Prospects of breeding small ruminants for resistance to internal parasites

The current status and outlook for insecticide, acaricide and anthelmintic resistances across the Australian ruminant livestock industries: assessing the threat these resistances pose to the livestock sector

The Australian ruminant livestock industries are faced with the need to control parasitic infectious diseases that can seriously impact the health of animals. However, increasing levels of resistance to insecticides, anthelmintics and acaricides are substantially reducing the ability to control some of these parasites. Here we review the current situation with regard to chemical resistances in parasites across the various sectors of the Australian ruminant livestock industries and assess the level of threat that these resistances pose to the sustainability of these sectors in the short to long terms. We also look at the extent to which testing for resistance occurs across the various industry sectors, and hence how well-informed these sectors are of the extent of chemical resistance. We examine on-farm management practices, breeding of parasite-resistant animals, and non-chemical therapeutics that may act as short to long term means to reduce the current reliance on chemicals for parasite control. Finally, we look at the balance between the prevalence and magnitude of current resistances and the availability and adoption rates of management, breeding and therapeutic alternatives in order to assess the parasite control outlook for the various industry sectors.

Secretory IgA as Biomarker for Gastrointestinal Nematodes Natural Infection in Different Breed Sheep

Specific IgA antibody has been shown to play an important role in resistance to gastrointestinal nematode (GIN) infections in sheep, particularly in Teladorsagia circumcincta parasitosis. In some breeds, negative associations have been shown between IgA levels and worm burden in experimentally infected sheep. In the present study, we have studied the relationship between IgA levels in naturally infected sheep (582 ewes in total; 193 younger than one year old and 389 older than one year old) and fecal egg count (FEC) in the Assaf, Castellana, and Churra breeds. ELISA assays were performed to measure IgA levels against the somatic antigen of T. circumcincta third larval stage (L₃) and a 203-amino-acid fragment of the protein disulfide isomerase from the same GIN species. A multilevel random intercept model was developed to predict the infection risk according to age or breed. Spearman's correlation rank was used for statistical analysis. The prediction model showed that breed was not an influential factor in this study, although the Assaf breed could be considered slightly more susceptible than the others. In addition, age affected the infection risk, with the young ewes more susceptible to infection than the adult groups, except for the Castellana breed, whose risk of infection was similar at all ages. The most significant positive association was found between FEC and IgA measured in the nasal secretions of young ewes using both antigens (Rho = 0.5; p = 0.00); the correlation of FEC with IgA in serum was moderately significant (Rho = 0.306; p = 0.00). Comparing both antigens, the protein disulfide isomerase antigen was less reactive than the somatic antigen from L₃. In conclusion, under natural conditions, specific IgA against GIN was positively associated with FEC in sheep, with nasal secretions from young animals being the sample where this association is stronger, which, therefore, could be used as a marker of infection in further studies.

Carbohydrate larval antigen (CarLA IgA) responses to mixed species nematode infection in pasture grazed Angora goats

The genetics of indicator traits for resistance of Angora goats to gastrointestinal nematode parasite infections, and their relationships with productivity traits, were investigated on a commercial mixed-enterprise farm in the eastern North Island of New Zealand. Faecal egg counts (FEC), specific Immunoglobulin A (IgA) and Immunoglobulin G (IgG) antibody titres against carbohydrate larval antigen (CarLA) in saliva, live weight and fleece weights were recorded from 278 goats of 19-20 months of age, run as four separate mobs (breeding bucks, castrated males (wethers), or 2 groups of breeding does). Summary statistics showed the mobs differed significantly in liveweight, log_e (FEC+50), log_e (IgA) and log_e (IgG). Genetic parameters were estimated using an animal model with repeated records where appropriate, after adjusting for the different contemporary animal groups, using the restricted maximum likelihood (REML) package. Heritability estimates from repeated measures were 0.19 ± 0.16 for FEC, 0.28 ± 0.16 for CarLA specific IgA and 0.23 ± 0.15 for CarLA specific IgG. The CarLA specific IgA response was negatively genetically correlated with FEC (-0.99 ± 0.31) suggesting that it could be used as a selection tool for breeding resistant animals. Although the genetic and phenotypic correlations between CarLA IgA and IgG were high and significant, the analysis between log_e (FEC+50) and log_e CarLA IgG did not converge. Further, both FEC and CarLA IgA showed significant and favourable genetic correlations with live weight. In contrast, CarLA IgG showed an unfavourable phenotypic correlation with liveweight. While this is only a preliminary study, the results do suggest that the immunoassay measuring salivary CarLA IgA response may have utility as a selection tool for parasite resistance in some breeds of goats.

Classification Performance of Machine Learning Methods for Identifying Resistance, Resilience, and Susceptibility to Haemonchus contortus Infections in Sheep

This study investigated the feasibility of using easy-to-measure phenotypic traits to predict sheep resistant, resilient, and susceptible to gastrointestinal nematodes, compared the classification performance of multinomial logistic regression (MLR), linear discriminant analysis (LDA), random forest (RF), and artificial neural network (ANN) methods, and evaluated the applicability of the best classification model on each farm. The database comprised 3654 records of 1250 Santa Inês sheep from 6 farms. The animals were classified into resistant (2605 records), resilient (939 records), and susceptible (110 records) according to fecal egg count and packed cell volume. A random oversampling method was performed to balance the dataset. The classification methods were fitted using the information of age class, the month of record, farm, sex, Famacha© degree, body weight, and body condition score as predictors, and the resistance, resilience, and susceptibility to gastrointestinal nematodes as the target classes to be predicted considering data from all farms randomly. An additional leave-one-farm-out cross-validation technique was used to assess prediction quality across farms. The MLR and LDA models presented good performances in predicting susceptible and resistant animals. The results suggest that the use of readily available records and easily measurable traits may provide useful information for supporting management decisions at the farm level.

Status of gastrointestinal nematode infections and associated epidemiological factors in sheep from Córdoba, Colombia

Gastrointestinal nematodes cause serious economic losses in sheep production systems. To determine the prevalence and risk factors associated with these parasites, a study was conducted on 595 sheep in Córdoba, Colombia. Prevalence and parasite burden were determined using the McMaster technique. Larvae were cultured from feces to identify the nematode genera. For the analysis of associated factors and parasite burden, data means, medians, and confidence intervals were compared. A georeferenced data analysis was performed and an epidemiological map was constructed. An overall prevalence of 88.2% was found, with the highest prevalence and parasite burden for Strongylida (83.2%) and Strongyloides (41%) nematodes. The mean parasite burden was 1255 eggs per gram. The gastrointestinal nematode genera identified were Trichostrongylus, Strongyloides, Haemonchus, Oesophagostomum, Bunostomum, and Cooperia. In general, a significant association was found between parasite burden and dewormed animals, anthelmintic used, date of last deworming, and breeds. The FAMACHA® method and body condition showed a significant association with the Strongylida parasite burden. Clusters with higher intensity of gastrointestinal nematode burden and high prevalence were observed in the regions of Bajo Sinú, Sinú Medio, and San Jorge.

A Review of the Impact of Climate Change on the Epidemiology of Gastrointestinal Nematode Infections in Small Ruminants and Wildlife in Tropical Conditions

Climate change is causing detrimental changes in living organisms, including pathogens. This review aimed to determine how climate change has impacted livestock system management, and consequently, what factors influenced the gastrointestinal nematodes epidemiology in small ruminants under tropical conditions. The latter is orientated to find out the possible solutions responding to climate change adverse effects. Climate factors that affect the patterns of transmission of gastrointestinal parasites of domesticated ruminants are reviewed. Climate change has modified the behavior of several animal species, including parasites. For this reason, new control methods are required for controlling parasitic infections in livestock animals. After a pertinent literature analysis, conclusions and perspectives of control are given.

