L. Gruner

Genetic resistance to gastrointestinal nematode parasites in Polish long-wool sheep.

A study was undertaken from 1991 to 1994 on a farm in southern Poland to evaluate the genetic parameters of resistance to gastrointestinal nematodes. The predominant species were Teladorsagia circumcincta and Haemonchus contortus. A total of 32 sires were evaluated, around 15 per year. Faecal egg counts were measured twice during the 4-month grazing season for lambs (total 659 lambs) and three times for their mothers (total 327 ewes). Infection levels were high during the first 2 years and low during the last 2 years. Using an animal model, the heritability of log10(epg+25) increased from 0.20 in August to 0.33 in September for lambs, and from 0.18 in May to 0.25 in September for ewes. The repeatability of ewe faecal egg count between years was 0.25. A genetic correlation of 0.58 was found between faecal egg count in ewes and in 6-7-month-old lambs. A negative genetic correlation (-0.61) was estimated between faecal egg count in September and daily weight gain of lambs from 70 days of age to the end of grazing season (7 months of age). The results confirm the feasibility of genetic selection of sheep for resistance to nematode parasites in an environment where T. circumcincta and H. contortus are the dominant species.

Immune response to Haemonchus contortus infection in susceptible (INRA 401) and resistant (Barbados Black Belly) breeds of lambs.

The immune responses to Haemonchus contortus were compared in studies in resistant Barbados Black Belly (BBB) and susceptible INRA 401 (INRA) breeds of lambs. The cytokine patterns indicated a Th2‐biased response in both breeds. A more persistent and elevated Th2 cytokine mRNA transcription and blood eosinophilia were noted in the BBB lambs. However, at days 4 and 30 post‐infection, abomasal recruitment of eosinophils and mast cells were similar between the two breeds. Following primary infections, the BBB demonstrated a substantially lower faecal egg count compared to the INRA lambs. Furthermore, worm counts at 4 and 30 days post‐infection, and adult female worm size and in utero egg counts 30 days after the first infection were significantly lower in the BBB than in the INRA breed. In the INRA breed, re‐infection caused a significant reduction in most parasitological parameters compared with those observed after the primary infection. A similar response was not observed in the BBB sheep. In conclusion, while the major driving force in the response to H. contortus infection is a Th2‐biased immunity in which the BBB showed its maximal performance during the primary infection, the INRA breed performed better after re‐infection compared to its response to first exposure.

Comparison of the resistance to sympatric and allopatric isolates of Haemonchus contortus of Black Belly sheep in Guadeloupe (FWI) and of INRA 401 sheep in France.

The resistance of a tropical breed of sheep towards the nematode parasite Haemonchus contortus (Hc) was compared to that of a European breed after artificial infection with the parasite following a 2 x 2 x 2 experimental design: two isolates (Hc Gua from Guadeloupe versus Hc Fra from France), two breeds each reared in their native habitats (Black Belly (BB) in Guadeloupe, FWI, INRA 401 reared in France), and two groups of lambs with differing infection status (one naive, i.e. infected for the first time during the experiment, and one primed, i.e. which had previously received doses of 5000 L3 on Days -35 and -32 before the infection during this experiment). Both groups were composed of 10 male lambs, which were 20 weeks of age when they were given a dose of 10,000 L3 of the relevant isolate on Day 0. Resistance was assessed by regular fecal egg counts (FECs) and blood samples, and worm counts were processed on Day 35 p.i. The FEC was lower in the BB than in INRA 401 lambs, lower in the primed than naive groups, and lower in Hc Fra than in Hc Gua. The eosinophil count remained unchanged in the naive INRA 401 groups, but increased in all the other groups. The hematocrit fell after infection, but the live weight was not affected by the infection. Worm burdens were 1868 and 5237 in the naive BB and INRA 401 groups, respectively, and 596 and 4835 in the primed BB and INRA 401 groups. The daily production of eggs per Hc Gua female worm was 1.5-fold that of Hc Fra. The number of worms had no effect on worm length or Hc in utero egg count in the BB sheep, but a positive and significant correlation between these two traits was seen in the INRA 401 lambs. These findings are indicative of innate resistance, and confirmed the high acquired resistance of the BB sheep to both sympatric and allopatric isolates of Hc. The regulation of worm population and fecundity differed in the BB and INRA 401 sheep.

