A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge

This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A short-term divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following artificial and natural infection were 0.49 and 0.70 respectively within a period of one week, and 0.22 and 0.41 respectively for periods separated by intervals of 7 weeks; the heritabilities of the single egg count were 0.22 and 0.38 respectively. The genetic correlation was 0.87: the FEC recorded under natural or artificial infection appear to depend on the same genetic potential

Gastrointestinal strongyles of ruminants : mechanisms of anthelmintic resistance and consequences on their management

The management of gastrointestinal strongyle infestations in ruminants relies mostly on anthelmintics. Only three chemical families are available, and gastrointestinal strongyles resistance is increasing. The resistance mechanisms are relatively well known for benzimidazoles (involving one gene with two alleles), whereas the genetic determinism of the resistance to macrocyclic lactones or imidazothiazoles (levamisole) is still poorly understood, but probably involves multigenic regulation. A double approach (candidate genes and transcriptomic) is proposed for levamisole resistance and the first results are presented. It is very important to understand resistance mechanisms to reduce their occurrences. Examples with benzimidazoles are presented to describe interactions between the type of genetic mechanism and the speed with which resistance appears and expands, the efficacy of selective pressure by treatments, and the role of refugia.La gestion des infestations du tube digestif par les strongles chez les ruminants est essentiellement assurée par les traitements anthelminthiques. Seules trois familles chimiques sont disponibles et des phénomènes de résistance à ces produits sont apparus chez les strongles gastro-intestinaux. Les mécanismes de résistance concernant la famille des benzimidazoles sont relativement bien établis (un gène avec deux allèles est impliqué), alors que pour la famille des lactones macrocycliques ou celle des imidazothiazoles (lévamisole), les déterminismes génétiques, encore peu connus, sont sans doute multigéniques. Une double approche (« gènes candidats » et transcriptomique) est proposée pour le lévamisole et les premiers résultats sont présentés. La compréhension des mécanismes d'action est très importante pour tenter de réduire l'apparition de résistance. Des exemples concernant les benzimidazoles sont utilisés pour décrire l'interaction entre le type de mécanisme de résistance et la vitesse d'apparition et de diffusion de la résistance, l'efficacité des pressions sélectives par les traitements et le rôle des refuges

Global fine-resolution data on springtail abundance and community structure

Springtails (Collembola) inhabit soils from the Arctic to the Antarctic and comprise an estimated ~32% of all terrestrial arthropods on Earth. Here, we present a global, spatially-explicit database on springtail communities that includes 249,912 occurrences from 44,999 samples and 2,990 sites. These data are mainly raw sample-level records at the species level collected predominantly from private archives of the authors that were quality-controlled and taxonomically-standardised. Despite covering all continents, most of the sample-level data come from the European continent (82.5% of all samples) and represent four habitats: woodlands (57.4%), grasslands (14.0%), agrosystems (13.7%) and scrublands (9.0%). We included sampling by soil layers, and across seasons and years, representing temporal and spatial within-site variation in springtail communities. We also provided data use and sharing guidelines and R code to facilitate the use of the database by other researchers. This data paper describes a static version of the database at the publication date, but the database will be further expanded to include underrepresented regions and linked with trait data.</p

Determining the best sheep protective strategy to combat infection by the nematode <em>Haemonchus contortus</em>: is resistance futile ?

International audienceThe gastrointestinal nematode Haemonchus contortus represents one of the most significant threat to ruminant production systems worldwide. Control is now looking towards selectively breeding sheep to meet production targets in the presence of such a threat. Breeding sheep which are resistant to the infection has been presented as a mean to reduce parasite-induced production losses. Yet there is mounting evidence to suggest that the protection mechanisms responsible for host resistance come at a cost and that immune-mediated pathology may render the breeding strategy counter-productive. Breeding sheep for resilience to the effects of H. contortus infection has instead been proposed as an alternative breeding strategy in which to minimize potential immunopathological negations on production. This study investigates the impacts a primary H. contortus infection confers on the body condition of sheep hosts under three different hostresistance strategies; where H. contortus has: no success (Martinik Black Belly ewes, n=25), low success (Martinik Black Belly rams, n=25) and high success (Romane rams, n=16). The sheep infection burden was evaluated by means of faecal egg counts (FEC). Their condition was evaluated using haematocrit as an indicator of anaemia, temperature as indicator of pain and relative weight gains. It then goes on to disentangle the worsening of condition and pain attributed to the parasite and to the cost of protection against the parasite. The study goes on to disentangle the relative parasite-induced and host-induced effects on the worsening of host condition. . The results suggest that resistance is not a costly strategy as long is it is complete as observed in Black Belly ewes: no infection, minimal impacts on anaemia or weight. Being susceptible to infection came at greater cost to the host condition as shown in the Romane rams: high FEC and lowest haematocrit levels by the end of the study. The most costly strategy was that of Black Belly rams in maintaining low levels of infection: low FEC, greatest decreases in body temperature (thereby possibly pain), and low haematocrit values These results carry significant implications for the selection criteria used in selective breeding and also provide further insight into the sheep costs of fighting a H. contortus infection

Haemonchus contortus Adopt Isolate-Specific Life History Strategies to Optimize Fitness and Overcome Obstacles in Their Environment: Experimental Evidence