Cluster analysis to explore additive-genetic patterns for the identification of sheep resistant, resilient and susceptible to gastrointestinal nematodes

Infection caused by gastrointestinal nematodes is an important issue for animal health and production. Controlling worm infections improves the sustainability of the sheep industry. Genetic selection of animals that are resistant to gastrointestinal nematodes is another strategy to render sheep production more sustainable by decreasing the use of anthelmintics. The aims of this study were (1) to explore the additive-genetic pattern of EBVs for Famacha© (FAM), packed-cell volume (PVC), and fecal egg counts (FEC) of Santa Ines sheep, (2) to propose a classification of animals that are resistant, resilient and susceptible to gastrointestinal nematodes based on their additive-genetic patterns, and (3) to identify the most suitable animals for selection based on their genetic pattern. A dataset of 2,241 records from 747 animals was used to predict the breeding values for indicator traits of resistance to gastrointestinal nematodes with THRGIBBS1F90 and to carry out cluster analyses was used R software. Three clusters of animals were found in the population using hierarchical cluster analysis of the breeding values for FAM, PCV and FEC. Each cluster was characterized by different additive-genetic patterns identified by k-means non-hierarchical cluster analysis. Among a total of 747 animals, 196 were classified as resistant, 288 as resilient, and 263 as susceptible. Cluster analysis is a valuable tool for data screening that permits to evaluate only selection candidates based on their additive-genetic pattern for gastrointestinal nematode resistance. EBVs for FEC were decisive to divide the population into resilient, resistant and susceptible animals. It is also important to include the EBVs for PCV and FAM to adequately distinguish resistant from resilient animals. Finally, the resistant cluster consisted of the most desirable animals to be used as selection candidates in order to genetically improve resistance to infection with gastrointestinal nematodes. This cluster contained animals with the most appropriate additive-genetic pattern to achieve the breeding goal, with positive breeding values for PCV and negative breeding values for FAM and FEC.

Point of care colourimetric and lateral flow LAMP assay for the detection of Haemonchus contortus in ruminant faecal samples

In this study, we present an optimised colourimetric and a lateral flow LAMP assay for the detection of Haemonchus contortus in small ruminant faecal samples. Using a previously published LAMP primer set, we made use of commercially available colourimetric LAMP and lateral flow kits and combined this into an optimised diagnostic assay which was then tested on field faecal samples from Eastern and South-Eastern Hungary as well as a pure H. contortus egg faecal sample from Košice, Slovakia. Both assays showed no conflicts in visual detection of the results. Additionally, we modified and tested several centrifuge-free DNA extraction methods and one bead-beating egg lysis DNA extraction method to develop a true point of care protocol, as the source of the starting DNA is the main rate-limiting step in farm-level molecular diagnosis. Out of the various methods trialed, promising results were obtained with the magnetic bead extraction method. Sample solutions from the Fill-FLOTAC^® technique were also utilised, which demonstrated that it could be efficiently adapted for field-level egg concentration to extract DNA. This proof of concept study showed that isothermal amplification technologies with a colourimetric detection or when combined with a lateral flow assay could be an important step for a true point of care molecular diagnostic assay for H. contortus.

A journey through 50 years of research relevant to the control of gastrointestinal nematodes in ruminant livestock and thoughts on future directions

This review article provides an historical perspective on some of the major research advances of relevance to ruminant livestock gastrointestinal nematode control over the last 50 years. Over this period, gastrointestinal nematode control has been dominated by the use of broad-spectrum anthelmintic drugs. Whilst this has provided unprecedented levels of successful control for many years, this approach has been gradually breaking down for more than two decades and is increasingly unsustainable which is due, at least in part, to the emergence of anthelmintic drug resistance and a number of other factors discussed in this article. We first cover the remarkable success story of the discovery and development of broad-spectrum anthelmintic drugs, the changing face of anthelmintic drug discovery research and the emergence of anthelmintic resistance. This is followed by a review of some of the major advances in the increasingly important area of non-pharmaceutical gastrointestinal nematode control including immunology and vaccine development, epidemiological modelling and some of the alternative control strategies such as breeding for host resistance, refugia-based methods and biological control. The last 50 years have witnessed remarkable innovation and success in research aiming to improve ruminant livestock gastrointestinal nematode control, particularly given the relatively small size of the research community and limited funding. In spite of this, the growing global demand for livestock products, together with the need to maximise production efficiencies, reduce environmental impacts and safeguard animal welfare - as well as specific challenges such as anthelmintic drug resistance and climate change- mean that gastrointestinal nematode researchers will need to be as innovative in the next 50 years as in the last.

Haemonchosis: A Challenging Parasitic Infection of Sheep and Goats

The paper reviews the challenges about haemonchosis-a significant and common parasitic infection of small ruminants. Haemonchus contortus is a highly pathogenic parasite that localises in the abomasum of affected animals and exerts its pathogenicity by blood-sucking activity, adversely affecting the health and productivity of animals. The first challenge is the uneven distribution of the infection globally, this being more prevalent in tropical and subtropical and warm temperate and summer rainfall regions than in cool and cold temperate and arid regions; hence, this leads in differences in the approaches required for its control. Another challenge is the widespread presence of Haemonchus strains resistant to the various anthelmintics available: Benzimidazoles, imidazothiazoles, macrocyclic lactones, closantel and monepantel, which makes the control of the infection difficult. The third challenge refers to the difficulty of diagnosing the disease, given that field evidence can provide suspicion about the infection, which needs to be subsequently confirmed by laboratory tests through parasitological or molecular techniques. The final challenge relates to the difficulties in the control of the infection and the necessity to use pharmaceutical products cautiously and with a planned approach, to avoid further development of anthelmintic resistance, also given that use of a recently licenced vaccine is not widespread. In conclusion, at the moment, we should be concerned, but not worried, about this infection, and apply correctly the appropriate health management plans.

Advances in the discovery and development of anthelmintics by harnessing natural product scaffolds

Widespread resistance to currently-used anthelmintics represents a major obstacle to controlling parasitic nematodes of livestock animals. Given the reliance on anthelmintics in many control regimens, there is a need for the continued discovery and development of new nematocides. Enabling such a focus are: (i) the major chemical diversity of natural products; (ii) the availability of curated, drug-like extract-, fraction- and/or compound-libraries from natural sources; (iii) the utility and practicality of well-established whole-worm bioassays for Haemonchus contortus-an important parasitic nematodes of livestock-to screen natural product libraries; and (iv) the availability of advanced chromatographic (HPLC), spectroscopic (NMR) and spectrometric (MS) techniques for bioassay-guided fractionation and structural elucidation. This context provides a sound basis for the identification and characterisation of anthelmintic candidates from natural sources. This chapter provides a background on the importance and impact of helminth infections/diseases, parasite control and aspects of drug discovery, and reviews recent work focused on (i) screening well-defined compound libraries to establish the methods needed for large-scale screening of natural extract libraries; (ii) discovering plant and marine extracts with nematocidal or nematostatic activity, and purifying bioactive compounds and assessing their potential for further development; and (iii) synthesising analogues of selected purified natural compounds for the identification of possible 'lead' candidates. The chapter describes some lessons learned from this work and proposes future areas of focus for drug discovery. Collectively, the findings from this recent work show potential for selected natural product scaffolds as candidates for future development. Developing such candidates via future chemical optimisation, efficacy and safety evaluations, broad spectrum activity assessments, and target identification represents an exciting prospect and, if successful, could pave the way to subsequent pre-clinical and clinical evaluations.

