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This article was published in 1975
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Scours in Calves

I. Littlejohns, B.V.Sc., Veterinary Research Station, Glenfield.

Over the past decade there has been a generally increasing recognition of scours in calves, particularly in beef production, as an emerging problem. As specimens submitted to Glenfield for investigation of problems under this general heading came from a wide variety of field circumstances, an attempt was made to define the condition or conditions which were of most importance. This was mainly done by the issuing of a questionnaire, of which a copy was to be completed for each property known to experience a problem of calf scours. The questionnaire survey had three main purposes,

1). to define the problem or problems

2). to determine facts which might indicate aetiology and,

3). to select a property or properties which experienced the problem in typical form, and which were suitable ones in other respects on which to undertake more intensive investigations.

The response to the questionnaire survey was poor, 30 returns being received over the year 1974. No returns at all were received from two areas which are generally reputed to be severely affected.

What has been extracted from the 30 returns is summarised under headings of general, indicative, unforeseen and difficulties.

I GENERAL

1. About 50% of the returns were concerned with substantial problems. The other 50% described rather casual events of minor consequence.

2. Returns were received from the following Pastures Protection Districts, in the numbers indicated.

Mudgee	11
Glen Innes	3
Forbes	33
Maitland	2
Albury	2
Molong	2
Bathurst	1
Coonabarabran	1
Carcoar	1
Bombala	1
Casino	1
Goulburn	1
Gundagai	1

The results are unbelievable as a reflection of the area incidence and must reflect primarily the attention given to the survey by officers in the different areas.

3. Types of cattle which made up affected herds were,

beef	25
mixed	4
dairy	1

Again, the result is unbelievable as a reflection of a general incidence pattern and it would seem that the survey has commonly been taken to be one concerned particularly with beef production. Perhaps the problem has existed for so long in dairy areas that it has ceased to be news. Also in dairy areas, it is probably more commonly attributed, rightly or wrongly, to poor nutrition or hygiene.

4. 27 of 30 returns described the problem as becoming evident since 1968. It would not be clear, however, whether this indicates an emerging problem or simply more response from those currently and recently affected.

5. Health of stock after being affected by scours has been rated as,

good	14
fair	9
poor	6
no opinion	1

This determination is highly subjective and has to be related to various individual expectations. It is also confused by graziers being variously satisfied by responses to treatment.

6. Duration of the disease has been described as from 2 days up to 28 days on different returns and is very variable. Note that the two returns which deal with confirmed orbivirus scours are in the higher range. One might then query whether the shorter duration events are: a). other conditions, or b). determined by other qualifying circumstances.

II INDICATIVE

1. Pink eye was listed as a concurrent disease in 8/30 returns. This is an association which could not be regarded as causative but may reflect common factors e.g. fly activity, of consequence in epidemiology.

2. Good, lush pasture was very commonly described as being associated with the clinical event. This might suggest that nutritional factors can contribute to the clinical manifestation.

3. 14 out of 30 returns associated the disease with hot, humid conditions of spring and summer. The spring / summer incidence might be thought to be determined by the calving season but 5 returns dealt with herds which calve all year round and these described seasonal incidence of scours as,

September - December	( Forbes )
November - January	( Molong )
July - November	( Mudgee )
*November - April	( Maitland )
*October - December	( Casino )
* are the two returns which relate to herds in which orbivirus infection has been confirmed.

Also, single claims that

a). early spring calves are not affected,

b). July-September calving is preventive.

III UNFORESEEN

1. A number of returns referred to losses which would have been experienced if treatment or management had not been implemented to avoid them. As other replies then related to the supposed happy state of disease control it may be that there was information available which was not included in the return.

2 One return of particular interest referred to a 100% incidence in first calf heifers. This could be taken as a strong indication of an infectious disease to which cows had their immunity boosted at or after their first calving.

IV DIFFICULTIES

A number of problems have arisen in extracting results from the returns. They are considered as they reflect on information obtained to date and so that they might be avoided in further investigations.

