Faecal Nematode Egg Counts Research Articles

Drench-and-shift is a high-risk practice in the absence of refugia

AIM: To examine the effect of an anthelmintic treatment to lambs, followed immediately by a shift onto pastures with differing levels of larval contamination, on the development of anthelmintic resistance, in order to support recommendations to farmers regarding drench-and-shift practices for sustainable worm control. METHODS: Newly weaned Romney lambs (n=72) were dosed with third-stage infective larvae (L3) of two nematode parasite species, Teladorsagia (=Ostertagia) circumcincta and Trichostrongylus colubriformis, comprising benzimidazole-resistant and -susceptible isolates, calculated to yield, after treatment with albendazole, a 95% reduction in faecal nematode egg count (FEC). Once infections became patent (Day 0), lambs were randomised into nine groups of eight animals, treated with albendazole at the manufacturer's recommended dose rate, and moved to individual pastures each previously prepared to have one of three different levels of parasite larval infestation (Treatment 1 = low contamination, Treatment 2 = medium contamination, and Treatment 3 = high contamination), and grazed on those pastures before receiving a second treatment with albendazole at Day 47. Anthelmintic resistance status in each group of lambs was measured using FEC reduction (FECR) and egghatch assays (EHA) after the first anthelmintic treatment, and FECR after the second treatment. RESULTS: Egg-hatch assays demonstrated significant differences between treatments. The concentration of anthelmintic required to kill 50% of the eggs (LC50) for Treatment 1, comprising the least contaminated pastures, was significantly higher than for Treatments 2 and 3 on Days 33 and 40. Treatment 1 also had a significantly lower FECR at the final anthelmintic treatment, and significantly lower FEC than the other two treatments from Days 26 to 47. CONCLUSIONS: The results demonstrated that the populations of T. circumcincta and T. colubriformis in lambs treated with anthelmintic had significantly higher levels of albendazole resistance at the end of the grazing period in lambs moved onto pastures with relatively low levels of parasite contamination than those moved onto pastures with relatively higher contamination, confirming drench-and-shift onto ‘clean’ pasture as a high-risk practice for the selection for anthelmintic resistance. While this does not necessarily preclude the use of this practice it does emphasise the importance of taking appropriate remedial action to minimise the risk.

Characterization of immune responses against gastrointestinal nematodes in weaned lambs grazing willow fodder blocks

A 131-day rotational grazing experiment was conducted in the summer autumn of 2007/2008 to compare effects of feeding condensed tannin (CT)-containing willow ( Salix spp.) fodder blocks ( i.e., silvopastoral system) or perennial ryegrass ( Lolium perenne)/white clover ( Trifolium repens) control pasture upon the immune response to gastrointestinal nematode parasite infection in Romney weaned lambs. Groups of lambs ( n = 40) were allocated to either willow fodder blocks or control pasture; half of each group ( n = 20) were regularly-drenched with anthelmintic at approximately 21 day intervals, whilst the remaining 20 weaned lambs were not drenched unless pre-determined faecal nematode egg counts (FEC) were reached, when all weaned lambs in that group were drenched with anthelmintic ( i.e., trigger-drenching). Metabolizable energy and CT concentrations were higher in willow fodder versus pasture herbages. Weaned lambs grazing willow fodder blocks had lower live weight gain (92 g/day) and carcass weight (14.4 kg) than those grazing control pasture (134 g; 15.3 kg), with no effect of anthelmintic drenching. Regular anthelmintic treatment maintained similar and low FEC up to day 82, which then increased, whilst trigger-drenched lambs grazing willow fodder blocks had higher FEC than lambs grazing control pasture on three out of eight occasions. As judged by faecal larval cultures, grazing willow fodder blocks reduced the relative proportions of abomasal-dwelling parasites ( Haemonchus contortus and Teladorsagia spp.). Trigger-drenched willow fodder block-fed sheep had higher platelet, eosinophil, total white blood cell and lymphocyte counts, greater CD21 + and greater γδ (Gamma Delta) TCR + (T cell receptor) lymphocyte subsets than control pasture-fed sheep, and higher plasma levels of Immunoglobulin A (IgA) specific for carbohydrate larval antigen (CarLa) on day 105 (P <0.001). None of these parameters were affected by grazing treatment in regularly-drenched lambs. Higher immunological measurements in trigger-drenched lambs grazing willow fodder blocks could be due to higher larval intake and/or to the effects of secondary compounds in willow fodder blocks priming the immune system. Further research is required to separate these effects.

Estudo comparativo do sistema famacha entre caprinos e ovinos sob o mesmo manejo produtivo no sertão baiano

This study evaluates the FAMACHA method used by sheep and goat producers in the semi-arid region of Bahia, Brazil. A total of 60 crossbred Anglo Nubian goats and 60 crossbred sheep (Santa Ines x Dorper) were assessed. Animals were aged 4-6 months and had an average weight of 31,4 and 27,5 kg, respectively. Both groups were raised in a semi-extensive system and shared the same stalls in a farm located in the city of Feira de Santana from July to December 2008. Mean and standard derivations of the nematode fecal egg counts (EPG) in goats were 1756 ± 670, 2013 ± 942, and 2013 ± 942 (FAMACHA 2, 3 and 4), whereas average EPG values in sheep were 335 ± 248, 537 ± 487, and 1736 ± 2263 (FAMACHA 1, 2 and 3). Packed cell volumes (PCV) in goats were 27 ± 2,20, 25 ± 2,49, and 21 ± 3,55 (FAMACHA 2, 3 and 4), and PVC in sheep were 33 ± 2,17, 32 ± 1,66, and 26 ± 5,36 (FAMACHA 1, 2 and 3). Therefore, values of EPG and PCV were significantly different as regards FAMACHA scores of goats and sheep raised in the same conditions.

