Grazier perceptions and management practices for liver fluke control in north eastern NSW, Australia.

A survey of livestock producers (graziers) located in north eastern NSW Australia, collected information on perceptions and management practices for liver fluke control in livestock. The total area farmed by the 161 respondents was 195,600 ha (ranging in size from 4 to 10,522 ha) with cattle and sheep being the dominant livestock enterprises. Overall, 80% of graziers relied exclusively on anthelmintics for liver fluke control and few of these graziers (9%) integrated parasite management (IPM) strategies to reduce disease prevalence. Of those relying on anthelmintic control, triclabendazole (TCBZ) was preferentially chosen by 75% of graziers. Fifty five percent of these graziers used TCBZ in combination with oxfendazole (46%), ivermectin (5%) or abamectin (4%) whilst 45% used TCBZ as a single active ingredient. Thirty eight percent of graziers drenched livestock one or more times per year for liver fluke despite claiming they had no liver fluke or confirmed knowledge of infection. Fifty one percent of graziers based anthelmintic dose on the known weight of the heaviest animal in the herd whilst 43% visually guessed livestock bodyweight to calculate anthelmintic dose. Choice of anthelmintic was predominately based on perceived efficacy (45%) despite very few graziers (2%) having conducted post-treatment fluke egg counts. The majority of graziers (76%) were unsure if they had anthelmintic resistance, 21% claimed they had no resistance whilst 3% of graziers had confirmed resistance. Most graziers (97%) also reported farms were cohabited by kangaroos highlighting additional grazing pressures on-farm. This current survey has revealed that graziers rely on anthelmintics as their primary choice for liver fluke control. Reluctance to adopt IPM strategies and a continued heavy reliance on TCBZ, whilst basing anthelmintic decisions on perception rather than measurement and testing, pose threats for the future control of liver fluke in livestock within this endemic area.

Ecology of the free-living stages of Trichostrongylid parasites of sheep.

The prevalence of gastrointestinal nematodes (GINs) is dictated by environmental conditions which influence the survival, development, and migration rates of the free-living stages. While the faecal pellet is the most important micro-environment for GINs, limited data on the impact of temperature and faecal water content (FWC) on their survival, development, and migration limits accurate prediction of nematode pasture infectivity. This study investigated the impact of temperature and FWC on the dynamics of the free-living stages of T. vitrinus, T. colubriformis and T. circumcincta by incubating faecal samples from sheep harbouring mono-specific infection of the GINs in temperature-controlled incubators at constant temperatures ranging from 0° to 40°C and nominal target FWCs ranging from 0% to 80% for 8 days. The different life cycle stages (eggs, pre-infective larvae, intra-pellet infective larvae and extra-pellet infective larvae) were enumerated each day using a modified McMaster technique. Multiple linear regression analysis was used to assess the impact of environmental effects on the recovery of each life cycle stage. A one-way ANOVA was used to compare the life cycle stage tallies between species. Survival and development of each life cycle stage were elucidated by fitting the obtained experimental data to an existing mathematical model which described the dynamics of the free-living stages of the GIN lifecycle. Development of eggs to infective larvae were only observed at target temperatures of 20 and 30ºC (and some development at 40 °C for T. colubriformis). This study predicted development of a minimum of 1% of eggs to intra-pellet infective larvae at temperature ranges of 9-39, 10-39 and 10-38ºC with optimum development occurring at 23, 23 and 20ºC for T. vitrinus, T. circumcincta and T. colubriformis, respectively. Development of eggs to intra-pellet infective larvae was observed at nominal FWC targets of 20% and above where increasing FWC up to 60% resulted in increased tallies of intra-pellet infective larvae. The model predicted that development of eggs to intra-pellet infective larvae required a minimum FWC of 13%, 16% and 17% for T. circumcincta, T. colubriformis and T. vitrinus respectively with higher FWC requirements for migration out of the faecal pellets. Development of T. circumcincta eggs to infective larvae was slower than the other species with only 33% of the T. circumcincta eggs predicted to develop to infective larvae at its optimum temperature and FWC as compared to 47% for T. vitrinus and 56% for T. colubriformis.

Prevalence and pathology of liver fluke (Fasciola hepatica) in fallow deer (Dama dama).