Influence of environmental factors on the detection of blood in sheep faeces using visible-near-infrared spectroscopy as a measure of Haemonchus contortus infection

BACKGROUND

Existing diagnostic methods for the parasitic gastrointestinal nematode, Haemonchus contortus, are time consuming and require specialised expertise, limiting their utility in the field. A practical, on-farm diagnostic tool could facilitate timely treatment decisions, thereby preventing losses in production and flock welfare. We previously demonstrated the ability of visible-near-infrared (Vis-NIR) spectroscopy to detect and quantify blood in sheep faeces with high accuracy. Here we report our investigation of whether variation in sheep type and environment affect the prediction accuracy of Vis-NIR spectroscopy in quantifying blood in faeces.

METHODS

Visible-NIR spectra were obtained from worm-free sheep faeces collected from different environments and sheep types in South Australia (SA) and New South Wales, Australia and spiked with various sheep blood concentrations. Spectra were analysed using principal component analysis (PCA), and calibration models were built around the haemoglobin (Hb) wavelength region (387-609 nm) using partial least squares regression. Models were used to predict Hb concentrations in spiked faeces from SA and naturally infected sheep faeces from Queensland (QLD). Samples from QLD were quantified using Hemastix® test strip and FAMACHA© diagnostic test scores.

RESULTS

Principal component analysis showed that location, class of sheep and pooled versus individual samples were factors affecting the Hb predictions. The models successfully differentiated 'healthy' SA samples from those requiring anthelmintic treatment with moderate to good prediction accuracy (sensitivity 57-94%, specificity 44-79%). The models were not predictive for blood in the naturally infected QLD samples, which may be due in part to variability of faecal background and blood chemistry between samples, or the difference in validation methods used for blood quantification. PCA of the QLD samples, however, identified a difference between samples containing high and low quantities of blood.

CONCLUSION

This study demonstrates the potential of Vis-NIR spectroscopy for estimating blood concentration in faeces from various types of sheep and environmental backgrounds. However, the calibration models developed here did not capture sufficient environmental variation to accurately predict Hb in faeces collected from environments different to those used in the calibration model. Consequently, it will be necessary to establish models that incorporate samples that are more representative of areas where H. contortus is endemic.

Sustainable Approaches to Parasite Control in Ruminant Livestock

It is increasingly difficult to manage and control gastrointestinal nematode parasites in pasture-based ruminant livestock operations because of the high prevalence of anthelmintic resistance. Anthelmintics should be combined with alternative forms of control. Sustainable tools include copper oxide wire particles and condensed tannin-rich plants, which target primarily Haemonchus contortus in small ruminants. Nematophagous fungi reduce larvae on pasture and target nematode larvae in feces of most livestock species. In addition, and perhaps most importantly, genetic selection focuses on parasite resistance. Producers should use as many tools as possible to minimize the need for pharmaceutical interventions and optimize animal production.

Genome-wide association study to identify genetic loci associated with gastrointestinal nematode resistance in Katahdin sheep

Resistance to gastrointestinal nematodes has previously been shown to be a moderately heritable trait in some breeds of sheep, but the mechanisms of resistance are not well understood. Selection for resistance currently relies upon faecal egg counts (FEC), blood packed cell volumes and FAMACHA visual indicator scores of anaemia. Identifying genomic markers associated with disease resistance would potentially improve the selection process and provide a more reliable means of classifying and understanding the biology behind resistant and susceptible sheep. A GWAS was conducted to identify possible genetic loci associated with resistance to Haemonchus contortus in Katahdin sheep. Forty animals were selected from the top and bottom 10% of estimated breeding values for FEC from a total pool of 641 sires and ram lambs. Samples were genotyped using Applied Biosystems™ Axiom™ Ovine Genotyping Array (50K) consisting of 51 572 SNPs. Following quality control, 46 268 SNPs were included in subsequent analyses. Analyses were conducted using a linear regression model in plink v1.90 and a single‐locus mixed model in snp and variation suite. Genome‐wide significance was determined by a Bonferroni correction for multiple testing. Using linear regression, loci on chromosomes 2, 3, 16, 23 and 24 were significantly associated at the genome level with FEC estimated breeding values, and we identified a region on chromosome 2 that was significant using both statistical analyses. We suggest a potential role for the gene DIS3L2 for gastrointestinal nematode resistance in Katahdin sheep, although further research is needed to validate these findings.

Morada Nova sheep breed: Resistant or resilient to Haemonchus contortus infection?

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Resistance against Haemonchus contortus was assessed in a Morada Nova flock.

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More than 88% of the lambs had PCV ≥ 24% even with high fecal egg counts (FEC).

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Only susceptible lambs had decreased live weight due to parasitism.

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More than 98% of the ewes had FEC below 4000 EPG.

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PCV of the ewes was not affected by H. contortus infection.

Morada Nova is a Brazilian hair sheep breed that is well adapted to the country’s mainly tropical climate and has good potential for meat and leather production. This breed is reported to be resistant to Haemonchus contortus infection, a highly desired characteristic due to the large impact of this parasite on sheep farming. Therefore, the present study aimed to characterize 287 recently weaned Morada Nova lambs and 123 ewes in relation to their resistance against H. contortus. The animals were dewormed and 15 days later artificially infected with 4000 H. contortus L₃ (D0). They were individually monitored by periodic assessment of fecal egg count (FEC), packed cell volume (PCV), and live weight (LW). On D42, the sheep were again dewormed and submitted to a new parasitic challenge, following the same scheme. The animals of each category (lambs and ewes) were ranked according to individual mean FEC values, and classified as resistant (R, 20%), intermediate (I, 60%), or susceptible (S, 20%) to H. contortus infection. At weaning, high FEC were observed in all three phenotypes (P > 0.05). After the artificial infections, there was a significant difference (P < 0.05) among the three lamb phenotypes for the mean FEC (R < I < S), PCV (R > I > S), and LW (R = I > S). The infection levels (FEC) were negatively correlated with PCV (r = -0.66; P < 0.001), and LW (r = -0.30; P < 0.001). Despite this, the lambs were resilient, since more than 88% of these animals maintained the PCV above 24%, even when heavily infected. The importance of selective parasite control before weaning to reduce the negative impact on slaughter weight was evidenced, taking into account the high positive correlation between LW at weaning and final LW (r = 0.73; P < 0.001). The ewes, in turn, were strongly resistant to the parasite. Despite highly significant differences (P < 0.001) for mean FEC between phenotypes (R < I < S), 98% of the ewes maintained FEC below 4000 EPG. Their health was not affected, since PCV and LW did not differ between phenotypes, and these parameters were not significantly correlated with FEC (P > 0.05). With the phenotypic characterization performed here, it is possible to introduce procedures for parasite control in Morada Nova flocks, facilitating the target-selective treatment approach. The results of this study can also support improvement of meat production by the Morada Nova breed.

Genetic parameters for faecal worm egg count at different ages in Australian sheep under natural challenge

The data used in the present study consisted of 24535 worm egg count records on sheep observed from 63 to 560 days of age under conditions of the natural challenge of trichostrongylid species. Records were extracted from the Information Nucleus Flock database of the Australia Sheep Cooperative Research Centre program from 2007 to 2011. Records were observed at various ages and subdivided into weaning (W, ~3 months), post-weaning (P, ~4 months), yearling (Y, ~12 months) and hogget (H, ~18 months) age stages and were used to investigate genetic variation at different age stages in univariate analyses and estimate genetic correlations between age stages in multi-trait analyses. The full data were also analysed by random regression models to study how heritability and genetic correlations varied with age. Heritability estimates from univariate analyses were 0.20 ± 0.05, 0.15 ± 0.02, 0.36 ± 0.09, 0.22 ± 0.06 for W, P, Y and H age stages respectively. A similar trend of heritability over ages was found from random regression analyses, which decreased from 0.16 at 90 days to 0.09 at 120 days, following a steady increase to 0.32 at ~410 days, and then decreased afterwards to 0.24 at 520 days. Strong genetic correlations (&gt;0.8) were found between W and P age stages, along with Y and H age stages. Sire by flock interaction effects were significant, and accounted for the reduced estimates of heritability and increased genetic correlations between age stages. The results indicated that a multiple-trait approach is required for genetic evaluation of worm egg count when measurements are at different ages, and the accuracy of evaluations would benefit from recording at least two separate age stages.

