Epidemiological studies of pig diseases: 1. Use of French protocols for risk factor assessment to predict the health status of Australian herds.

OBJECTIVE: To determine in Australian pig herds the accuracy of French protocols for risk factor assessment. PROCEDURE: Data on health indicators and risk factors were collected for three syndromes, 'pre-weaning diarrhoea', 'post-weaning diarrhoea' and 'respiratory problems', using the French protocols. The protocols were used on 118 occasions in 32 Western Australian pig herds during 3 years (1988 to 1991). RESULTS: There was a wide variation in pre-weaning performance, for example growth rate was 107 to 273 g/day (< 200 g/day in 33% of herds). Respiratory lesions at weaning were associated with poor pre-weaning performance. Post-weaning (21 days after weaning) growth rate was 114 to 408 g/day (< 250 g/day in 54% of herds). In the grower herds, 91% of herds had pneumonia, and growth rate was 439 to 625 g/day (< 550 g/day in 54% of herds). Pleurisy as well as pneumonia was associated with reduced growth rate. The risk factor most closely associated with respiratory health status was air volume per pig. CONCLUSION: Risk factors were most accurate at predicting the health status in post-weaning problems. A weaning weight of at least 7.9 kg and weaning age of 30 days optimised weaner performance. Stocking densities and shed designs providing at least 3 m3 air volume and 0.6 m2 floor space per pig throughout the growing phase should be considered for an improved respiratory health status. Australian pig sheds often do not provide a satisfactory environment for optimum health. The technique of risk factor assessment as an aid to the maintenance of health in pig herds is applicable in Australia, but further research is necessary to determine the most important Australian risk factors.

Epidemiological studies of pig diseases: 2. Post-weaning diarrhoea and performance in Western Australian pigs.

OBJECTIVE: To determine in Australian pig herds the accuracy of French protocols for risk factor assessment of post-weaning diarrhoea and illthrift. PROCEDURE: French protocols for the collection of data on health indicators and risk factors for post-weaning diarrhoea were conducted on 54 batches of weaner pigs from 28 Western Australian pig herds during three years. RESULTS: Large variations in post-weaning performance were found. About one-third of the batches were growing at < 200 g/day during the 3 weeks after weaning, and 54% had growth rates of < 250 g/day. Weaning age and weight of at least 30 days and 7.9 kg, respectively, optimised weaner performance. Other risk factors associated with little post-weaning diarrhoea and good weaner performance were high creep feed intakes, relatively little diarrhoea as suckers, and, contrary to expectations, large temperature fluctuations. CONCLUSION: Overall, the 'predictability' of post-weaning problems as assessed by measurement of risk status, was good. However, the model was less accurate at predicting the performance of a single batch of pigs.

The spread of Corynebacterium pseudotuberculosis infection to unvaccinated and vaccinated sheep.

The decrease in the prevalence of Corynebacterium pseudotuberculosis after two generations of vaccination against the disease it causes, was used to estimate the rate of control of caseous lymphadenitis (CLA). Three groups of 150 sheep, of which 50 in each group were artificially infected with C pseudotuberculosis and 100 in each group were uninfected sheep, were run separately for 40 months and shorn 5 times to promote the spread of CLA. One lot of 50 infected sheep and 2 lots of 100 uninfected sheep were vaccinated against CLA. The rate of spread of CLA was recorded. Sheep vaccinated against CLA and naturally exposed to infection had a 74% lower infection rate than unvaccinated sheep. Sheep vaccinated against CLA and exposed to only vaccinated infected sheep had a 97% lower infection rate. Unvaccinated sheep had a 76% infection rate, with 77% of the transmission occurring at the 4th and 5th shearings, without any discharging CLA abscesses being observed. This study supports the view that in Australian wool producing flocks, CLA spreads mainly from sheep with discharging lung abscesses to sheep with shearing cuts. Vaccinated sheep infected with CLA have 96% fewer lung abscesses compared with unvaccinated infected sheep and are therefore less likely to spread this disease to other sheep.

New infection with Corynebacterium pseudotuberculosis reduces wool production.