A survey conducted on fallow deer (n = 79) in northern New South Wales Australia, aimed to ascertain the prevalence and gross pathology of liver fluke. In total, three deer populations were assessed (1 farmed and 2 wild) across 2 sites (site A and B) by conducting total fluke counts in the liver and fluke egg counts in faecal samples. At site A, 16 of 19 farmed deer (84.2 %) and 9 of 20 wild deer (45 %) had active or resolved infections. At site B, 16 of 40 wild deer (40 %) had active or resolved infections. Deer with active infections had low fluke burdens (1-11 fluke) which were in the adult development stage, shedding eggs with faeces (0-121.7 eggs per gram). Liver pathology score did not exceed 3.5 out of 5 with gross pathomorphological lesions predominately confined to the peripheral regions of the left lobe. Farmed deer, confined within a fluky habitat, attained the highest group mean pathology score, with dense fibrosis and concomitant atrophy of the left lobe (site A: farmed - 1.8, wild- 0.6; site B: wild - 0.3). Well-defined fibrotic capsules captured and restricted fluke migration beyond the peripheral region of the left lobe of the liver. The presence of live and dead fluke within the fibrotic capsules confirms the inherent ability of fallow deer to resolve infections. This survey has highlighted the susceptibility of fallow deer to liver fluke within an endemic region. Recurrent exposure, as seen in the farmed deer confined within a fluky habitat, appears to strengthen tissue response in terms of gross pathology and may impede the release of fluke eggs from the liver. Low fluke burdens and limited lesions suggest fallow deer have a strong level of resistance to liver fluke. Nevertheless, within this endemic region, fallow deer are widespread and clearly facilitating the liver fluke life cycle. Further research is warranted to ascertain the impact of fallow deer on disease transmission in livestock production when cohabiting the grazing environment.

Prevalence and gross pathology of liver fluke in macropods cohabiting livestock farms in north eastern NSW, Australia, and diagnosis using cELISA.

Liver fluke (Fasciola hepatica) is a parasite of herbivores including wildlife. Macropods, such as Eastern grey kangaroo (Macropus giganteus) and Common wallaroo (Osphranter robustus), are frequently observed sharing grazing sites with domestic livestock. The impact of Macropods, as reservoirs of infection, on livestock production and risks to cross-species transmission are largely unknown. In Phase 1 of this study, liver and faecal samples were collected from 245 Macropods (181 Eastern grey kangaroos, 64 Common wallaroos) cohabiting livestock farms (n = 7) in the Northern Tablelands regions of New South Wales. Total fluke (TFC) and fluke eggs (FEC) were counted in the liver and faeces, respectively, to assess prevalence. Faecal antigens were also measured using the commercial Bio-X Diagnostic Monoscreen AgELISA Fasciola hepatica kit (cELISA) to assess suitability as a diagnostic tool. In Phase 2, Macropod faecal samples were collected from 60 livestock farms to conduct FEC and assess prevalence by region. Liver fluke was prevalent in 22% of Eastern grey kangaroo and 20% of Common wallaroos with prevalence as high as 45% in the Eastern grey kangaroo. Fluke burdens ranged from 1 to 122 flukes (mean = 9 flukes) with a FEC range of 0-195 eggs per gram (epg) of faeces (mean = 18 epg). Evidence of dead and live flukes trapped within fibrotic capsules confirms the ability of Macropods to resolve infections. cELISA proved highly specific (100%) and sensitive (98%) in liver fluke detection however fibrotic capsules observed in the liver may reduce the correlation of coproantigens with fluke burden. Phase 2 revealed that 27% of livestock farms had Macropods infected with liver fluke. Overall, this study confirmed Eastern grey kangaroo and Common wallaroo are susceptible hosts and potential reservoirs for liver fluke and, monitoring infections in Macropods would assist in livestock disease management.

Kangaroos and liver fluke: The role played in cross-species transmission and drug resistance.

