Impact of infectious diseases on beef cattle reproduction

P.D. Kirkland, G. Fordyce, R. Holroyd, J. Taylor and M. McGowan - NSW Dept of Primary Industries, Qld Dept of Primary Industries and University of Qld - Meat & Livestock Australia

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

This research article covers the impact of infectious diseases on beef cattle reproduction, in particular, minimise the spread of pestivirus and reduce losses in Australian herds.

What is the problem?

The profitability of a beef breeding enterprise relies heavily on the efficiency of reproduction. A cow may be considered to be inefficient if it fails to produce a marketable calf at regular intervals, ideally each year.

Task Objectives:

1. To lay it out the failure associated with pestivirus and Neospora infections through case studies in beef breeding herds over a range of management systems and environments;

2. To determine positives transmission rates in large extensive herds by the strategic monitoring of groups of cattle where active infection was occurring;

3. To represent the meeting of key infectious diseases on reproduction in beef herds and carry out an economic analysis of those impacts.

What did the research involve?

As the aim of the project was to study the impact of the target agents in herds that were representative of the pastoral beef industry of Eastern Australia, an emphasis was placed on the selection of herds from New South Wales and Queensland but herds from Victoria were also included.

3.1 Selection of project herds
-The field studies consisted of a series of case studies and intensive investigations of herds that were spread across Eastern Australia and, to establish virus transmission rates in large extensive herds, were complimented by serological monitoring of several herds in which active infection was occurring.

3.1.1 Herds in New South Wales and Victoria
-Herds in NSW and Vic with reproductive loss identified at any point from joining through to weaning (or in one instance, as yearlings) were recruited.

3.1.2 Herds in Queensland
– In the extensive herds of the Central and North Queensland pastoral regions, diagnostic investigations are undertaken less frequently.

3.1.3 Serological surveys and diagnostic data
-Since late 2006, Pfizer Animal Health has been encouraging veterinarians and producers to establish the pestivirus status of breeding cattle.

3.2 Field methods

3.2.1 Servicing veterinarians
-In NSW and Victoria, all herds were examined and sampled by the private veterinary practitioner who was normally engaged by the owner.

3.2.2 Collection of baseline data
-The specific observations, measurements and sampling that were undertaken varied depending on the nature of the herd, owner co-operation and facilities available.

3.2.3 Reproductive assessments and herd health monitoring
– In NSW and Victoria, herds were currently experiencing a pestivirus problem or had affected animals, indicating that there had recently been infection in the herd.

3.3 Virus transmission studies

3.3.1 Herd selection
-A number of herds were initially screened to determine whether there was likely to be active virus transmission in the herd.

3.3.2 Herd Monitoring
-Herds were monitored for periods ranging between 2 and 11 months. Blood samples were collected at the start and end of the monitoring period for testing for pestivirus antibodies and for detection of persistently infected animals.

3.4 Laboratory methods

3.4.1 Participating laboratories
-The laboratory aspects of this project were restricted to 2 laboratories. Samples from the herds in NSW and Victoria were tested at EMAI while the samples from the Queensland herds were submitted to the DPI & F veterinary laboratory at Toowoomba.

3.4.2 Bovine viral diarrhoea virus
-The principal test for antibodies to BVDV was the agar gel immunodiffusion (AGID) test. If additional testing was required to confirm the status of an animal, the virus neutralisation test was used.

3.4.3 Neospora caninum
-Antibodies to Neospora caninum were detected using an indirect ELISA developed at EMAI.

3.4.4 Other pathogens
-Testing for the detection of Campylobacter foetus, leptospires and Tritrichomonas venerealis utilised standard diagnostic procedures. Microagglutination tests were used to test for antibodies to L. hardjo and L. pomona.

3.5 Economic modelling and assessment

3.5.1 Methodology – Queensland
-The intention was to assess economic impacts of both pestivirus and Neospora, firstly by establishing representative models of herd production systems in tropical Queensland, and then by altering model inputs to match the potential ranges of the effects of these diseases .

3.5.2 Methodology – New South Wales and Victoria
-In NSW and Victoria, the intention was to use an established economic model for pestivirus (P. Holmes, unpublished), based on an ‘average’ 250 breeding cow self-replacing herd in southern Australia.

3.6 Additional sources of data
-In order to place the findings of this project in the context of the national beef herd, data were also analysed from a pestivirus surveillance project sponsored by Pfizer Animal Health, Australia.

What were the key findings?

