THE RAIN and cooler weather has arrived in many dairying regions of Australia and while these changing conditions have been welcomed by most dairy farmers, cool wet weather also favours the survival and proliferation of many calf scour pathogens.
In seasonal parts of the country, the weather changes also coincide with calving and the incidence of calf scours tends to increase with this change in climate.
This article discusses Escherichia coli (E.coli), a relatively common cause of neonatal calf diarrhoea.
What is E.coli and how is it spread?
E.coli are bacteria shed in the faeces of infected calves and carrier cows.
These calves and cows may appear clinically normal but they are an important source of infection and contribute to environmental contamination with the organism.
Each infected animal excretes many more bacteria than it originally ingested, creating a ‘multiplier effect’, leading to a progressively contaminated environment over time.
E. coli can survive in soil for more than 6 months and in water for at least 3 months.
Spread of the organism is by the faeco-oral route and is associated with a contaminated calving environment, infrequent collection of calves from the calving environment, a dirty calf trailer and poor calf shed hygiene.
How does E.coli cause disease?
There are two major syndromes associated with E.coli infection in calves.
The first is enterotoxigenic E. coli (ETEC) and affects calves < 4 days of age.
The second syndrome is enterohaemorrhagic E. coli (EHEC) and usually occurs in calves older than 6 weeks of age. The remainder of this article will focus specifically on ETEC.
E. coli causes diarrhoea in young calves by evading many of the body’s defence mechanisms to fight disease.
These include: the ability to survive the acidic environment of the abomasum; the ability to attack and grow in the small intestine; and the ability to produce toxins that directly cause diarrhoea by the increased secretion of water into the intestine.
E. coli are cleverly designed in that they can attach to the intestinal wall by specific receptors on their surface.
This means they cannot easily be removed by the usual defence mechanisms of the body.
However, they only have this ability for the first 48 hours of a calf’s life, after which the intestine of the calf is no longer susceptible to E.coli.
This means that the disease typically occurs over the first 4 days of life. A common scenario is calves being brought in from the calving area, already showing signs of scour.
The faeces of affected calves is generally yellow/white, extremely watery, foul-smelling and may resemble ‘pipe-stream’ diarrhoea.
Defaecation tends to be effortless with the faeces appearing to flow out of the anus of affected animals.
Calves may appear weak, lethargic and unwilling to drink even before the onset of diarrhoea.
Dehydration, observed as sunken eyes and a dry nose may become severe as the diseases progresses.
Calves in the terminal stages of disease may be unable to stand, lying flat-out or appear to be comatose.
Death can occur within a few hours, some calves being found dead without any previous signs. Other calves may survive for 3 to 5 days before succumbing to this disease.
How can E.coli be prevented?
Prevention of calf diarrhoea relies upon:
1. Reducing the risk of exposure to harmful scour-causing pathogens
Reducing the risk of exposure involves minimising the faecal contamination in the environment and reducing the time period that susceptible calves spend in that environment.
This refers to the calving area, calf trailer and calf shed.
At least twice daily collection of calves from the calving area, rotation of calving paddocks with a suitable stocking rate, good calf trailer and shed hygiene will help minimise the risk of infection to E.coli.
2. Increasing the resistance to disease by the calf
Adequate intake of colostrum provides some protection against E.coli but may not prevent diarrhoea entirely.
Failure of passive transfer of protective antibodies from colostrum is a significant risk factor for E.coli infection in calves.
Active feeding (by teat or tube feeder) a known volume of the best quality colostrum available as soon as possible after birth will help provide protective immunity.
Excellent hygiene during the collection, storage and handling processes is essential to reduce the risk of bacterial overgrowth.
Colostral vaccines can also be used in adult cows to boost specific colostral antibodies to E.coli. The timing of these vaccines is critical and is important to always read the manufacturer’s specific vaccination schedule.
It is essential to get an accurate and prompt diagnosis when dealing with calf scours, not only to appropriately treat affected calves but to establish preventative health measures for future calving periods.
• Gemma Chuck is an adviser with Apiam Animal Health.