Australian livestock are challenged by liver fluke (Fasciola hepatica) in grazing regions endemic to the intermediate snail host. Liver fluke infests a wide range of herbivores including free-roaming wildlife such as kangaroos (Macropods). The role played by Macropods in cross-species transmission and as vectors for anthelmintic resistance is largely unknown. In Phase 1 of this study, liver fluke of Eastern grey kangaroo (Macropus giganteus Shaw, 1790) origin (Kangaroo isolate) were artificially infected in sheep to confirm establishment and cross-species transmission. In Phase 2, the efficacy of triclabendazole (TCBZ) was assessed in vivo against the Kangaroo isolate to identify any drug resistance. Forty (40) merino sheep were housed in pens and allocated to one of 4 groups (Groups 1-4). Groups 1 and 2 were artificially infected with a TCBZ resistant liver fluke isolate (Oberon) originating from sheep whilst Groups 3 and 4 were infected with the Kangaroo isolate (Phase 1). At 9 weeks post infection (wpi), sheep in Groups 2 and 4 were treated with 10 mg/kg TCBZ (Phase 2). Sheep were subsequently euthanased at 11 wpi to conduct total fluke counts (TFC) in the liver. Faecal samples were collected fortnightly to measure fluke egg counts and coproantigens. Individual blood samples were collected, concurrently with faecal sampling, to monitor haematocrit and plasma proteins levels. Liver fluke of kangaroo origin established to patent infections in sheep with similar establishment and pathogenicity to the Oberon isolate. TCBZ achieved an 86 % reduction in TFC (99.8 % - adult fluke, 0 % - immature fluke) in sheep with the Kangaroo isolate and a 28 % reduction in the Oberon isolate (37 % - adult, 0 % - immature fluke). An 89 % reduction in faecal coproantigens was observed in sheep with the Kangaroo isolate and no reduction in sheep with Oberon. This study confirmed cross-species transmission of liver fluke from a kangaroo to sheep. When cohabiting the livestock grazing environment, kangaroos may act as reservoirs for liver fluke and vectors for drug resistance within liver fluke endemic areas.

Australian surveys on parasite control in sheep between 2003 and 2019 reveal marked regional variation and increasing utilisation of online resources and on-farm biosecurity practices.

Australian Wool Innovation Limited (AWI) commissioned three cross-sectional surveys of sheep producers' sheep parasite control practices over a 15-year period from 2003 to 2018. The aims were to document current sheep parasite incidence and control practices, to measure change in sheep parasite control practices over time and to inform extension messages for sheep industry advisors and sheep farmers. The surveys were conducted in 2004, 2012 and 2019 measuring sheep parasite control practices in the years 2003, 2011 and 2018. The surveys focused on incidence and control of the three major sheep parasite groups; gastrointestinal nematodes, blowflies and lice. The 2003 and 2011 surveys were paper-based and the 2018 survey was accessed via a link to an online survey. This article is the first in a series of four presenting the results of the three surveys and will cover methods, demographics, production systems and general parasite management. Response rates to the surveys declined each year from the peak response rate in 2003 (n = 1365 in 2003; n = 575 in 2011 and n = 354 in 2018). Mean reported rainfall was significantly lower in 2018 (407 mm) than in 2003 (611 mm) and 2011 (650 mm). The demographics of the respondents and their production systems were largely similar between the three surveys for respondent age, median property size, income from wool and sheep meat, proportion of the property area cropped, median sheep dry sheep equivalent (DSEs), ewes as a proportion of the total flock and median cattle DSEs. Month of weaning was more likely to be in summer months for summer dominant rainfall areas and spring for intermediate and winter dominant rainfall areas. There was a marked increase in the proportion of respondents asking for an animal health history when introducing sheep to their flock from 2011 (9%) to 2018 (65%). Similarly, a greater proportion of respondents isolated introduced sheep for at least 2 weeks in 2018 (82%) compared with 2011 (19%). However, there was a decrease in the use of a quarantine lice treatment for introduced sheep from 2011 (50%) to 2018 (21%). Farmers rated themselves, other farmers or member of their staff as most important sources of information on parasite control in both 2011 and 2018. There was a significant increase in the proportion of respondents visiting the ParaBoss suite of websites from 2011 to 2018 confirming their growing importance for information delivery and decision support.

Diarrhoea associated with gastrointestinal parasites in grazing sheep.

