Al Vizard

Principles for the use of macrocyclic lactones to minimise selection for resistance

OBJECTIVE To provide principles for the appropriate use of avermectin/milbemycin or macrocyclic lactone (ML) anthelmintics in sheep, to ensure effective worm control and to minimise selection for ML resistance. STRATEGY The principles were based on an assessment of the information currently available. The MLs were categorised into three groups (ivermectin [IVM], abamectin [ABA] and moxidectin [MOX]) based on structural differences, persistence and efficacy against ML resistant strains. The reported order of activity or efficacy against ML resistant worm strains was IVM<ABA<MOX. General treatment schemes were considered for Australian conditions and were divided into the following situations: 1. quarantine treatment, 2. treatment on/to clean pasture, 3. treatment on/to safe pasture, 4. treatment on/to moderate/heavily contaminated pasture. For each of these situations a strategy was considered for farms where ML resistance was present or absent. It was assumed that resistance commonly occurs in some or all other broad spectrum anthelmintics, and even where ML resistance has been detected, the ML group remains the most effective. The guidelines provided are general and it is expected that state agencies and sheep/veterinary advisers would give specific advice to suit their environments and drug resistance/worm problems. CONCLUSIONS The primary recommendation is to use a mixture of effective drugs when treating sheep. However, unless the combination treatment is highly effective it is unlikely to delay selection for ML resistance if sheep are being treated and moved to a clean or safe pasture. Where possible, reliance on the ML anthelmintics should be reduced by not using them every year, not using them in low risk stock or by using narrow spectrum and low efficacy drugs such as naphthalophos when appropriate. Anthelmintic treatment should be given as part of a strategic worm control program. It is suggested that IVM-oral and IVM-capsules should not be used when ML resistance is present. In this situation MOX or ABA should be used in combination with other drugs, provided that the chosen ML is effective against the resistant parasite. It is essential to monitor the efficacy of ML and drug combinations by post-treatment worm egg counts, particularly when ML resistance has been detected.

Determination of the optimum cut-off value of a diagnostic test

Abstract Many diagnostic tests require the determination of cut-off values that discriminate uninfected from infected individuals. The cut-off values of a serodiagnostic test were calculated to minimize the total cost of misdiagnoses. Three different assumptions were made about the density distributions of the uninfected and infected populations to which the test was to be applied: (1) the population distributions were identical to the sample distributions; (2) both populations were normally distributed; (3) the population distributions may not be normal but may follow other density distributions that are used commonly. The cut-off values calculated using each assumption varied considerably. This indicates that accurate estimations of the density distributions of the populations are required to determine the optimum cut-off values. There is often insufficient information to estimate population density distributions adequately. Decisions regarding cut-off values of diagnostic tests should be reviewed as more data become available.

Verification and value of the Australian Bureau of Meteorology township seasonal rainfall forecasts in Australia, 1997–2005

We verified the Bureau of Meteorologys seasonal rainfall forecasts for 262 townships throughout Australia, from its inception in June 1997 to May 2005. The results indicate that the forecasting system had low skill. Brier Skill Score and the receiver operating characteristic values were uniformly close to the no skill value. Forecast variances were consistently small. The overall observed variance was 0.0048, 2.1% of the variance of a perfect system. The estimate of the gradient of the outcome against forecast was 0.42 and was imprecise. Definitive statements about bias cannot be made. The value of the forecasts for decision-makers was estimated using value score curves, calculated for six forecast scenarios. All curves indicated that no economic benefit could have been reliably derived by users of the seasonal rainfall forecasts, with the exception of users with decisions triggered by a small shift in the forecast from climatology, in which case small economic gains may have occurred. Small value scores were associated with the observed forecast variance, not the observed bias. We examined the expected change in value scores associated with any future increase in forecast variance. This showed that a moderate increase from the observed variance would bring limited benefits. Substantial value to a broad range of users will only occur with a large increase in forecast variance. To deliver this, new lead indicators with markedly better predictive characteristics may need to be developed for the seasonal rainfall forecasting system. Copyright

The resolution and potential value of Australian seasonal rainfall forecasts based on the five phases of the Southern Oscillation Index

We assess the resolution of the Southern Oscillation Index (SOI) seasonal rainfall forecasting system and calculate the loss in potential value of the forecasting system using a cost/loss model. Forecasts of the probability of a ‘dry’ autumn, winter, spring, and summer were obtained for 226 towns across Australia, based on the 5 phases of the SOI. For every town the variance ratio, the observed forecast variance as a proportion of the variance of a perfect forecasting system, was calculated for each season. Value score curves, showing the expected value of the forecasts as a proportion of the expected value of perfect information, were calculated for every town for each season. Maps of variance ratio and maps of mean value scores across Australia were produced by ordinary kriging. In all seasons and regions the SOI forecasting system had a variance ratio of less than 0.20, indicating that resolution and skill were never high. Variance ratios greater than 0.10 only occurred in parts of south-eastern Australia and the Cape York region during spring and in the Townsville region during summer. The variance ratio was less than 0.05 for the majority of Australia during autumn, winter, and summer. The mean value scores for actions that are only triggered by a large shift in the forecast from climatology were uniformly close to zero in all seasons and regions, indicating that little or no value can be derived in such cases. Actions triggered by a moderate shift of the forecast were also generally associated with low value scores. Mean value scores above 0.20 were limited to actions with a decision threshold close to climatology and only occurred in parts of south-eastern Australia and the Cape York region during spring and in the Townsville region during summer. We conclude that the imperfect resolution of the SOI forecasting system has a substantial effect on potential value. The forecasting system can potentially deliver value to users with actions that are triggered by a small shift in the forecast from climatology, especially in eastern Australia during spring, but not to users with actions that are only triggered by a large shift of the forecasts from climatology.