Derivation of the economic value of R0 for macroparasitic diseases and application to sea lice in salmon

BACKGROUND

Macroparasites, such as ticks, lice, and helminths, are a concern in livestock and aquaculture production, and can be controlled by genetic improvement of the host population. Genetic improvement should aim at reducing the rate at which parasites spread across the farmed population. This rate is determined by the basic reproduction ratio, i.e. [Formula: see text], which is the appropriate breeding goal trait. This study aims at providing a method to derive the economic value of [Formula: see text].

METHODS

Costs of a disease are the sum of production losses and expenditures on disease control. Genetic improvement of [Formula: see text] lowers the loss-expenditure frontier. Its economic effect depends on whether the management strategy is optimized or not. The economic value may be derived either from the reduction in losses with constant expenditures or from the reduction in expenditures with constant losses.

RESULTS

When [Formula: see text] ≤ 1, the economic value of a further reduction is zero because there is no risk of a major epidemic. When [Formula: see text] > 1 and management is optimized, the economic value increases with decreasing values of [Formula: see text], because both the mean number of parasites per host and frequency of treatments decrease at an increasing rate when [Formula: see text] decreases. When [Formula: see text] > 1 and management is not optimized, the economic value depends on whether genetic improvement is used for reducing expenditures or losses. For sea lice in salmon, the economic value depends on a reduction in expenditures with constant losses, and is estimated to be 0.065€/unit [Formula: see text]/kg production.

DISCUSSION

Response to selection for measures of disease prevalence cannot be predicted from quantitative genetic theory alone. Moreover, many studies fail to address the issue of whether genetic improvement results in reduced losses or expenditures. Using [Formula: see text] as the breeding goal trait, weighed by its appropriate economic value, avoids these issues.

CONCLUSION

When management is optimized, the economic value increases with decreasing values of [Formula: see text] (until the threshold of [Formula: see text], where it drops to zero). When management is not optimized, the economic value depends on whether genetic improvement is used for reduced expenditures or production losses. For sea lice in salmon, the economic value is estimated to be 0.065 €/unit [Formula: see text]/kg production.

Control of helminth ruminant infections by 2030

Helminth infections have large negative impacts on production efficiency in ruminant farming systems worldwide, and their effective management is essential if livestock production is to increase to meet future human needs for dietary protein. The control of helminths relies heavily on routine use of chemotherapeutics, but this approach is unsustainable as resistance to anthelmintic drugs is widespread and increasing. At the same time, infection patterns are being altered by changes in climate, land-use and farming practices. Future farms will need to adopt more efficient, robust and sustainable control methods, integrating ongoing scientific advances. Here, we present a vision of helminth control in farmed ruminants by 2030, bringing to bear progress in: (1) diagnostic tools, (2) innovative control approaches based on vaccines and selective breeding, (3) anthelmintics, by sustainable use of existing products and potentially new compounds, and (4) rational integration of future control practices. In this review, we identify the technical advances that we believe will place new tools in the hands of animal health decision makers in 2030, to enhance their options for control and allow them to achieve a more integrated and sustainable approach to helminth control in support of animal welfare and production.

Immunogenomics of gastrointestinal nematode infection in ruminants - breeding for resistance to produce food sustainably and safely

Gastrointestinal nematode (GIN) infection of ruminants represents a major health and welfare challenge for livestock producers worldwide. The emergence of anthelmintic resistance in important GIN species and the associated animal welfare concerns have stimulated interest in the development of alternative and more sustainable strategies aimed at the effective management of the impact of GINs. These integrative strategies include selective breeding using genetic/genomic tools, grazing management, biological control, nutritional supplementation, vaccination and targeted selective treatment. In this review, the logic of selecting for "resistance" to GIN infection as opposed to "resilience" or "tolerance" is discussed. This is followed by a review of the potential application of immunogenomics to genetic selection for animals that have the capacity to withstand the impact of GIN infection. Advances in relevant genomic technologies are highlighted together with how these tools can be advanced to support the integration of immunogenomic information into ruminant breeding programmes.

The genetic basis for the selection of dairy goats with enhanced resistance to gastrointestinal nematodes

Gastrointestinal nematodes (GIN) severely affect small ruminant production worldwide. Increasing problems of anthelmintic resistance have given strong impetus to the search for alternative strategies to control GIN. Selection of animals with an enhanced resistance to GIN has been shown to be successful in sheep. In goats, the corresponding information is comparatively poor. Therefore, the present study was designed to provide reliable data on heritabilities of and genetic correlations between phenotypic traits linked to GIN and milk yield in two major dairy goat breeds (Alpine and Saanen). In all, 20 herds totalling 1303 goats were enrolled in the study. All herds had (i) a history of gastrointestinal nematode infection, (ii) uniform GIN exposure on pasture and (iii) regular milk recordings. For all goats, individual recordings of faecal egg counts (FEC), FAMACHA© eye score, packed cell volume (PCV) and milk yield were performed twice a year with an anthelmintic treatment in between. The collected phenotypic data were multivariately modelled using animal as a random effect with its covariance structure inferred from the pedigree, enabling estimation of the heritabilities of the respective traits and the genetic correlation between them. The heritabilities of FEC, FAMACHA© and PCV were 0.07, 0.22 and 0.22, respectively. The genetic correlation between FEC and FAMACHA© was close to zero and -0.41 between FEC and PCV. The phenotypic correlation between FEC and milk yield was close to zero, whereas the genetic correlation was 0.49. Our data suggest low heritability of FEC in Saanen and Alpine goats and an unfavourable genetic correlation of FEC with milk yield.

Can the amount of digestible undegraded protein offered to ewes in late pregnancy affect the periparturient change in resistance to gastrointestinal nematodes?

Ewes experience a temporary decline in resistance to gastrointestinal nematodes (GIN) during the periparturient period, characterised by a rise in faecal egg count (FEC) that represents a major source of pasture contamination for naïve progeny. The aim of this study was to assess the effect of level of supplementation with digestible undegraded protein (DUP) during the last 6 weeks of pregnancy on periparturient FEC and the performance of ewes with a naturally acquired parasite infection. Eighty-five Belclare and Belclare x Scottish Blackface twin/triplet-bearing ewes were allocated to 1 of 4 dietary groups representing the combination of 2 concentrates (DUP concentration 29 and 94g/kg dry matter) with 2 levels of concentrate during the final 6 weeks of gestation (18 and 30kg in total for ewes with twins; 24 and 35kg for ewes with triplets). All ewes were housed during the pre-partum feeding period and offered grass silage ad libitum; food intake was recorded daily. The intake of DUP varied from 26 to 72g/d among treatments and was reflected in variation of 0.76 to 1.20 in metabolizable protein supply as a proportion of requirements. After lambing, ewes and lambs grazed on permanent sheep pasture, without concentrate supplementation, until weaning (14 weeks post lambing). The variables studied, from week 6 pre-lambing up to week 10 post-lambing, included: FEC, serum pepsinogen concentration, body weight (BW) and body condition score (BCS). The effect of week (relative to lambing date) on FEC was highly significant (P<0.001). However, diet did not influence FEC (P>0.05) at any stage either pre- or post-partum. Pepsinogen concentration also varied with time but was not influenced by dietary treatment (P>0.05). The changes in BW and BCS from 6 weeks before lambing to weaning were not affected by the concentration of DUP in the supplement but ewes on treatments involving the higher level of supplementation lost less BW and BCS (P<0.001). The results of this study indicate that the level of DUP supplementation during the last 6 weeks of pregnancy does not affect FEC, BW or BCS of housed ewes with a naturally acquired GIN infection.