Diarrhoea is a common, widespread and frustrating reality for sheep enterprises in most sheep producing regions globally and of particular concern in Australia as the major risk factor for breech flystrike. Parasitic disease has long been recognised as an important factor in diarrhoea in sheep, particularly the gastrointestinal nematodes (Trichostrongylus and Teladorsagia species). This review focuses on the role of parasitic infections in causing diarrhoea in sheep, with emphasis on the epidemiology of diarrhoea outbreaks related to worms and opportunities to manage the risk of diarrhoea outbreaks in sheep related to parasitic infections. Parasitic nematodes damage the gastrointestinal tract via a complex relationship between direct impacts from worms, such as physical changes to the gut mucosa, and indirect effects largely associated with the host response. Diarrhoea associated with large worm burdens is most efficiently managed through integrated parasite management programs. Despite some limitations, measuring faecal worm egg counts remains a mainstay for assessing the contribution of worms to outbreaks of diarrhoea in sheep. Larval hypersensitivity scouring is emerging as a significant cause of worm-related diarrhoea in sheep without large adult worm burdens in some geographic locations. The syndrome describes a heightened inflammatory response to the ingestion of trichostrongylid infective larvae seen in the gut of sheep with diarrhoea, and is most effectively addressed through selecting sheep for low breech soiling ('dag scores'), as worm resistant sheep may show an increased propensity for diarrhoea, even with low rates of larval challenge. Importantly, dag should be considered as a separate trait to WEC in breeding indexes. Outbreaks of diarrhoea in young sheep are often multifactorial, and co-infections with nematodes and other infectious agents associated with diarrhoea are common. This presents challenges for the field investigation of diarrhoea in grazing sheep.

Interaction between the effects of evaporation rate and amount of simulated rainfall on development of the free-living stages of Haemonchus contortus.

A factorial experiment (3 x 4 x 2 x 3) was conducted in programmable incubators to investigate interaction between the effects of rainfall amount, rainfall distribution and evaporation rate on development of Haemonchus contortus to L3. Sheep faeces containing H. contortus eggs were incubated on sterilised soil under variable temperatures typical of summer in the Northern Tablelands of NSW, Australia. Simulated rainfall was applied in 1 of 3 amounts (12, 24 or 32 mm) and 4 distributions (a single event on the day after deposition, or the same total amount split in 2, 3 or 4 equal events over 2, 3 or 4 days, respectively). Samples were incubated at either a Low or High rate of evaporation (Low: 2.1-3.4 mm/day and High: 3.8-6.1 mm/day), and faeces and soil were destructively sampled at 4, 7 and 14 days post-deposition. Recovery of L3 from the soil (extra-pellet L3) increased over time (up to 0.52% at day 14) and with each increment of rainfall (12 mm: <0.01%; 24 mm: 0.10%; 32 mm: 0.45%) but was reduced under the High evaporation rate (0.01%) compared with the Low evaporation rate (0.31%). All rainfall amounts yielded significantly different recoveries of L3 under Low evaporation rates but there was no difference between the 12 and 24 mm treatments under the High evaporation rate. The distribution of simulated rainfall did not significantly affect recovery of infective larvae. Faecal moisture content was positively associated with L3 recovery, as was the ratio of cumulative precipitation and cumulative evaporation (P/E), particularly when measured in the first 4 days post-deposition. The results show that evaporation rate plays a significant role in regulating the influence of rainfall amount on the success of L3 transmission.

Moisture requirements for the free-living development of Haemonchus contortus: quantitative and temporal effects under conditions of low evaporation.

The key influence of moisture availability on development of the free-living stages of Haemonchus contortus is well-documented, although quantitative relationships between moisture variables and development are poorly defined. A factorial experiment (3x2x2) was conducted in programmable incubators to determine the effects of amount and distribution of simulated rainfall on H. contortus development at low evaporation rates (approximately 2 mm/day) under temperatures typical of summers on the Northern Tablelands of NSW, Australia. Sheep faeces containing H. contortus eggs were placed in experimental units containing sterile soil and had one of the three amounts (12, 24 and 32 mm) of simulated rainfall applied, in either a single event on the day after deposition (d 1) or three split events over 6 days (d 1, 3 and 6). Treatments were applied either in week 1 only, or in weeks 1 and 2. Recovery of infective larvae (L3) at 4, 7 and 14 days post-contamination increased with each incremental amount of simulated rainfall over the range of 12-32 mm and was significantly higher under the single "rain" event (2.8%), compared with the three smaller, split events (1.9%). The second application of simulated rainfall in week 2 had only a very small influence on L3 recovery, suggesting that the majority of development to L3 occurred in response to simulated rainfall events in the first 7 days. Both faecal moisture content and the cumulative ratio of precipitation and evaporation (P/E) were strongly and positively correlated with recovery of L3. Recovery of L3 from treatments, which received simulated rainfall in week 1 only was best described by P/E at d 5. Whether the relationships observed in this study hold under field conditions, where macroclimatic conditions such as evaporation rate are substantially more limiting to free-living development, is yet to be determined.