High-quality care improves outcome in recumbent dairy cattle.

OBJECTIVE To investigate the influence of the quality of care on outcome and occurrence of secondary damage in recumbent dairy cows. METHODS Recumbent dairy cows were monitored during their recumbency under field conditions in South Gippsland, Victoria, Australia. The cause of the original recumbency of 218 downer cows was determined and any secondary damage, day 7 status, final outcome and the nursing conditions of the cows were recorded. A four-tiered grading system describing nursing quality was developed to allow analysis of its influence on outcome and on the occurrence of secondary damage. RESULTS Day 7 outcome, final outcome and occurrence of important secondary damage were very strongly associated with the level of overall care provided to the recumbent cows. There was a decrease in the percentage of cows recovering by day 7 from 33% to 0%, a decrease from 45% to 0% of cows eventually recovering and an increase from 68% to 100% of cows with clinically important secondary damage as overall care decreased. CONCLUSION Management of recumbent cattle is potentially a significant animal welfare issue for the dairy industry and their care is a very important but often under-appreciated aspect of their management. Recovery is positively influenced by high-quality care by improving the chances of recovery from the initial cause of recumbency and by reducing the occurrence of secondary damage. Recumbent cows must either be nursed at a high level of care or euthanased promptly.

IDENTIFICATION AND PREVALENCE OF ERRORS AFFECTING THE QUALITY OF RADIOGRAPHS SUBMITTED TO AUSTRALIAN THOROUGHBRED YEARLING SALE REPOSITORIES

We aimed to identify common mistakes made when radiographing yearling sale horses. Radiographic examinations from repositories at eight yearling sales held in Australia in 2003 were assessed by one of four veterinary radiology specialists. Each radiographic examination consisted of a maximum of 34 radiographs. Each radiograph was assessed for errors associated with movement, exposure, positioning, labeling or marker placement, and processing, and categorized as either ideal, less than ideal or nondiagnostic. In addition, from the first 800 sets catalogued, 167 were selected randomly and read twice by the four radiologists for agreement analysis. A total of 81,297 radiographs were examined for errors affecting quality. Positioning errors were the most common reason for radiographs to be considered nondiagnostic (2432/81,297; 3%), with the flexed lateromedial (LM) metacarpophalangeal joint, LM metatarsophalangeal joint, and the dorsomedial palmarolateral (DMPaLO) carpal views being the most frequently involved. Overexposure (14,357/81,297; 17.7%) was the most common reason for radiographs being categorized as less than ideal with the LM stifle view the most represented. Agreement within and between radiologists for reporting errors in positioning of the flexed LM metacarpophalangeal joint, LM metatarsophalangeal joint, and DMPaLO carpal views varied from slight to almost perfect. The low repeatability within radiologists on some views suggests that before declaring a radiograph nondiagnostic it is worth considering rereading it at another time. Care should be taken in positioning of the flexed LM metacarpophalangeal, LM metatarsophalangeal, and DMPaLO carpus views to maximize radiograph quality.

Importance of secondary damage in downer cows.

OBJECTIVE To investigate the relative importance in downer cows of the primary cause of recumbency in comparison with secondary complications. METHODS Downer dairy cows were monitored during their recumbency under field conditions in South Gippsland, Victoria, Australia. The cause of the original recumbency of the 218 cows was determined and secondary damage, status on day 7 and final outcome were recorded. RESULTS Some type of secondary damage was found in 183/218 (84%) cows, of which 173/218 (79%) had damage deemed to be clinically important. By day 7, 52 (24%) had recovered and 69 (32%) eventually recovered. Of the 149 (68%) cows that were euthanased or died, 23 (15%) were deemed to have been lost solely from the primary cause, 107 (72%) from secondary damage and 19 (13%) from a combination of both. CONCLUSION There was no difference in recovery among the five broad groups of causes of primary recumbency. Secondary damage was very common and presented in a large variety of ways, with many cows having multiple types of secondary damage concurrently. For most cows the secondary damage was more important than the initial primary damage in determining their fate.

Association between the purchase price of Thoroughbred yearlings and their performance during the 2- and 3-year-old racing seasons

OBJECTIVES Describe the association between the purchase price of Thoroughbred yearlings sold in Australia and racing performance as 2- and 3-year-olds. METHODS Race performance data of 2773 Thoroughbred yearlings sold at auction during 2003 were collected. Associations between purchase price and the probability of starting, the number of race starts and the prize money earned were examined. RESULTS In total, 2206 (79.6%) horses started a race. The mean number of race starts was six and the mean prize money earned was A

A model to estimate the economic value of using individual fleece fibre diameter measurements to class wool

24,420. A total of 1711 (61.5%) horses earned prize money, 402 (14.4%) earned more than their purchase price, 312 (11.2%) earned more than A

An assessment of intra- and interobserver agreement of reporting orthopaedic findings on presale radiographs of Thoroughbred yearlings.

40,000, the estimated cost of training, and 142 (5.1%) earned A