The effect of natural Corynebacterium pseudotuberculosis infection on wool production and quality in sheep was examined in light of evidence that artificial C pseudotuberculosis infection causes wool production loss. A toxin ELISA was used to identify sheep that had been infected with C pseudotuberculosis. Greasy and clean fleece weights and fibre diameter were compared in infected and uninfected sheep. C pseudotuberculosis infection caused a 3.8 to 4.8% decrease in greasy wool production and a 4.1 to 6.6% decrease in clean wool production. C pseudotuberculosis infection did not affect fibre diameter. The effects of caseous lymphadenitis (the disease caused by C pseudotuberculosis infection) cause an annual loss of about $17 million in wool production to the Australian wool industry.

Vaccine efficacy for reducing turbinate atrophy and improving growth rate in piggeries with endemic atrophic rhinitis.

Two vaccines, based on formalin-killed whole cells of toxigenic Pasteurella multocida type D and Bordetella bronchiseptica combined with a partially toxoided cell extract of P multocida, were prepared with Freund's incomplete adjuvant (vaccine 1) or by alum precipitation (vaccine 2). Each was tested for safety and efficacy in reducing the severity of nasal turbinate atrophy and improving the growth rate of pigs in three Western Australian commercial piggeries with endemic atrophic rhinitis. In safety experiments with vaccine 1, no adverse clinical effects were observed in vaccinated sows or their progeny. Piglets receiving vaccine 2 showed no injection site abnormalities, pyrexia or turbinate atrophy. In field trials, vaccine 1 significantly reduced the prevalence of moderate to severe nasal turbinate atrophy (Done score 3 to 5) when used in two piggeries (A and B). Progeny from vaccinated sows in piggery B also grew significantly faster than controls. When vaccine 2 was used in piggery A at a later date and in another piggery (C), growth rate was not improved in either piggery and the prevalence of moderate to severe turbinate atrophy was reduced only in piggery C.

The effect of antibody to caseous lymphadenitis in ewes on the efficacy of vaccination in lambs.

The effect of maternal antibody to the toxin of Corynebacterium pseudotuberculosis, produced by caseous lymphadenitis (CLA) in ewes or by vaccinating ewes before lambing, on the efficacy of vaccination against CLA in their lambs was examined. Lambs were allocated to treatments according to either the vaccination history of their dam or level of CLA toxin antibody of their dam. They were vaccinated twice using 2 different inoculation regimes and then artificially infected with CLA organisms. The number of lambs with CLA lesions was assessed at slaughter. In one experiment high levels of CLA toxin antibody activity in ewes were associated with decreased efficacy of CLA vaccination in their lambs, when lambs were vaccinated at 2 and 8 weeks or 8 and 14 weeks of age. In a second experiment the efficacy of lamb vaccination at 8 and 12 weeks, but not at 14 and 18 weeks of age, was decreased. In sheep flocks with a high prevalence of CLA, vaccinating lambs against CLA at less than 10 weeks of age may not produce optimum protection against CLA in lambs. There was no difference in infection rate between lambs from vaccinated and unvaccinated ewes. However, vaccination of lambs at 2 and 8 wks was less effective that vaccination at 8 and 14 weeks, probably due to reduced immunocompetence in young lambs. In sheep flocks where significant numbers of lambs receive their primary vaccination at less than 3 weeks of age vaccination programmes to control CLA in lambs may be less effective.

Survey of internal parasites in Western Australian pig herds. 1. Prevalence.

Between September 1982 and March 1984, 101 Western Australian piggeries with 15 or more sows were surveyed to determine the prevalence of internal parasites and examine the relationship between parasitism and management practices. Faecal samples were collected from 20 pigs in 4 age groups in randomly selected piggeries, and examined for the presence of eggs of helminth parasites and protozoan cysts. Evidence of nematode parasites was found in 79% of piggeries. Sows were more commonly affected than other classes of pigs with worm eggs being found in 68% of herds. Oesophagostomum spp was the most prevalent worm species, being found in pigs from 65% of piggeries and in sows in 60% of herds. Ascaris suum was the most common species of worm found in growing pigs. There was no evidence of infection with either Metastrongylus spp or Strongyloides spp in any of the herds sampled. Oocysts of coccidia were found in pigs from 56% of piggeries and Balantidium coli cysts were detected in pigs from 42% of piggeries sampled.

Survey of internal parasites in Western Australian pig herds. 2. Relationship to anthelmintic usage and parasite control practices.

