Mortalities in bobby calves associated with long distance transport.

OBJECTIVE: To investigate how distance of transportation and time of year affects mortality of bobby calves. METHOD: The overall mortality of bobby calves transported by road to an abattoir in Northern Victoria was investigated by the analysis of mortality data from 1998 to 2000 from the abattoir records. RESULTS: Mortality of bobby calves increased exponentially with distance of transportation to the abattoir. The association between distance travelled and mortality was greatest in August. The increased mortality associated with greater distance travelled occurred during transportation rather than after arrival at the abattoir. The highest mortality of bobby calves was seen in October, followed by September, and the lowest was observed in August. CONCLUSION: Limits on the distance of transportation of bobby calves should be incorporated into future codes of practice to reduce the mortality of bobby calves.

Infection rates in reactors to an absorbed ELISA used in a test and cull program for bovine Johne's disease.

OBJECTIVE: To determine the proportion of cattle, whose sera gave positive reactions in a commercial enzyme linked immunosorbent assay (ELISA) for bovine Johne's disease, that were confirmed infected with Mycobacterium avium subsp paratuberculosis by histology and culture of tissues. PROCEDURE: Dairy cattle (n = 493) from the Echuca district of Victoria, whose sera were positive in the ELISA, were slaughtered at an abattoir where standard specimens were collected for histology and culture. Only if samples were histologically negative were further samples submitted for culture. RESULTS: The proportion of cattle in which infection was confirmed increased from 70.4% in 1996 to 89.4% in 2001 giving an overall confirmation rate of 79.9%. This was mainly because more reactors were confirmed by culture each year, the proportion increasing from 0% in 1997 to 27.5% in 2000 but decreasing to 16.7% in 2001. If all unconfirmed reactors were presumed to be uninfected, the minimum specificity of the ELISA was 99.62%. There were no significant differences between the age groups in the proportion confirmed infected. CONCLUSION: Confirmation rates and specificity of the ELISA were high when used in a typical JD-infected Victorian dairy cattle population. Imperfect sensitivity of histology and culture and the selection of reactors which favoured more false positives, means the estimates were probably conservative. Confirmation rates were not affected by age of ELISA reactor.

The effects of reducing the length of canine teeth in sucking pigs by clipping or grinding.

OBJECTIVE: To provide production data that would support or discount current teeth clipping practices in sucking pigs. DESIGN: Intervention study of 207 litters of pigs on a commercial farm. PROCEDURE: Litters were assigned to one of three interventions undertaken at 1 day of age: clipped using hand-operated side cutter pliers, ground using a battery-operated grinder or left intact. The effects of the intervention on weaning weight, preweaning mortality, facial lesions, gum damage and arthritis in litters of pigs were recorded, as was the incidence of udder damage of the sows. Weight gain and facial damage postweaning of pigs within each intervention group were recorded. The cost:benefit of each intervention was determined. RESULTS: Average weaning weight of pigs whose teeth were clipped was higher than of those whose teeth were ground but not of those with intact teeth. Clipping resulted in fewer preweaning deaths than both unclipped and ground litters due to fewer overlays. The incidence and severity of face scarring was higher in unclipped litters than clipped and ground litters. Treatment had no effect on face scars at weaning, udder damage, post-treatment fostering, time of preweaning deaths or postweaning weight gain. There was an additional labour cost of 6 cents per pig with teeth clipping. CONCLUSION: This study supports teeth clipping of sucking pigs because there are welfare, production and financial benefits including reduced facial damage and preweaning mortality.

Estimate of the sensitivity of an ELISA used to detect Johne's disease in Victorian dairy cattle herds.

OBJECTIVE: To estimate the sensitivity of the ELISA used in dairy cattle herds participating in the Victorian Bovine Johne's Disease Test and Control Program (TCP). PROCEDURE: The percentage of ELISA reactors in age and test cohorts was estimated from age-specific test data derived from TCP herds with long testing histories. Age-distribution data from production-tested herds enabled estimation of reactor rates in animals that were culled or died. RESULTS: ELISA sensitivities at the first test round in herds achieving five, six and seven annual herd tests were 16.1, 14.9 and 13.5% respectively. The ELISA sensitivity in 2, 3 and 4-year-old animals at the first test round in herds testing seven times was 1.2, 8.9 and 11.6% respectively but remained between 20 and 30% in older age-groups. CONCLUSION: The sensitivity of the ELISA is considerably lower than previous estimates, probably because previous estimates were predominantly measured against faecal culture, which has subsequently been shown to have low sensitivity itself, and did not appreciate the long period that appears to precede detectable faecal excretion in most animals.

Resistance to macrocyclic lactone anthelmintics and associated risk factors on sheep farms in the lower North Island of New Zealand.