Immunomodulatory effects of adult Haemonchus contortus excretory/secretory products on human monocyte-derived dendritic cells

The levels of expression of surface molecules and release of cytokines and chemokines of human monocyte-derived dendritic cells were determined after their exposure to adult H. contortus excretory/secretory (ES) products or a combination of ES products and bacterial lipopolysaccharide (LPS). Worm products provoked a weak response and only partial maturation of the dendritic cells, consistent with the hyporesponsiveness and more tolerogenic immune environment present in parasitized animals and humans. Co-stimulation with LPS demonstrated that H. contortus secretions, like those of other helminths, contain immunomodulators capable of reducing some aspects of the strong T(H)1/T(H)2 response evoked by bacterial LPS. There were significant reductions in the release of some cytokine/chemokines by LPS-stimulated mdDCs and a trend (although not significant at P < 0.05) for reduced expression levels of CD40, CD80 and HLA-DR. A prominent feature was the variability in responses of dendritic cells from the four donors, even on different days in repeat experiments, suggesting that generalized conclusions may be difficult to make, except in genetically related animals. Such observations may therefore be applicable only to restricted populations. In addition, previous exposure to parasites in a target population for immunomodulatory therapy may be an important factor in assessing the likelihood of adverse reactions or failures in the treatment to worm therapy.

Selection of sheep for response to Trichostrongylus colubriformis larvae: genetic parameters

Data were analysed from a long-term selection experiment with Merino sheep, based on immunological responsiveness to the intestinal nematode Trichostrongylus colubriformis. For the first 14 years of selection, the criterion was the mean of five fortnightly faecal worm-egg counts (FECs) of pen-housed lambs that were vaccinated with irradiated larvae then challenged with normal T. colubriformis larvae. For most of the lambs born in the subsequent 6 years, the selection criterion was the mean of three weekly FECs of grazing lambs following a secondary challenge with T. colubriformis larvae. Data from 2233 lambs were included in the analyses.

At the end of the experiment, the lines selected for high and low response to challenge differed by 2·3 to 2·9 phenotypic standard deviations. The heritability of average pen-tested FEC was 0·38 (s.e. 0·04), similar to that for average FEC after secondary field challenge (0·37, s.e. 007). Average FECs from the primary field challenge were less heritable (0·21, s.e. 006). Counts recorded on pen-tested animals at 3, 5, 7, 9 and 11 weeks after infection were all highly correlated genetically (estimates 0·93 to 0·99) and of similar heritability (0·33 to 0·39) with a non-significant tendency for later FECs to be more heritable. Phenotypic correlations were lower, ranging from 0·60 for counts 8 weeks apart, to 0·78 to 0·81 for adjacent samples 2 weeks apart. Single-record heritability estimates at 3, 4 and 5 weeks after secondary infection in grazing lambs did not differ statistically from each other but were highest at the 5th week after infection at 0·33 (s.e. 007).

FECs determined in pens were imperfectly correlated with FECs determined at pasture (genetic correlation 0·72, s.e. 013). Phenotypic correlations of single-record FECs across primary and secondary field challenges were low (around 0·2), although the genetic correlation between mean primary FEC and mean secondary FEC was not significantly different from unity. Testing under standardized conditions in pens did not result in consistently higher heritabilities than testing immunologically primed lambs at pasture. Repeated measurement in a breeding programme offers little additional benefit, except when lambs have had ample prior experience of parasite infection, with the two measures separated by an anthelmintic treatment. If an objective of a Merino breeding programme is to reduce FEC under field conditions, then using one measure in the field, approximately 3 to 5 weeks after a secondary artificial infection, is likely to lead to long-term progress.

Resistance and resilience to gastro-intestinal nematode parasites and relationships with productivity of Red Maasai, Dorper and Red Maasai ✕ Dorper crossbred lambs in the sub-humid tropics

Resistance and resilience to naturally acquired gastro-intestinal (GI) nematode parasite infections (predominantly Haemonchus contortus) were studied in 1785 lambs born over six lambings (1991 to 1996) consisting of 212 Red Maasai, 311 Dorper and 1262 crossbred (Red Maasai-Dorper) lambs in the sub-humid coastal region of Kenya. These lambs were the progeny of 41 Dorper and 35 Red Maasai rams. Live weights (LWT), blood packed cell volume (PCV) and faecal egg counts (FEC) were recorded at 1- to 2-monthly intervals from birth until the lambs were about one year of age. Red Maasai were more resistant and resilient post weaning to infections with GI nematodes than Dorper lambs as shown by their significantly lower FEC and their significantly higher PCV, respectively. An increasing proportion of Red Maasai genes in the crossbred lambs was associated with decreased FEC and higher PCV, but there was no heterosis for logarithm-transformed FEC (LFEC) or PCV. From one month of age Red Maasai lambs were significantly lighter than Dorper lambs by about 1 kg, but Red Maasai lambs had significantly lower lamb mortality rate from birth to 12 months of age (proportionately 0·30 and 0·66, respectively). Heritability estimates from a repeated measures analysis for records taken at 6 and 8 months of age were 0·14 (s.e. 0·05) for PCV from an animal model and 0·12 (s.e. 0·05) for LFEC from a sire model. The heritability estimate for LFEC from a repeated measures analysis including the four measurements recorded between 6 and 12 months of age was significantly higher (P < 0·05) for Dorper-sired lambs (0·15, s.e. 0·05 for an animal model and 0·19, s.e. 0·07 for a sire model) than for Red Maasai-sired lambs (0·00 and 0·01, s.e. 0·02). The phenotypic and genetic correlations between PCV and LFEC were moderately to highly negative and averaged –0·34 and –0·81, respectively. None of the genetic correlation estimates between LWT and PCV and LWT and LFEC for lambs post weaning were significantly different from zero. The heritability estimates for PCV and LFEC have important implications for within-breed genetic improvement programmes: for the Red Maasai, improvement should concentrate on resilience (e.g. selection for high PCV); for the Dorper, selection should be feasible for both improved resistance (low FEC) and resilience (high PCV).

Genetic resistance to gastro-intestinal nematode parasites in Galla and Small East African goats in the sub-humid tropics

A study was carried out from 1992 to 1996 to compare the resistance to naturally acquired gastro-intestinal (GI) nematode parasite infections (predominantly Haemonchus contortus) of Galla and Small East African goats in the sub-humid coastal region of Kenya. A total of 204 Galla and 349 Small East African (SEA) kids were born from five kiddings. These were the progeny of 18 Galla and 17 SEA bucks. Live weights (LWT), blood packed-cell volume (PCV) and faecal egg count (FEC) were recorded at 1- to 2-month intervals from birth to about 14 months of age. The SEA kids were more resistant to GI nematode parasites than Galla kids as shown by their significantly lower FEC (P< 0·001) in the post-weaning period (8- to 14-month-old kids) and lower mortality from birth to 14 months of age (P< 0·05). There was no significant (P> 0·05) breed effect on PCV, but Galla kids were significantly heavier (P< 0·001) at all measurement times between birth and 14 months of age. Heritability estimates for LWT, PCV and FEC at the different sampling times were characterized by high standard errors. Heritability estimates for records taken at 4·5 and 8 months of age from a repeated measures analysis were 0·18 (s.e.0·08) for PCV and 0·13 (s.e.0·07) for logarithm-transformed FEC. The phenotypic and genetic correlation estimates between PCV and LFEC were moderately to highly negative and averaged –0·36 and –0·53, respectively. The results are discussed in relation to the limited evidence for resistance to GI nematode infections in goats and compared with the much stronger evidence for resistance in sheep.