A genome scan for QTL affecting resistance to Haemonchus contortus in sheep.

Gastrointestinal nematodes are one of the main health issues in sheep breeding. To identify loci affecting the resistance to Haemonchus contortus, a genome scan was carried out using 1,275 Romane × Martinik Black Belly backcross lambs. The entire population was challenged with Haemonchus contortus in 2 consecutive experimental infections, and fecal egg counts (FEC) and packed cell volumes were measured. A subgroup of 332 lambs with extreme FEC was necropsied to determine the total worm burden, length of female worms, sex ratio in the worm population, abomasal pH, and serum and mucosal G immunoglobulins (IgG) responses. Pepsinogen concentration was measured in another subset of 229 lambs. For QTL detection, 160 microsatellite markers were used as well as the Illumina OvineSNP50 BeadChip that provided 42,469 SNP markers after quality control. Linkage, association, and joint linkage and association analyses were performed with the QTLMAP software. Linkage disequilibrium (LD) was estimated within each pure breed, and association analyses were carried out either considering or not the breed origin of the haplotypes. Four QTL regions on sheep chromosomes (OAR)5, 12, 13, and 21 were identified as key players among many other QTL with small to moderate effects. A QTL on OAR21 affecting pepsinogen concentration exactly matched the pepsinogen (PGA5) locus. A 10-Mbp region affecting FEC after the 1st and 2nd infections was found on OAR12. The SNP markers outperformed microsatellites in the linkage analysis. Taking advantage of the LD helped to refine the locations of the QTL mapped on OAR5 and 13.

Evolution of nematode community in grazing sheep selected for resistance and susceptibility to Teladorsagia circumcincta and Trichostrongylus colubriformis: a 4-year experiment

Field trials were undertaken to compare nematode population dynamics in two experimental flocks of rams selected for high and for low faecal egg counts (FECs) following two doses with 20000 infective larvae, 12000 Teladorsagia circumcincta (Tcirc) and 8000 Trichostrongylus colubriformis (Tcol) separated by a treatment. The selection was done by dosing 200 ram lambs (INRA 401 breed) and FECs proceeded with egg identification on days 28 and 35 post-each-infection. The 30 lambs with the lowest FECs constituted the group of permanent resistant rams (R), the 30 with the highest values the group of susceptible ones (S). Each group grazed separated pastures from April to November, this during 4 consecutive years. The contamination (number of eggs deposited) was estimated every 3 weeks on each pasture. The larval populations was measured by successive groups of tracer lambs. The infection of the permanent rams was done by slaughtering eight R and S rams on mid and end of each grazing season. Each autumn, new R and S ram lambs were selected to complete the R and S groups before turning out in spring. On third year, a third species (Haemonchus contortus, Hcon) was added to compare its behaviour with the two others. The regulation of parasite populations were studied by comparing what happens in R rams and pasture to S ones. The selected R ram lambs had a FEC of Tcirc 50% lower than S ones. This induced a similar lowered pasture contamination, a 25% decrease of infective larval population in years 2 and 3, and the worm burdens in R rams were the half of that in S rams after 2 years. The FEC of Tcol was 75% lower at the selection and induced similar difference in pasture contamination, but 65 and 96% reduction in L3 population, respectively, after 1 and 2 years. The worm burden was reduced by 99%. Adding Hcon species during the third year, in year 4, the L3 population was half in R pasture compared with S one, and R rams had 60% less worms of this species than S ones. This selection without any drench prevent outbreaks observed in young tracer lambs on S pasture. The comparison of selected resistant rams to selected susceptible ones and not to unselected controls gave more rapid information about the tendency of the regulation of the communities of nematode parasites.

Accuracy of two methods for counting eggs of sheep nematode parasites

A comparative study was carried out on eight species of sheep gastrointestinal nematodes in order to compare the value of two techniques for egg counting: the classical McMaster technique with saturated magnesium sulfate solution and a technique of egg extraction from faeces and counting by total collection after three centrifugations. Efficiency of extraction from 10 g of faeces was 95.9 to 99.5% according to the species of parasite, whereas the number of eggs counted by the McMaster technique represented only 16.5% of the total eggs present in the faeces. Advantages inherent in the use of these techniques are discussed.