AIM: To estimate the prevalence of resistance to macrocyclic lactone (ML) anthelmintics over a 3-year period on sheep farms in the Taihape area, and to determine associations between the presence of ML resistance and farm management practices. METHODS: All farmers with >1,000 lambing ewes served by one veterinary practice in the Taihape area of the central North Island of New Zealand were invited to take part in the study (n=157); respondents were selected on their willingness to participate. Resistance to ML was measured during 2004-2006, using a standard faecal egg count reduction test (FECRT) and a half dose of oral ivermectin (IVM; 0.1 mg/kg; n=84). Additional FECRTs were conducted separately on some farms, using full doses of IVM (n=47), levamisole (LEV; n=49), a benzimidazole (BZ; n=76), and a BZ/LEV combination (n=42). Resistance was defined as <95% faecal nematode egg count reduction (FECR) 7-10 days post-treatment. Larval cultures were performed on pooled faecal samples from all pre- and post-treatment groups for which any positive faecal nematode egg counts (FEC) were recorded. To ascertain whether particular management or drenching strategies were associated with the presence of resistance, a questionnaire comprising 50 questions was developed, and each farmer interviewed individually. RESULTS: Of all farmers invited, 84/157 (54%) participated in this study. Based on undifferentiated FEC, ML resistance to the half-dose IVM was evident on 46/84 (55%) participating farms. The majority of these cases (71%) involved Ostertagia (Teladorsagia) circumcincta. Resistance was also evident to full doses of IVM on 22/47 (47%), BZ on 41/76 (54%), LEV on 18/49 (37%), and BZ/LEV on 2/42 (5%) farms. Positive associations (p<0.05) were evident between the presence of ML resistance and management practices, such as: weaning over half of the lambs onto paddocks not grazed by lambing ewes since June; not always returning lambs to the same paddock after drenching; and the use of visual signs to assess 'worminess'. Measuring drench efficacy in January to March rather than later in the year, and presence of resistance to BZ or LEV were associated with a higher apparent prevalence of ML resistance (p<0.05). CONCLUSIONS: Anthelmintic resistance, and particularly ML resistance, was widespread on sheep farms in the Taihape area, and mostly involved O. circumcincta. The prevalence of resistance was lower on farms on which management practices, particularly those involving lambs, maintained refugia of unselected nematodes. Further investigation is required to develop control strategies which minimise selection for resistant worms, and how these may vary with climate.

Evidence that moxidectin is a greater risk factor than ivermectin in the development of resistance to macrocyclic lactones by Ostertagia spp in sheep in south eastern Australia.

AIM: To determine associations between resistance of Ostertagia (=Teladorsagia) spp to macrocyclic lactone (ML) anthelmintics and history of use of anthelmintics, by type, on commercial sheep farms in temperate regions of southern South Australia and Victoria, Australia. METHODS: Faecal egg count reduction tests (FECRTs) were conducted during a 2.5-year period (from August 2001 to January 2004) and records of the type of anthelmintic used in the 5 years preceding the FECRTs were collected from commercial sheep farms (n=103) in southern South Australia and Victoria, and data analysed retrospectively. ML resistance was defined as <95% reduction of Ostertagia spp 10-14 days after treatment with ivermectin (IVM), orally, at half the manufacturer's recommended dose rate. Use of anthelmintics in the preceding 5 and 10 years on each property was classified according to the nett number of years each of the following classes of drug had been used: IVM oral liquid (IVO), IVM controlled-release capsules (CRCs), abamectin (ABA), moxidectin (MOX) or a non-ML anthelmintic. The prevalence of ML resistance, by property, was analysed for associations with prior use of anthelmintics. RESULTS: Resistance by Ostertagia spp to ML anthelmintics was evident on 51/103 (49.5%) properties. The prevalence of resistance was lowest (23%) on properties on which MOX had not been used, and was significantly higher (64-77%) on properties on which MOX had been used for > or =2 of the preceding 5 years (p<0.001). In contrast, the prevalence of resistance was highest (70-74%) on the properties on which IVM, or IVM and/ or ABA, had not been used in the previous 5 years (on which the use of MOX was predominant), and was markedly lower (20- 42%) on properties that had used IVM or IVM and/or ABA for at least one of the preceding 5 years. Prevalence of resistance was higher for properties on which the only ML anthelmintic used was MOX (19/29=66%) than for those on which the only ML used was IVO (2/19=11%; p<0.001). Properties on which the only ML used was MOX were 2.72 times more likely to have resistance than properties on which the only ML used was IVO (95% confidence interval (CI) = 1.01-5.08). CONCLUSION: Use of MOX for > or =2 of the preceding 5 years was associated with a higher prevalence of resistance to ML by Ostertagia spp on sheep farms in south eastern Australia than the use of IVO.