Selection of dairy sheep in Greece for parasitic nematode resistance: defining the aggregate genotype and evaluating selection schemes

The effects on genetic and economic responses of adding faecal egg count (FEC) in the aggregate genotype of dairy sheep in Greece were investigated. The extra responses obtained in the full aggregate genotype were expressed as a percentage change of the responses in terms of genetic gain, profit and selection response of single traits before adding the trait. The initial aggregate genotype included the traits milk fat yield (FY) and number of lambs weaned per ewe per year (NLW). Inclusion of FEC in the aggregate genotype resulted always in increased genetic gain and profit. The extra responses from adding the FEC in the index selection were variable and often very large, depending on the parameters varied i.e. the economic weight of FEC and the genetic correlation of FEC with the other production traits. For a wide range in the size of the genetic correlations between FEC and other traits, gains of FEC and no appreciable losses of responses for FY and NLW were predicted when FEC accounted proportionately for 0·10 to 0·20 of the total monetary genetic deviation. While FEC showed a wide range of change, selection responses of FY and NLW remained remarkably insensitive under various weightings of FEC and different genetic correlations of FEC with the production traits. The genetic and economic efficiency of alternative selection schemes were also evaluated. A two-stage selection procedure involving preliminary selection of rams on dam’s FEC, FY, NLW and on their own FEC and final culling on progeny’s FEC, FY and NLW was predicted to be the most efficient in both genetic and economic terms. Female replacements should be selected on dam’s FEC, FY and NLW (first stage) and their own FEC, FY and NLW (second stage). When repeated measurements of FEC are taken, the recommended number of FEC measurements was found to be 4.

Rumen fluke in Irish sheep: prevalence, risk factors and molecular identification of two paramphistome species

BACKGROUND

Rumen flukes are trematode parasites found globally; in tropical and sub-tropical climates, infection can result in paramphistomosis, which can have a deleterious impact on livestock. In Europe, rumen fluke is not regarded as a clinically significant parasite, recently however, the prevalence of rumen fluke has sharply increased and several outbreaks of clinical paramphistomosis have been reported. Gaining a better understanding of rumen fluke transmission and identification of risk factors is crucial to improve the control of this parasitic disease. In this regard, a national prevalence study of rumen fluke infection and an investigation of associated risk factors were conducted in Irish sheep flocks between November 2014 and January 2015. In addition, a molecular identification of the rumen fluke species present in Ireland was carried out using an isolation method of individual eggs from faecal material coupled with a PCR. After the DNA extraction of 54 individual eggs, the nuclear fragment ITS-2 was amplified and sequenced using the same primers.

RESULTS

An apparent herd prevalence of 77.3 % was determined. Several risk factors were identified including type of pasture grazed, regional variation, and sharing of the paddocks with other livestock species. A novel relationship between the Suffolk breed and higher FEC was reported for the first time. The predominant rumen fluke species found was C. daubneyi. Nevertheless, P. leydeni was unexpectedly identified infecting sheep in Ireland for the first time.

CONCLUSIONS

An exceptionally high prevalence of rumen fluke among Irish sheep flocks has been highlighted in this study and a more thorough investigation is necessary to analyse its economic impact. The isolation of individual eggs coupled with the PCR technique used here has proven a reliable tool for discrimination of Paramphistomum spp. This technique may facilitate forthcoming studies of the effects of paramphistomosis on livestock production. The most noteworthy finding was the identification of P. leydeni affecting sheep in Ireland, however further studies are required to clarify its implications. Also, a significant relationship between Suffolk breed and a heavier infection was found, which can be used as a starting point for future research on control strategies of rumen fluke infection.

Evaluation of Kumaon hill goats for resistance to natural infection with gastrointestinal nematodes

The present study deals with the investigation of different degrees of genetic resistance/resilience of Uttarakhand hill goats to natural infection with gastrointestinal nematodes in order to introduce into breeding schemes. Animals were naturally infected with Haemonchus contortus, Teladorsagia circumcincta, Oesophagostomum spp. and Trichostrongylus spp. Faecal egg counts (FEC) were carried out every month for a period of 1 year and blood samples were collected every third month for the determination of indicator traits such as FEC, packed cell volume (PCV) and haemoglobin (Hb). The mean egg per gram (EPG), PCV and Hb were 1,579.6 ± 346, 35.12 ± 1.1 and 8.7 ± 0.2, respectively. The goats were divided into three groups (<800, 801-2,000 and >2,000) based on EPG. The EPG showed a negative correlation with both Hb and PCV (P < 0.01). Therefore, it was concluded that the Hb and PCV value would decrease, if EPG increases.

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 Pathophysiology, Ecology and Epidemiology of Haemonchus contortus Infection in Small Ruminants

The parasitic nematode Haemonchus contortus occurs commonly in small ruminants, and it is an especially significant threat to the health and production of sheep and goats in tropical and warm temperate zones. The main signs of disease (haemonchosis) relate to its blood-feeding activity, leading to anaemia, weakness and frequently to deaths, unless treatment is provided. Due to the high biotic potential, large burdens of H. contortus may develop rapidly when environmental conditions favour the free-living stages, and deaths may occur with little prior warning. More chronic forms of haemonchosis, resulting in reduced animal production and eventually deaths, occur with smaller persistent infections, especially in situations of prolonged, poor nutrition. The global distribution of the main haemonchosis-endemic zones is consistent with the critical requirements of the egg and larval stages of H. contortus for moisture and moderate to relatively warm temperatures, but the seasonal propensity for hypobiosis (inhibition of the fourth-stage larvae within the host) largely explains the common, though sporadic, outbreaks of haemonchosis in arid and colder environments. The wide climatic distribution may also reflect the adaptation of local isolates to less favourable ecological conditions, while an apparent increase in the prevalence of outbreaks in environments not previously considered endemic for haemonchosis - especially cold, temperate zones - may be attributable to climatic changes. Although the risk of haemonchosis varies considerably on a local level, even where H. contortus is endemic, the extensive range of ecological investigations provides a sound basis for predictions of the relative geographical and seasonal risk in relation to climatic conditions.

Diagnosis, Treatment and Management of Haemonchus contortus in Small Ruminants

Haemonchus contortus is a highly pathogenic, blood-feeding nematode of small ruminants, and a significant cause of mortalities worldwide. Haemonchosis is a particularly significant threat in tropical, subtropical and warm temperate regions, where warm and moist conditions favour the free-living stages, but periodic outbreaks occur more widely during periods of transient environmental favourability. The clinical diagnosis of haemonchosis is based mostly on the detection of anaemia in association with a characteristic epidemiological picture, and confirmed at postmortem by the finding of large numbers of H. contortus in the abomasum. The detection of impending haemonchosis relies chiefly on periodic monitoring for anaemia, including through the 'FAMACHA' conjunctival-colour index, or through faecal worm egg counts and other laboratory procedures. A range of anthelmintics for use against H. contortus is available, but in most endemic situations anthelmintic resistance significantly limits the available treatment options. Effective preventative programmes vary depending on environments and enterprise types, and according to the scale of the haemonchosis risk and the local epidemiology of infections, but should aim to prevent disease outbreaks while maintaining anthelmintic efficacy. Appropriate strategies include animal management programmes to avoid excessive H. contortus challenge, genetic and nutritional approaches to enhance resistance and resilience to infection, and the monitoring of H. contortus infection on an individual animal or flock basis. Specific strategies to manage anthelmintic resistance centre on the appropriate use of effective anthelmintics, and refugia-based treatment schedules. Alternative approaches, such as biological control, may also prove useful, and vaccination against H. contortus appears to have significant potential in control programmes.