International audienceGastrointestinal nematodes (GIN) use flexible life history strategies to maintain their fitness under environmental challenges. Costs incurred by a challenge to one life trait can be recouped by increasing the expression of subsequent life traits throughout their life cycle. Anticipating how parasites respond to the challenge of control interventions is critical for the long-term sustainability of the practice and to further ensure that the parasites withstand favourable adaptive responses. There is currently limited information on whether distinct populations of a GIN species respond to the same environmental challenge in a consistent manner, with similar alterations to their life history strategies or comparable fitness outcomes. This study compared the life history traits and experimental fitness of three distinct Haemonchus contortus isolates exposed to environmental challenges at both the parasitic (i.e., passage through resistant or susceptible sheep) and free-living (i.e., exposure to diverse climatic conditions) life stages. The key findings show that H. contortus maintain their fitness under challenge with isolate-specific alterations to their life history strategies. Further, partial exploration of the H. contortus isolates transcriptomes using cDNA-AFLP methods confirmed disparate expression profiles between them. These results bring fresh insights into our understanding of the non-genetic adaptive processes of GIN that may hinder the efficacy of parasite control strategies

Exploring the limitations of pathophysiological indicators used for targeted selective treatment in sheep experimentally infected with [i]Haemonchus contortus[/i]

Identifying which sheep to treat as part of a Targeted Selective Treatment approach to gastro-intestinal nematode control relies entirely on the efficacy of the indicators. Indicators such as FAMACHA© (anaemia), DISCO (diarrhea) and reductions in weight gains were designed specifically to reflect those sheep experiencing symptomatic consequences of infection. Using the gastro-intestinal nematode Haemonchus contortus as a model species, this study explored the utility and sensitivity of these indicators under controlled experimental conditions on 63 adult sheep. The potential effect of sheep with different H. contortus resistance phenotypes on indicator efficacy was compared in three different phenotypes, i.e. high (Blackbelly females), medium (Blackbelly rams) and low resistance (Romane rams). The potential effect of the H. contortus isolate on indicator efficacy was also explored by using four different isolates, with varying anthelmintic resistance capacities, to infect the sheep. We limited the study to the first month of infection to evaluate the interest of these indicators as an early predictive means for controlling infection. The pathophysiological indicators FAMACHA© and DISCO do not reflect infection intensity based on Faecal Egg Counts, nor do reductions in weight gains. FAMACHA© was however a good indicator of anaemia with strong correlations to haematocrit. There was little agreement among the three indicators to identify the same animals in need of treatment and even combining them did not increase their predictive value of infection intensity or relative host damage from infection. The indicator sensitivity was influenced by the H. contortus isolate and sheep resistance phenotype in which they were tested. One isolate was poorly infective but induced high levels of anaemia (FAMACHA©) and diarrhea (DISCO) compared to the three others. The FAMACHA© and DISCO had higher values in the sheep group with a medium resistance phenotype (Blackbelly rams) indicating higher levels of damage compared to the high and low resistance phenotypes. We conclude that there is no ‘one size fits all’ approach to the use of indicators for Targeted Selective Treatment and the indicators should be calibrated to farm-specific conditions to increase their efficacy

Les perspectives de thérapeutique adjuvantes ou alternatives pour la gestion des nématodes parasites d’équidés

DOSSIER : LA RÉSISTANCE AUX ANTHELMINTHIQUES CHEZ LES ÉQUIDÉSDans le contexte de l’émergence de la résistance aux anthelminthiques, le développement de stratégies alternatives semble indispensable.Ces stratégies restent, à l'heure actuelle, expérimentales et seront mises en pratique que dans quelques années.Les alternatives considérées portent sur la lutte biologique, par l'intermédiaire de champignons nématophages notamment.D'autres stratégies visant à augmenter la résistance de l'hôte, conférée par un vaccin ou par certains apports nutritionnels , ne semblent pas appropriées dans le cas des nématodoses gastro-intestinales.À l'interface de ces deux approches, le potentiel bioactif de certaines plantes pourrait conférer aux prairies et aux fourrages cultivés un rôle “pharmacologique” permettant de limiter la charge parasitaire des équidés

Les perspectives de thérapeutique adjuvantes ou alternatives pour la gestion des nématodes parasites d’équidés

DOSSIER : LA RÉSISTANCE AUX ANTHELMINTHIQUES CHEZ LES ÉQUIDÉSDans le contexte de l’émergence de la résistance aux anthelminthiques, le développement de stratégies alternatives semble indispensable.Ces stratégies restent, à l'heure actuelle, expérimentales et seront mises en pratique que dans quelques années.Les alternatives considérées portent sur la lutte biologique, par l'intermédiaire de champignons nématophages notamment.D'autres stratégies visant à augmenter la résistance de l'hôte, conférée par un vaccin ou par certains apports nutritionnels , ne semblent pas appropriées dans le cas des nématodoses gastro-intestinales.À l'interface de ces deux approches, le potentiel bioactif de certaines plantes pourrait conférer aux prairies et aux fourrages cultivés un rôle “pharmacologique” permettant de limiter la charge parasitaire des équidés

L'identification morphométrique des stades infestants des nématodes gastro-intestinaux chez les bovins

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Economical optimization of targeted selective drenching in horses

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