1. Mortality has frequently been expressed as a percentage of the morbidity. The base against which a mortality rate is determined must be established and both morbidity and mortality should be related to the total number at risk.

2. Operator bias seems to have been affecting some returns. e.g., depilation of the thighs was described in 4 returns - all by one operator.

3. A number of returns were completed by owners who have not always understood the question or the answer alternatives. e.g. 'Mo super' appears not to have been properly interpreted.

4. A number of returns were incomprehensible in part, either from being frankly illegible or from including nonsense replies e.g., 'calving April-July with 3 - 4 week old calves being affected in November-January'.

5. As indicated in I,1., about 50% of the returns seemed to describe inconsequential problems, e.g. 2-3 affected out of 120 calves. These respondents might be considered to be obliging malingerers.

6. The occurrence of relapses might be taken as an indication of whether or not the disease is due to an infectious agent which is affected by an immune response.

The summary of questionnaire returns indicates.

Relapses	11
?	7
No relapses	12

It is not clear whether this result indicates 2 or more different conditions or whether it reflects a difference between groups which have or have not been effectively treated. Effective treatment may reduce the immune response and leave the animal open to relapse or repeat infection.

In summary there has probably been more learnt about questionnaire technique than about calf scours. If the information is still worth pursuing then the questionnaire should be redesigned and implemented more purposefully so that the returns depend less on, and the information derived reflects less, personal motivation. One reason against pursuing the questionnaire survey is that the poor response in 1974 was due, in at least some areas, to genuine difficulties experienced by local field staff in giving the time to the purpose rather than to other competing commitments. The situation is not likely to improve so there is no point in setting up a survey which cannot be carried out for lack of time and staff. Also, since the survey was planned, work elsewhere, which has been applied to some extent in this State, has gone a long way towards defining specific conditions which may cause calf scours. Finally, at least one suitable property on which detailed or intensive investigations of the condition which has emerged as a major component can be conducted, has been selected from information obtained from ordinary diagnostic accessions. Perhaps any further survey would have to be justified on the basis of, and directed towards, an undiagnosed calf scours problem if such is substantial after presently recognised entities are eliminated.

VIRAL ENTITIES CAUSING CALF SCOURS.

In New South Wales the agents which are potential causes of calf scours are orbivirus (reo-like), coronavirus, adenovirus and the virus of mucosal disease.

1. Orbivirus.

The classification of this virus has not been finally decided and orbivirus is used as a term of convenience. It will probably not be finally recognised as such. It, or the related viruses in humans and mice, have also been referred to as reovirus - like, totavirus and duovirus.

The orbivirus is the most common viral agent associated with calf scours and is conventionally reputed to affect calves in the first few days of life and to induce a moderate primary disease of short (24 hours or so) duration. The calf is then held to be more susceptible to complicating secondary infections, primarily bacterial e.g., Escherichia coli, Providencia stuartii, which induce more serious and prolonged disease. In practice, experience in this state is that the orbivirus is found well outside the age and clinical duration limits usually proposed. Thus it has been found in calves of several weeks of age, some of which have been at least according to owners, affected for most of that time. Although there are some contrary reports, it is generally true that, with present techniques, the virus will not be demonstrable in the absence of diarrhoea. Diagnosis may be achieved by electron microscopy (E.M.) of preparations from faeces or by immunofluorescent (I.F.) staining of faecal or gut material. The I.F. staining has not been diagnostically useful in N.S.W., probably largely because of the requirements, that the specimens we collected within the first 4-6 hours of scouring and that material be frozen or cold-acetone fixed virtually immediately, are almost prohibitive under field circumstances. Therefore practical diagnosis depends on E.M. of faecal extracts. Facilities are available whereby this can be undertaken, but not without some handicap due to their being geographically remote. A moderate degree of decomposition does not preclude E.M. diagnosis as the virus is quite robust and some decomposition aids its release from tissue fragments.

Vaccination by oral administration of an attenuated virus at birth is practiced in America. However, as the virus is rarely adaptable to cell culture then the availability of a similar, locally derived vaccine could not be foreshadowed. Also, the need to administer vaccine very early in life may not be acceptable within local husbandry methods.