Population genetic structure of Ascaridia galli of extensively raised chickens of South Africa

Ascaridia galli is one of the most common nematode affecting chickens. This study characterized A. galli parasites collected from South African village chickens of Limpopo (n=18) and KwaZulu-Natal (n=22) provinces using the 510bp sequences of cytochrome C oxidase subunit 1 gene of the mitochondrial DNA. Fourteen and 12 polymorphic sites were observed for Limpopo and KwaZulu-Natal sequences, respectively. Six haplotypes were observed in total. Haplotype diversity was high and ranged from 0.749 for Limpopo province to 0.758 for KwaZulu-Natal province isolates. There was no genetic differentiation between A. galli from Limpopo and KwaZulu-Natal provinces. The six South African haplotypes were unique compared to those published in the GeneBank sampled from Hy-line chickens raised under organic farming in Denmark. The utility of cytochrome C oxidase subunit 1 gene as a potential genetic marker for studying A. galli in village chicken populations is presented.

Identification of novel loci associated with gastrointestinal parasite resistance in a Red Maasai x Dorper backcross population

Gastrointestinal (GI) parasitic infection is the main health constraint for small ruminant production, causing loss of weight and/or death. Red Maasai sheep have adapted to a tropical environment where extreme parasite exposure is a constant, especially with highly pathogenic Haemonchus contortus. This breed has been reported to be resistant to gastrointestinal parasite infection, hence it is considered an invaluable resource to study associations between host genetics and resistance. The aim of this study was to identify polymorphisms strongly associated with host resistance in a double backcross population derived from Red Maasai and Dorper sheep using a SNP-based GWAS analysis. The animals that were genotyped represented the most resistant and susceptible individuals based on the tails of phenotypic distribution (10% each) for average faecal egg counts (AVFEC). AVFEC, packed cell volume (AVPCV), and live weight (AVLWT) were adjusted for fixed effects and co-variables, and an association analysis was run using EMMAX. Revised significance levels were calculated using 100,000 permutation tests. The top five significant SNP markers with - log10 p-values >3.794 were observed on five different chromosomes for AVFEC, and BLUPPf90/PostGSf90 results confirmed EMMAX significant regions for this trait. One of these regions included a cluster of significant SNP on chromosome (Chr) 6 not in linkage disequilibrium to each other. This genomic location contains annotated genes involved in cytokine signalling, haemostasis and mucus biosynthesis. Only one association detected on Chr 7 was significant for both AVPCV and AVLWT. The results generated here reveal candidate immune variants for genes involved in differential response to infection and provide additional SNP marker information that has potential to aid selection of resistance to gastrointestinal parasites in sheep of a similar genetic background to the double backcross population.

Current status for gastrointestinal nematode diagnosis in small ruminants: where are we and where are we going?

Gastrointestinal nematode (GIN) parasites pose a significant economic burden particularly in small ruminant production systems. Anthelmintic resistance is a serious concern to the effective control of GIN parasites and has fuelled the focus to design and promote sustainable control of practices of parasite control. Many facets of sustainable GIN parasite control programs rely on the ability to diagnose infection both qualitatively and quantitatively. Diagnostics are required to determine anthelmintic efficacies, for targeted treatment programs and selection of animals for parasite resistant breeding. This review describes much of the research investigated to date to improve the current diagnostic for the above practices which is based on counting the number of parasite eggs in faeces.

A Prototype Tool to Enable Farmers to Measure and Improve the Welfare Performance of the Farm Animal Enterprise: The Unified Field Index

Schemes for the assessment of farm animal welfare and assurance of welfare standards have proliferated in recent years. An acknowledged short-coming has been the lack of impact of these schemes on the welfare standards achieved on farm due in part to sociological factors concerning their implementation. Here we propose the concept of welfare performance based on a broad set of performance attributes of an enterprise and describe a tool based on risk assessment and benchmarking methods for measuring and managing welfare performance. The tool termed the Unified Field Index is presented in a general form comprising three modules addressing animal, resource, and management factors. Domains within these modules accommodate the principle conceptual perspectives for welfare assessment: biological functioning; emotional states; and naturalness. Pan-enterprise analysis in any livestock sector could be used to benchmark welfare performance of individual enterprises and also provide statistics of welfare performance for the livestock sector. An advantage of this concept of welfare performance is its use of continuous scales of measurement rather than traditional pass/fail measures. Through the feedback provided via benchmarking, the tool should help farmers better engage in on-going improvement of farm practices that affect animal welfare.

Genetic parameters for growth and faecal worm egg count following Haemonchus contortus experimental infestations using pedigree and molecular information

Background

Haemonchosis is a parasitic disease that causes severe economic losses in sheep industry. In recent years, the increasing resistance of the parasite to anthelmintics has raised the need for alternative control strategies. Genetic selection is a promising alternative but its efficacy depends on the availability of genetic variation and on the occurrence of favourable genetic correlations between the traits included in the breeding goal. The objective of this study was twofold. First, to estimate both the heritability of and the genetic correlations between growth traits and parasite resistance traits, using bivariate linear mixed animal models, from the phenotypes and genotypes of 1004 backcross lambs (considered as a single population), which underwent two subsequent experimental infestations protocols with Haemonchus contortus. Second, to compare the precision of the estimates when using two different relationship matrices: including pedigree information only or including also SNP (single nucleotide polymorphism) information.

Results

Heritabilities were low for average daily gain before infestation (0.10 to 0.15) and average daily gain during the first infestation (0.11 to 0.16), moderate for faecal egg counts during the first infestation (0.21 to 0.38) and faecal egg counts during the second infestation (0.48 to 0.55). Genetic correlations between both growth traits and faecal egg count during the naïve infestation were equal to zero but the genetic correlation between faecal egg count during the second infestation and growth was positive in a Haemonchus contortus free environment and negative in a contaminated environment. The standard errors of the estimates obtained by including SNP information were smaller than those obtained by including pedigree information only.

Conclusions

The genetic parameters estimates suggest that growth performance can be selected for independently of selection on resistance to naïve infestation. Selection for increased growth in a non-contaminated environment could lead to more susceptible animals with long-term exposure to the infestation but it could be possible to select for increased growth in a contaminated environment while also increasing resistance to the long-term exposure to the parasite. The use of molecular information increases the precision of the estimates.

Alternativas para o controle de nematoides gastrintestinais de pequenos ruminantes

A criação de ovinos e caprinos depende de um manejo eficiente, devido, principalmente, ao prejuízo causado por parasitos em animais susceptíveis. Vários fatores colaboram para que os animais tolerem as infecções parasitárias, como: genética, nutrição, estado fisiológico e idade. O grave problema causado pela resistência anti-helmíntica promoveu a difusão de técnicas alternativas de controle parasitário. Dentre essas novas estratégias incluem-se a adoção do tratamento parcial seletivo com o método FAMACHA, fitoterapia, controle biológico com o uso de fungos nematófagos e estratégias que ainda necessitam de mais dados como a homeopatia, a diluição da resistência com a introdução de parasitos sensíveis e a combinação de produtos químicos sem efeito antiparasitário. O objetivo central destes métodos é reduzir o uso de antiparasitários, retardando o desenvolvimento da resistência, e promover melhor utilização de produtos ainda eficazes na propriedade e de novos produtos que venham a ser lançados. Este artigo abordará as técnicas descritas acima para o controle de nematoides de pequenos ruminantes e é direcionado aos técnicos interessados em ampliar seu conhecimento sobre os mecanismos de resistência dos parasitos aos anti-helmínticos e de alternativas ao uso desses produtos.

The immunology and genetics of resistance of sheep to Teladorsagia circumcincta

Teladorsagia circumcincta is one of the most economically important gastrointestinal nematode parasites of sheep in cool temperate regions, to which sheep show genetically-varying resistance to infection. This is a very common parasite and viable sheep production requires the extensive use of anthelmintic drugs. However, the emergence of drug-resistant parasites has stimulated the search for alternative control strategies to curb production losses. Lambs become infected soon after weaning and begin to control parasite burden within 8-10 weeks of continual infection. This control is an acquired characteristic mediated by the development of parasite-specific antibodies. This paper describes the immunology associated with resistance and susceptibility, focussing on differential T cell activation that regulates the production of specific effector mechanisms. It continues by summarizing the methods used to identify genes that could be exploited as molecular markers of selection for resistance. In particular it focusses on the link between understanding the molecular immunology of infection and the identification of candidate genes for selection.