Faecal water content and egg survival of goat gastro-intestinal strongyles under dry tropical conditions in Guadeloupe

Faeces from naturally infected goats were deposited on a natural grassland during the dry season in Guadeloupe (French West Indies) at different times throughout the day. The grass was either 7 or 20–30 cm tall. After a period of between several hours and 7 days, the number of viable strongyle eggs and the faecal water content were measured. Faecal temperature was recorded continuously. Faecal temperature was >40°–45°C at midday and dehydration was rapid between 8 a.m. and 2 p.m. Egg mortality was greater on short than on tall grass and higher in morning than in evening deposits. Minimal faecal water content during the first 36 h explained the 74%, 55% and 38% mortality rate for eggs ofOesophagostomum columbianum (OC),Haemonchus contortus (HC) andTrichostrongylus colubriformis (TC), respectively. In all, 5%–22% of the eggs of the latter species remained viable in a state of anhydrobiosis after 7 days on the ground. A delay of only 2 days between goat departure and irrigation would be sufficient to ensure that >95% ofO. columbianum andH. contortus eggs and 70% ofT. colubriformis eggs are destroyed.

Effects of irrigation on appearance and survival of infective larvae of goat gastro-intestinal nematodes in guadeloupe (French West Indies)

In Guadeloupe (French West Indies), faeces from naturally infected goats were deposited during the dry season on three plots, irrigated with long (plot A) or short herbage (B) and non-irrigated with long herbage (C). Microclimatic data and the evolution of L3 population size in faeces, on soil surface and on herbage were followed over a period of 26 days. The initial nematode egg population was comprised of 58% Haemonchus contortus (HC), 25% Trichostrongylus colubriformis (TC) and 17% Oesophagostomum columbianum (OC). Temperature and water content varied in time and space (soil, faeces, herbage) from homogeneous in A to very heterogeneous in C. In A and B, population dynamics were similar with higher values of maxima in A. Larval peaks occurred on day 9 after deposition in faeces in plot A: 23.1, 39.1 and 17.2 L3/100 eggs, respectively for HC, TC and OC; the same day in soil: 1.9, 0.6 and 3.1 L3/100 eggs. On day 26 it remained less than 1 L3/100 eggs in both soil and herbage for the three species. In C, only TC larvae were observed coming, after rain, from eggs in which hatching had been delayed. It was difficult to separate the respective effects of temperature and water content on the development of the eggs, but irrigation gave favourable conditions for all eggs to develop into larvae. Pasture rotation with 28-35 days of regrowth should minimize the increased risk of infection for the goats due to irrigation.

Relative effect of temperature and moisture on the development of strongyle eggs to infective larvae in bovine pats in Argentina

To determine the most efficient microclimatic factors in bovine faeces that could explain the rate of development of parasitic nematode species, experimental pats were deposited in three locations (sun, shade and laboratory) in central-west Argentina during summer, autumn and winter seasons. Faecal water content (FWC) and temperature inside the pats were recorded during the duration of the experimental periods. The mean temperature and minimal values of FWC explained 54% of the variability of the rate of development of Haemonchus (third-stage larvae per 100 eggs) and mean maximal temperature and minimal FWC values were the two main factors regulating Cooperia development (R2 = 0.42). Rainfall was the third factor. No microclimatic component explained the development of Ostertagia in our experiments.

The length of strongylid nematode infective larvae as a reflection of developmental conditions in faeces and consequences on their viability

Abstract Isolates from eight gastro-intestinal nematode species of sheep, cattle and deer parasites were maintained in sheep and faecal cultures were processed at different temperatures (for four species) and moistures (for the eight species). For all the tested species, the third-stage larvae (L3) were longer at temperatures optimal for development and their length increased linearly with faecal moisture contents (FMC). These variations in length mainly concerned the volume of intestinal cells. The length of L3 had no consequence on their survival in water at room temperature (five species tested), but the short L3 migrated more slowly on agar gel than did the longer ones (verified for three species) and exsheathed more slowly (verified for two species). The establishment rate observed for short L3 of Teladorsagia circumcincta in lambs was lower than that seen for long L3 in three other lambs, but the developed worms were similar in length and fecundity. These results are relevant to our understanding of how the different species could adapt to and/or compensate for adverse conditions of development.