The effects of amount, timing and distribution of simulated rainfall on the development of Haemonchus contortus to the infective larval stage.

Three studies were undertaken to determine the effects of amount, timing and distribution of simulated rainfall on the developmental success of Haemonchus contortus. Faeces containing H. contortus eggs were deposited onto pasture plots under a rainfall-activated retractable roof which eliminated incident rainfall. In October (spring) 2004 and January (summer) 2005, the effects of amount (6, 12, 18 or 24 mm) and timing (1, 4, 8 or 15 days post-faecal deposition) of a single simulated rainfall event was investigated via manual application of water to plots. More H. contortus pre-infective larvae (L1 and L2) developed under the d 1 simulated rainfall treatment than later treatments. There was no effect of rainfall amount on development in either experiment, and negligible development to infective larvae (L3). In February (summer) 2006, the effects of amount (12, 24 or 32 mm) and distribution (single event or three smaller but equal split events over 32 h) of simulated rainfall events was investigated with water applied via sprinkler. In this experiment L3 were recovered from the herbage in one-third of the plots harvested, however recovery was low (0.08% of eggs deposited) and there were no treatment effects. Recovery of L1 and L2 from faeces increased with simulated rainfall amount at d 4, and more L1 and L2 were recovered from the split distribution treatment at d 4. The results indicate that moisture conditions soon after faecal deposition are key determinants of H. contortus development success, with significant penalties on development when simulated rainfall was applied 7 days or more post-deposition, and when the duration of simulated rainfall was short. High rates of evaporation during both summer experiments resulted in rapid drying of the micro-environment and this appears to have limited development to L3.

Ecology of the free-living stages of major trichostrongylid parasites of sheep.

Significant developments over recent decades make it timely to review the ecology of the major gastrointestinal nematode (GIN) species of sheep. These include the relentless development and spread of anthelmintic resistance in all of the major sheep production regions of the world, and the consequent drive towards integrated parasite management (IPM) systems incorporating non-chemotherapeutic strategies such as grazing management. The success of such programs is dependent on a detailed understanding of the environmental influences on the free-living stages of the nematode lifecycle. Major reviews of the subject were conducted prior to 1980, however considerable work has been completed since, including the development of mathematical models describing the epidemiology of GIN infection. Knowledge of the temperature thresholds for free-living development has also improved, while investigations of moisture influences and interactions with temperature have allowed more effective exploitation of environmental effects for IPM. This review re-evaluates our understanding of the factors that determine the success or failure of the free-living phases of the lifecycle in light of these developments. Temperature and moisture are the dominant influences on the free-living stages of Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis, with the effects of pasture conditions playing a significant modulating role. Early in the free-living phase, the developmental success of the three GIN species is limited by susceptibility to cold temperatures. In general, H. contortus is most susceptible, followed by T. colubriformis and then T. circumcincta. The length of the development cycle is dependent largely on temperature, with development rate increasing at warmer temperatures. However, in order for development to proceed to the infective larval stage, addition of moisture is generally required. There has been considerably less work quantifying the effects of moisture on free-living development, although it is clear that H. contortus is most susceptible to desiccation during the pre-infective stages. Once the infective stage is reached, the influences of temperature and moisture on survival are less important, resulting in considerable survival times under conditions lethal to pre-infective stages. However, hot, dry conditions can be lethal for infective larvae of all three species, while extreme cold is also lethal with significant species variation. While the existing body of knowledge is substantial, the interpretation of many studies and comparison between them is complicated by inadequate description of, or variation in, the environmental measurements used. Confounding the effects of environmental variables on development to infective stage is the migration of larvae from the faeces and subsequent survival on pasture. There is a need to build on recent efforts to explore interaction between the effects of temperature and moisture, and also the trend to more closely simulate field conditions in laboratory studies. We propose a logical framework for future ecological investigations to overcome some of these problems, facilitate the development of a more integrated dataset on the subject and improve prediction of free-living development.

Which is the best phenotypic trait for use in a targeted selective treatment strategy for growing lambs in temperate climates?