Although maternal immunity does not appear to be important in the natural history of the disease, there appears to be some protection given to calves by hyperimmunisation of the dams. Also, there is some suggestion that susceptibility of the calf is enhanced if the first feed is delayed or restricted. Hence management which favours early and adequate suckling is desirable to counter the effects of the virus.

2. Coronavirus

This agent has been recognised and is manipulated for diagnosis by much the same means as have been applied to the orbivirus. It was initially recognised in herds where orbivirus vaccination was ineffectual and the manifestation of coronavirus infection differs mainly from that due to orbivirus in that older calves, in the first few weeks of life, are mainly affected.

This virus has been demonstrated by E.M. in Victoria but not yet confirmed in N.S.W. Use of I.P. staining is less practicable because samples of gut tissue rather than faeces are said to be usually necessary so that it has little potential for specimens obtained from living animals.

3. Adenovirus

Two subgroups, which include about 10 serotypes, of bovine adenovirus occur. The serotypes vary somewhat in their pathogenic properties. Some have a predilection for endothelial cells of blood vessels of the gastrointestinal tract and are then associated with enteric disease. The serotypes credited with this situation have not been recovered in Australia but the typical histological picture has been seen and the typical adenovirus inclusions are virtually diagnostic.

Adenovirus infection can be expected in older calves, from several weeks to months of age and has been suggested to occur as a herd event consequent upon activation of latent infection in cows. Concurrent respiratory disease commonly occurs.

Diagnosis may be by E.M. demonstration of virus in faeces, by virus isolation in cell culture or by demonstration of new serum antibody in affected animals. None of the methods is reliable or diagnostically certain and other information, including that derived from histopathology would be required to aid diagnosis.

4. Virus of mucosal disease

This virus has been used to induce diarrhoea in neonatal calves experimentally. There is little evidence to suggest that this occurs naturally but occasionally typical sporadic progressive mucosal disease (M.D.) does occur in baby calves. Although not recognised in Australia, the possibility that the 'virus diarrhoea' type of syndrome due to M.D. virus could occur in calves cannot be excluded.

One could not expect to demonstrate virus in faeces by E.M. but isolation in cell culture can be attempted from blood, faeces or any other suitable source. Techniques for the recovery and identification of this virus are well developed at Glenfield, so its recovery offers no real difficulty. Difficulty is more likely to come from picking the manner in which virus is likely to occur in a different form of disease, e.g., the persistent viraemia which occurs in typical M.D. should not be expected nor the more benign forms such as transient enteritis. In these circumstances then, recourse to serological means of diagnosis may be contemplated.

NON-VIRAL SCOURS

Detailed consideration of non-viral infectious agents causing calf scours will not be attempted but it should be noted that bacteria, ranging from highly pathogenic Salmonellae to the more modest strains of Esch. coli, as well as acting alone, are also important as agents which complicate primary viral disease, or even co-operate with the viral agents to generate pathogenic effects.

DIVERSIFYING FACTORS.

In the overall appraisal and diagnosis of viral scours in calves, there are a number of things which should be kept in mind as factors which may produce a picture which is rather different on one occasion than that seen or described, due to the same agent, on another.

Thus, different manifestation of specific infectious disease may result from difference in;

1. Virus strain, due to antigenic differences which may be distinct or partially related and able to induce "heterotypic" or "recall" immune responses; or due to non-antigenic differences such as virulence, stability etc., which can effect the clinico-epidemiological pattern of disease.

2. Host factors, such as age, breed and sex, and their distributions in both donor and receptor animals.

3. Other infectious agents which may variously compete, interfere, complicate or co-operate.

4. Other non-infectious factors such as nutrition, immunological capability or prior priming, management affecting population density and points of contact, hygiene etc.

The complex situation provided by all of the variables in the circumstances under which specific diseases may occur allows that there should be a great deal of variation in the final overall result. Such variation is seen in practice and specific diseases can be expected to cover a rather broader spectrum of manifestation and occur under a wider variety of circumstances than classical description might suggest.