Dynamics of infestation of tracers lambs by gastrointestinal helminths under a traditional management system in the North of Tunisia

The authors present a survey of gastrointestinal helminths of sheep on permanent pastures in the extreme north region of Tunisia (Mediterranean climate). Dynamic infestation of animals has been monitored by using batches of three tracer lambs introduced each two months during 2004 and 2005. These lambs were kept in the pens of veterinary school of Sidi Thabet (Tunisia) during three months and then necropsied. Faecal and blood samples were took from tracer lambs each two months during the whole period, and from animal flock only during 2004. The main helminth genera encountered were Trichostrongylus spp., Teladorsagia spp., Strongyloides papillosus and Anoplocephalidea; occasionaly were found Nematodirus, Oesophagostomum, Chabertia, Cooperia, Trichuris and Paramphistomum. The egg count of the ewes and lambs in the flock showed two peaks. For both ewes and lambs there is a gradual increase from January with a peak in May-June. This first peak is considered to be due to acquisition of infective larvae during the rainy and cold season, as evident from the worm burdens of tracer lambs. The second peak was exclusively observed in ewes during late autumn-early winter (November-December); it has two origins: infestation by third larvae stage and the periparturient rise. The worm burdens of tracer lambs showed that there was a gradual accumulation of nematodes from September-October, reaching a peak in March-April; a very low or naught infection is reported during the dry period (July-August). Infection by Anoplocephalidea was higher during the dry season. This study is primordial for a comprehensive control programme implementation against gastrointestinal helminths.

Genetic parameters for resistance to trichostrongylid infection in dairy sheep

In sheep, the traditional chemical control of gastrointestinal nematode (GIN) parasites with anthelmintics has led to the widespread development of anthelmintic resistance. The selection of sheep with enhanced resistance to GIN parasites has been suggested as an alternative strategy to develop sustainable control of parasite infections. Most of the estimations of the genetic parameters for sheep resistance to GIN parasites have been obtained from young animals belonging to meat- and/or wool-specialised breeds. We present here the estimated genetic parameters for four parasite resistance traits studied in a commercial population of adult Spanish Churra dairy ewes. These involved two faecal egg counts (FECs) (LFEC0 and LFEC1) and two serum indicator traits, the anti-Teladorsagia circumcincta fourth stage larvae IgA (IgA) and the pepsinogen (Peps) levels. In addition, this study has allowed us to identify the environmental factors influencing parasite resistance in naturally infected Spanish Churra sheep and to quantify the genetic component of this complex phenotype. The heritabilities estimated for the two FECs analysed (0.12 for LFEC0 and 0.09 for LFEC1) were lower than those obtained for the examined serum indicators (0.19 for IgA and 0.21 for Peps). The genetic correlations between the traits ranged from 0.43 (Peps-IgA) to 0.82 (LFEC0-LFEC1) and were higher than their phenotypic counterparts, which ranged between 0.07 and 0.10. The heritabilities estimated for the studied traits were lower than previously reported in lambs. This may be due to the differences in the immune mechanisms controlling the infection in young (antibody reactions) and adult (hypersensitivity reactions) animals/sheep. In summary, this study demonstrates the presence of heritable variation in parasite resistance indicator traits in the Churra population studied, which suggests that genetic improvement is feasible for this complex trait in this population. However, further studies in which the experimental variables are controlled as much as possible are needed to identify the best trait that could be measured routinely in adult sheep as an indicator of parasite resistance.

Markers/parameters for the evaluation of natural resistance status of small ruminants against gastrointestinal nematodes

The high prevalence of anthelmintic-resistant gastrointestinal nematodes (GINs) throughout the world has led to the need for alternative worm control strategies. One of the possible substitutes to reduce the problems of drug resistance and residue is the evaluation/breeding of small ruminants for greater resistance to the GINs (organically produced), which in turn would be a helpful tool to predict the performance of an animal. At present, the existing diversity in the genetic potential to resist/tolerate GINs infection both within and between breeds has been validated. Successful selection of animals to define the genotype and identified resistance is related to the employed markers. A number of phenotypic traits such as faecal egg count (FEC), worm burden, serum antibodies, peripheral eosinophilia, packed cell volume, live weight, serum protein and albumin concentrations have been used for this purpose both in natural and artificial infections. Relatively resistant/tolerant animals have also been found to have mastocytosis, globule leucocytes, high levels of histamine and immunoglobulin (Ig) A and IgE concentrations. Of these traits, the principal and most practical measurement used to assess resistance status in animals undergoing similar parasite challenges is FEC. FEC has a positive/negative correlation with other biochemical, cellular and immunological parameters; however, the reliability of individual trial is often questioned and valuable information regarding the genetic makeup can be obtained from pooled data of a large number of trials and parameters. This paper covers all the aspects reported in the literature on various parameters considered to evaluate the resistance status of a range of small ruminant breeds.

Economic values of body weight, reproduction and parasite resistance traits for a Creole goat breeding goal

A specific breeding goal definition was developed for Creole goats in Guadeloupe. This local breed is used for meat production. To ensure a balanced selection outcome, the breeding objective included two production traits, live weight (BW11) and dressing percentage (DP) at 11 months (the mating or selling age), one reproduction trait, fertility (FER), and two traits to assess animal response to parasite infection: packed cell volume (PCV), a resilience trait, and faecal worm eggs count (FEC), a resistance trait. A deterministic bio-economic model was developed to calculate the economic values based on the description of the profit of a Guadeloupean goat farm. The farm income came from the sale of animals for meat or as reproducers. The main costs were feeding and treatments against gastro-intestinal parasites. The economic values were 7.69€ per kg for BW11, 1.38€ per % for FER, 3.53€ per % for DP and 3 × 10(-4)€ per % for PCV. The economic value for FEC was derived by comparing the expected profit and average FEC in a normal situation and in an extreme situation where parasites had developed resistance to anthelmintics. This method yielded a maximum weighting for FEC, which was -18.85€ per log(eggs per gram). Alternative scenarios were tested to assess the robustness of the economic values to variations in the economic and environmental context. The economic values of PCV and DP were the most stable. Issues involved in paving the way for selective breeding on resistance or resilience to parasites are discussed.

Livestock Helminths in a Changing Climate: Approaches and Restrictions to Meaningful Predictions

Climate change is a driving force for livestock parasite risk. This is especially true for helminths including the nematodes Haemonchus contortus, Teladorsagia circumcincta, Nematodirus battus, and the trematode Fasciola hepatica, since survival and development of free-living stages is chiefly affected by temperature and moisture. The paucity of long term predictions of helminth risk under climate change has driven us to explore optimal modelling approaches and identify current bottlenecks to generating meaningful predictions. We classify approaches as correlative or mechanistic, exploring their strengths and limitations. Climate is one aspect of a complex system and, at the farm level, husbandry has a dominant influence on helminth transmission. Continuing environmental change will necessitate the adoption of mitigation and adaptation strategies in husbandry. Long term predictive models need to have the architecture to incorporate these changes. Ultimately, an optimal modelling approach is likely to combine mechanistic processes and physiological thresholds with correlative bioclimatic modelling, incorporating changes in livestock husbandry and disease control. Irrespective of approach, the principal limitation to parasite predictions is the availability of active surveillance data and empirical data on physiological responses to climate variables. By combining improved empirical data and refined models with a broad view of the livestock system, robust projections of helminth risk can be developed.