Targeted selective treatment (TST) requires the ability to identify the animals for which anthelmintic treatment will result in the greatest benefit to the entire flock. Various phenotypic traits have previously been suggested as determinant criteria for TST; however, the weight gain benefit and impact on anthelmintic efficacy for each determinant criterion is expected to be dependent upon the level of nematode challenge and the timing of anthelmintic treatment. A mathematical model was used to simulate a population of 10,000 parasitologically naïve Scottish Blackface lambs (with heritable variation in host-parasite interactions) grazing on medium-quality pasture (grazing density=30 lambs/ha, crude protein=140g/kg DM, metabolisable energy=10MJ/kg DM) with an initial larval contamination of 1000, 3000 or 5000 Teladorsagia circumcincta L3/kg DM. Anthelmintic drenches were administered to 0, 50 or 100% of the population on a single occasion. The day of anthelmintic treatment was independently modelled for every day within the 121day simulation. Where TST scenarios were simulated (50% treated), lambs were either chosen by random selection or according to highest faecal egg count (FEC, eggs/g DM faeces), lowest live weight (LW, kg) or lowest growth rate (kg/day). Average lamb empty body weight (kg) and the resistance (R) allele frequency amongst the parasite population on pasture were recorded at slaughter (day 121) for each scenario. Average weight gain benefit and increase in R allele frequency for each determinant criterion, level of initial larval contamination and day of anthelmintic treatment were calculated by comparison to a non-treated population. Determinant criteria were evaluated according to average weight gain benefit divided by increase in R allele frequency to determine the benefit per R. Whilst positive phenotypic correlations were predicted between worm burden and FEC; using LW as the determinant criterion provided the greatest benefit per R for all levels of initial larval contamination and day of anthelmintic treatment. Hence, LW was identified as the best determinant criterion for use in a TST regime. This study supports the use of TST strategies as benefit per R predictions for all determinant criteria were greater than those predicted for the 100% treatment group, representing an increased long-term productive benefit resulting from the maintenance of anthelmintic efficacy. Whilst not included in this study, the model could be extended to consider other parasite species and host breed parameters, variation in climatic influences on larval availability and grass growth, repeated anthelmintic treatments and variable proportional flock treatments.

The specific diagnosis of gastrointestinal nematode infections in livestock: larval culture technique, its limitations and alternative DNA-based approaches.

The specific diagnosis of gastrointestinal nematode infections in ruminants is routinely based on larval culture technique and on the morphological identification of developed third-stage larvae. However, research on the ecology and developmental requirements of different species suggests that environmental conditions (e.g., temperature and humidity) for optimal development to occur vary between the different species. Thus, employing a common culture protocol for all species will favour the development of certain species over others and can cause a biased result in particular when species proportions in a mixed infection are to be determined. Furthermore, the morphological identification of L3 larvae is complicated by a lack of distinctive, obvious features that would allow the identification of all key species. In the present paper we review in detail the potential limitations of larval culture technique and morphological identification and provide account to some modern molecular alternatives to the specific diagnosis of gastrointestinal nematode infection in ruminants.

Measurement of phenotypic resilience to gastro-intestinal nematodes in Merino sheep and association with resistance and production variables.

A cross-over experiment was conducted to compare six different phenotypic measures of resilience to gastro-intestinal nematodes (predominantly Haemonchus contortus) in Merino sheep and their association with resistance and production levels. On each of six farms, 120 ewes born in 2006 and 120 older mixed age ewes were selected at shearing in 2007. Of these, 60 in each mob were serially treated with long-acting anthelmintics to suppress worm populations. The other 60 ewes were managed according to management practices employed on the farm (infected, INF). At shearing in 2008, the experimental sheep had their anthelmintic treatments switched. The experiment concluded at shearing in 2009. Measures of resilience were greasy fleece weight (GFW), live weight gain (LWG) and haematocrit (HCT) when infected and the difference in these variables between infected and suppressed. Resistance was determined from multiple faecal worm egg counts (WEC) when infected. Measures of resilience based on GFW, LWG and HCT were moderately correlated with each other (r=0.25-0.50) suggesting that they represent different traits. Correlations between a measure in infected animals, and the difference in the same measurement between infected and uninfected animals were higher (r=-0.37 to -0.82), indicating that measurement during infection is an adequate measure of resilience. WEC was negatively correlated with LWG and HCT during infection but not GFW. Correlations with resilience measures based on difference between infected and uninfected were positive. Surviving infected sheep were found to have higher haematocrit (HCT), and lower WEC in summer and autumn than sheep that died following the measurement. These results show that measurement of performance traits while infected is a reasonable approximation of measurement of resilience based on the difference in performance between infected and non-infected. They also show that resilience to worm infection is not a single trait, but rather a suite of moderately correlated traits.