex. In practice, the rapid use of IV fluids can be an extremely useful tool in the treatment of calf diarrhoea, and they can be used to restore an animal to a state where it can take oral fluids.

It is important not to underestimate the amount of fluid required. The fluid deficit in litres should be estimated as percentage dehydration times bodyweight in kilogrammes. Ongoing losses should also be estimated and added to the deficit, as should daily maintenance of 50mL/kg/d to 100mL/kg/d. It is beyond the scope of this article to provide an in-depth review of IV fluid therapy, but as a general rule diarrhoeic calves are typically acidotic, so alkalinising fluids, such as 0.9% saline or Ringer’s, are recommended. Calves may also benefit from exogenous bicarbonate administration.

Use of antimicrobials in the treatment of calf diarrhoea is controversial. Given the potential for the use of antimicrobials to promote antimicrobial resistance in both pathogenic and commensal bacteria, we should ensure we use and prescribe them prudently.

Calves with diarrhoea frequently have small intestinal overgrowth with E coli bacteria, regardless of the inciting cause, and 20% to 30% of systemically ill calves will have a bacteraemia (Fecteau et al, 1997; Lofstedt et al, 1999). Use of antimicrobials is, therefore, indicated only in systemically ill animals and should be focused against E coli and potentially Salmonella species.

As diarrhoea can be accompanied by intestinal cramping and abdominal pain, the use of analgesics is indicated. NSAIDs decrease inflammation in the gastrointestinal tract and reduce the effects of the endotoxaemia and septicaemia. Treated calves also have improved starter ration intakes, a higher bodyweight gain and increased activity level (Todd et al, 2007).

No specific therapies are available for the treatment of viral infections, and so treatment in cases of rotavirus and coronavirus should be based on supportive fluid therapy. Control of viral diarrhoea can be effectively achieved through a combination of good husbandry practices and the use of vaccination in cows prior to calving, to increase the quantities of virus-specific antibodies in the colostrum. Use of diagnostics to identify parasitic causes of diarrhoea enables the appropriate antiparasitic to be prescribed as required.

Control and prevention

Whatever the causative organism, common approaches to husbandry and management are likely to reduce calf scour incidence. Approaches can be divided into maintenance of disease resistance, reducing infection exposure and good feeding practices.

In the neonatal calf, the biggest single determinant of immune status will be colostrum feeding. The effectiveness of natural immunity depends on the quality, volume and timing of colostrum received.

Veterinary surgeons can help producers develop programmes to routinely monitor colostrum management, and to ensure the effectiveness of colostrum feeding. Colostrum feeding practices should also always be looked at as part of any investigation into neonatal disease. When assessing colostrum feeding, it is important to ensure the system in place is providing sufficient quantity of good quality colostrum as quickly as possible.

Following birth, the ability of the calf’s gut to absorb the Igs rapidly decreases, and by 24 hours it is unable to absorb them at all. It is, therefore, important to ensure colostrum is fed as soon as possible after birth.

A critical mass of 100g to 200g of Ig must be ingested by a newborn calf to acquire passive immunity. In dairy cattle, this level of Ig intake requires 3L or 4L of good quality colostrum. Left to suckle on their own, most dairy calves will fail to ingest sufficient mass of Ig, so it is often necessary to hand feed or administer colostrum via an oesophageal feeder.

Quality of colostrum will vary from cow to cow. While ensuring proper feeding and dry cow management is important to ensuring good-quality colostrum, a number of other factors will also influence colostrum quality. Ill animals, such as those suffering from mastitis or milk fever, will produce poorer quality of colostrum.

Passive immunity in calves is evaluated or quantified by measuring serum or plasma IgG or serum total protein within the first seven days. Historically, the individual calf standard for categorising calves with successful passive transfer or failure of passive transfer of immunity was based on serum IgG concentrations of more than or equal to 10g/L and less than 10g/L, respectively.

This dichotomous cut-off was based on higher mortality rates in calves with serum IgG of less than 10g/L. An alternative four-step categorisation has been proposed to enable better farm level monitoring of the transfer of passive immunity (Lombard et al, 2020). As serum IgG concentrations are not practical for on-farm implementation, the authors provide corresponding serum total protein and percentage Brix values for use as part of on-farm monitoring programmes (Table 1).

Table 1. Consensus serum IgG concentrations and equivalent total protein (TP) and Brix measurements, and percentage of calves recommended in each transfer of passive immunity (TPI) category (Lombard 2020).
TPI category	Serum IgG category (g/L)	Equivalent TP (g/dL)	Equivalent % Brix	Recommended percentage of calves tested (% calves)
Excellent	≥25.0	≥6.2	≥9.4	>40
Good	18.0-24.9	5.8-6.1	8.9-9.3	~30
Fair	10.0-17.9	5.1-5.7	8.1-8.8	~20
Poor	<10.0	<5.1	<8.1	<10

Use of serum total protein monitoring offers a simple way of monitoring colostrum feeding practices on farm and can be a key component of calf-health monitoring programmes or disease investigations. The system proposed by Lombard et al (2020) gives clear categorisation of passive immune transfer, but its cut-offs are based on calves fed natural colostrum.

Lopez et al (2021) highlights the potential for serum total proteins to be less well correlated with serum IgG and the tendency for calves fed colostrum replacer to have lower serum total proteins, even when they have adequate serum IgG. So, if implementing monitoring systems on farms where colostrum replacers are being used, it is important to potentially reduce the target thresholds.

Good hygiene must start from the moment the calf is born, as many infections are picked up from the calving area. Hygiene and cleanliness must then be maintained throughout the calf-rearing period, with specific care being taken to clean and disinfect feeding equipment between feeds, and to thoroughly clean and disinfect the environment on regular occasions, and between batches of calves.

For calves being fed on artificial systems, it is important any disease investigation examines all feeding processes. Digestive disorders can result from irregular feeding, changes in the temperature of the milk replacer, incorrect positioning of buckets or artificial teats. One of the most common issues identified is variation in concentration resulting either from human error during preparation, or from issues with calibration on automatic feeding systems.

Conclusion

Calf diarrhoea is a multifactorial disease, and the rapid implementation of appropriate therapy is essential for a rapid recovery. Vets should work with their clients to ensure the economic impact of this disease can be reduced, through the rapid management of outbreaks and the implementation of good husbandry practices and appropriate control measures.