4.1 Participating Herds

4.1.1 NSW/Victoria
-In NSW 6 herds were studied in detail. There were 2 small herds (1,000 breeders). In Victoria there were 2 herds, 1 small and the other a large study.

4.1.2 Queensland
-There were 13 herds recruited for reproductive monitoring in Queensland. Ten of these were large herds (>500 cows), 2 herds were medium sized (250-500 cows) and there was 1 small herd.

4.2 Pestivirus and Neospora status of project herds

4.2.1 Herds with an identified problem (NSW & Vic)
-The serological status of the herds in NSW and Victoria that had been recruited because of a known pestivirus problem is summarised.

4.2.2 Herds of unknown status (Qld)
-Although none of herds in Queensland, with one possible exception, had a proven pestivirus or Neospora problem, the serological status of representative groups of cattle had been established at the start of the project.

4.3 Reproductive performance

4.3.1 Impact of pestivirus
-Each of the 8 herds studied in NSW and Victoria experienced losses of varying degrees as a result of pestivirus infection in the breeding herd.

4.3.2 Impact of Neospora caninum
-The prevalence of infection with N. caninum in herds in both NSW and Victoria was found to be very low, ranging from 1% to 4%.

4.3.3 Impact of other pathogens
-The herds studied in this project were specifically selected either as a result of an identified disease problem associated with pestivirus infection or were herds where there was potential for losses due to pestivirus or Neospora infections.

4.4 Pestivirus transmission in extensive herds
-In the 3 large Queensland herds where groups of cattle were specifically selected for study, the rates of pestivirus transmission ranged from 9-26% per month.

4.5 Economic assessments

4.5.1 NSW and Victorian herds
-The financial loss in these herds could not be determined because it was not possible to access the full herd production data and financial records.

4.5.2 Queensland – Economic modelling
-There was little evidence of pestivirus or Neospora impact during this study.

4.6 National prevalence of pestivirus infection

4.6.1 Pestivirus serology
-Results were available for serological profiles of 336 herds across all Australian states.

4.6.2 Detection of persistently infected cattle
-Persistently infected animals were detected in 354 new herds during 2007 &. As these were herds for which samples had been submitted because of a disease investigation, they represent only a small proportion of the total number of herds with PI animals.

4.7 Discussion
-The original project proposal allowed for the study of 6 herds in NSW & Victoria and 8 herds in Queensland.

4.7.1 Impact of pestivirus
– In NSW and Victoria, presenting problems at the time that herds were first investigated ranged from abortions detected at pregnancy testing, the birth of congenitally deformed calves through to the sudden deaths of cattle up to 18 months of age.

4.7.2 Pestivirus transmission
-In the 3 large Queensland herds where groups of cattle were specifically selected for study, the rates of pestivirus transmission were sufficiently high to probably produce an immune heifer population by the time animals reach breeding age.

4.7.3 National significance of pestivirus
-The finding of evidence of active or recent infection with pestivirus in more than 60% of the herds involved in the serological profiling is consistent with past estimates.
With such a high proportion of susceptible animals in these herds, the likelihood of a casual introduction of the virus establishing and spreading becomes much higher.

a) within the herd where the virus is endemic in one mob but not another and infection occurs when animals are moved between groups. There were several examples of this in the NSW herds and there were a number of examples in the serological profiling where one age group was fully susceptible and yet there was clear evidence of active infection in another.

b) neighbouring properties as a result of ‘over the fence’ contact or as a result of animals straying;

c) other introductions such as the purchase of new stock;

d) infection when animals are moved to another property on agistment as a result of drought. Agistment can also create susceptible groups when they are segregated from an endemic source of infection.

4.7.4 Impact of Neospora caninum
-The prevalence of infection with N. caninum in herds in both NSW and Victoria was found to be very low, ranging from 1% to 4%.

4.7.5 Impact of other pathogens
-There was little evidence of losses associated with other reproductive pathogens, with perhaps low losses due to leptospirosis in 2 herd herds (one in NSW, one in Qld) and Campylobacter in 2 Queensland herds.

Final comment

There is a commitment to yield recomending material that does not have a direct link with the supplier of a commercial product that is promoted for pestivirus control. MLA and state Departments of Primary Industries could play a major role in this effort.

2012 - Australia - P.D. Kirkland, G. Fordyce, R. Holroyd, J. Taylor and M. McGowan - NSW Dept of Primary Industries, Qld Dept of Primary Industries and University of Qld - Meat & Livestock Australia
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