The housing, management and internal parasite control practices used in piggeries in Western Australia was surveyed by interviewing the owner/manager of 100 randomly selected piggeries. At the time of the interview 20 faecal samples were collected from pigs and examined for evidence of internal parasites. Most herds (80%) in which anthelmintics were used, had evidence of nematode infection. Some pig producers were using an anthelmintic that was ineffective against nematode species present while some herds had nematodes that should have been controlled by the anthelmintic being used. Prevalence of nematode infection was higher in pigs run in paddocks than in pigs housed intensively. Washing sows prior to farrowing was associated with a lower prevalence of nematode infection. The findings suggested that pig producers should ensure that the anthelmintic used is effective against the nematodes present in their pigs. It was concluded that administering anthelmintics as a single dose in the feed may not be the most effective method of deworming pigs.

The effects of caseous lymphadenitis on wool production and bodyweight in young sheep.

Two hundred Merino wether hoggets were used to examine the effect of Corynebacterium pseudotuberculosis infection (caseous lymphadenitis) on wool production and bodyweight. Sheep which were challenged with C. pseudotuberculosis (artificially infected) and not vaccinated against this disease produced 0.20 kg less clean wool than unchallenged controls during the following 12 months. The incidence of sheep with lesions in the group that was vaccinated prior to challenge was 55% lower than in unvaccinated challenged sheep but their wool production was not significantly different from either the controls or the unvaccinated challenged sheep. Vaccinated sheep were also heavier than unvaccinated sheep 12 months after challenge. These results indicate that caseous lymphadenitis infection may reduce wool production.

An evaluation of the efficacy of cordial for preventing post-weaning diarrhoea in pigs.

An evaluation of the efficacy of a commercial crystalline cordial concentrate for preventing post-weaning diarrhoea (PWD) and improving weight gains in pigs following weaning, was carried out in 3 herds using 861 pigs. The incidence of PWD in pigs drinking the cordial was reduced in 2 herds and its severity was reduced in one of these. There was no effect on either incidence or severity in the other herd. The pigs given cordial consumed considerably more water per day and less feed per day than pigs drinking plain water during the 10-day supplementation period. There was no improvement in average daily gain or feed conversion ratio attributable to adding cordial to drinking water in any of the herds. In one herd the growth rate of pigs receiving cordial was actually depressed during the supplementation period. There was no reduction in mortality or in number of treatments given for diarrhoea in pigs receiving cordial.

The role of Corynebacterium pseudotuberculosis lung lesions in the transmission of this bacterium to other sheep.

Five groups of 5 shorn and 5 unshorn caseous lymphadenitis (CLA)-free Merino wether weaners were each placed in feedlot pens with 6 Merino ewes, 2 or more of which had CLA lung lesions but no discharging superficial lesions. The sheep were kept together for 5 months. Twenty-eight per cent of the shorn weaners and 20% of the unshorn weaners developed antibodies to Corynebacterium pseudotuberculosis. At slaughter, 8% of the shorn weaners and 12% of the unshorn weaners had CLA lesions in either lungs, lymph nodes or both. In the absence of contact with CLA-infected ewes, a control group of 5 shorn and 5 unshorn weaners failed to develop antibodies to C. pseudotuberculosis or CLA lesions in the same period. This showed that sheep with CLA abscesses in the lungs but no discharging superficial abscesses were a source of C. pseudotuberculosis infection to other sheep.

Evaluation of an enzyme-linked immunosorbent assay for the detection of Corynebacterium pseudotuberculosis infection in sheep.

Two enzyme-linked immunosorbent assays to measure antibody to the cell wall antigen (C-ELISA) and toxin antigen (T-ELISA) of C. pseudotuberculosis were evaluated on serum from 6 separate groups of sheep. For sheep naturally infected with C. pseudotuberculosis the sensitivity and specificity of the C-ELISA was 76% and 73% respectively and for the T-ELISA 67% and 77% respectively. For sheep slaughtered one year after artificial infection the sensitivity of both tests was greater than or equal to 83% and the specificity greater than or equal to 72%. For sheep slaughtered 4 months after artificial infection the specificity of both tests was less than 30% while the mean sensitivity was 85%. The C-ELISA in conjunction with the T-ELISA detected 92% of sheep with lung lesions.

Isolation of toxigenic Pasteurella multocida from an outbreak of atrophic rhinitis in pigs.

An outbreak of severe atrophic rhinitis is described. A toxigenic strain of P. multocida was isolated from one affected pig. Severe turbinate atrophy was not associated with significantly reduced bodyweight gain in a batch of 34 pigs examined at slaughter. The history of the outbreak suggested that pigs recently introduced from overseas may have been the source of the disease.