Epidemiology and effects of gastrointestinal nematode infection on milk productions of dairy ewes

66 Pampinta breed ewes were studied during milking to evaluate the infection and the effect of gastrointestinal nematode on milk production sheep system. Naturally infected ewes on pasture were randomly allocated to two groups: TG, suppressively treated group every four weeks with levamisole and UG, untreated group. Faecal nematode egg counts and larval differentiation were conducted monthly. Successive groups of worm free tracer lambs were grazed with ewes and then slaughtered for worm counts. Test-day milk yield of individual ewes was recorded and ewe machine-milking period length (MPL) were estimated. Faecal egg counts and tracer nematode numbers increased towards midsummer and declined sharply toward the end of the study. TG (188.0 +/- 60 liters) produced more (p < 0.066) milk liters than UG (171.9 +/- 52.2) and TG had significantly more extended (p < 0.041) MPL than those of UG. The present study showed that dairy sheep were negatively affected by worms, even when exposed to short periods of high acute nematode (mainly Haemonchus contortus) infection.

Effects of including chicory in perennial ryegrass–white clover leys on production and health in organic lambs

Two trials were conducted to examine the effect of chicory included in or as additional plots of the ryegrass–white clover pastures on growth, naturally acquired nematode infections and selectivity of chicory by lambs. In Experiment 1, 31 weaned Texel lambs (36 ± 7 kg) grazed either ryegrass–white clover (CTRL) or ryegrass–white clover–chicory pastures (CHIC). In Experiment 2, 30 weaned Shropshire lambs (32 ± 7 kg) grazed either ryegrass–white clover (CTRL) or ryegrass–white clover with access to small additional chicory plots, which corresponded to 3% (CHIC-LO) or 6% of the total grazing area (CHIC-HI). No consistent differences in live weight gain and nematode faecal egg counts were observed in lambs grazing the different pasture types. Sward height on the ryegrass–white clover–chicory pasture was higher than the ryegrass–white clover pasture in the period from the 21th August to October in Exp. 1 and in the period from July to mid August in Exp. 2. In Exp. 1 ewe lambs in CHIC performed better than ram lambs (197 ± 11 vs. 154 ± 13 g day − 1 ; P < 0.05 for ewe vs. ram lambs) whereas ram lambs performed best without chicory (190 ± 13 vs. 177 ± 11; P < 0.05 for ram vs. ewe lambs). The relative proportion of chicory eaten by lambs did not differ significantly from August to October and averaged 4.0%. Lambs showed a consistent aversion to chicory. It can be concluded that including chicory into a well-managed mixed sward of perennial ryegrass and white clover 1) improved herbage availability under conditions that are suboptimal for ryegrass/clover swards but 2) did not give consistent effects on growth performance or reduction of nematode infection levels of grazing lambs probably due to a low intake of chicory, as lambs avoided chicory in a mixed sward of high quality. The negative selection of chicory by lambs makes a strategic utilization of chicory's potential in a mixed sward difficult under relatively fertile soil conditions.

The use of targeted selective treatments against gastrointestinal nematodes in milking sheep and goats in Greece based on parasitological and performance criteria

This study compared the use of targeted selective treatment (TST) with systematic whole-flock treatments in 38 dairy sheep and goat farms in Greece. Criteria for individual treatments were either parasitological (nematode faecal egg count) or performance-based (body condition score or milk yield). The possible effect of treatment on resistance to benzimidazole anthelmintics was assessed using the Egg Hatch Test. Mean faecal egg counts decreased during the 12-month experimental period in all groups, and were lowest in the TST group treated according to faecal egg count ( P < 0.05). The number of sheep and goats treated by TST was reduced compared with systematic treatments. Mean thiabendazole-egg death dose 50 (TBZ-ED 50) values from all groups were similar at the beginning and end of the study ( P > 0.05), but significant variation in TBZ-ED 50 was noted over the study period in systematically treated goats ( P = 0.045). Third stage larvae belonging to the genera Teladorsagia, Trichostrongylus and Haemonchus were dominant throughout the experimental period in all flocks. It was concluded that the use of targeted selective treatment reduced the number of anthelmintic treatments to achieve a similar level of parasite control or animal production and may offer a viable option to combine animal production with effective parasite control in Greece.

Dietary impacts on the resistance of Merino lambs to Trichostrongylus colubriformis

AIM: To evaluate and compare the effects of a variety of diets on the resistance of young, lightweight Merino lambs to repeated low-dose infections of Trichostrongylus colubriformis. METHODS: Ninety-six 12-week-old lambs were fed balanced or unbalanced diets, and given primary (at 19 weeks of age) or both primary (at 12 weeks) and secondary (at 19 weeks) infections of T. colubriformis. Suboptimal diets were low in total intake, rumen undegradable protein, total protein, readily available carbohydrate or minerals, or supplemented with cod liver oil. Liveweight was monitored fortnightly, protection was assessed from worm counts at the end of the study (25 weeks) and faecal nematode egg counts (FEC) conducted weekly, and mast-cell response assessed at the conclusion of the study from concentration of mast-cell protease in the jejunum. Concentrations of glucose in plasma were measured at 21 weeks. RESULTS: Diets unbalanced for total protein, readily available carbohydrate, Mo or cod liver oil each increased the worm counts after 6 weeks of secondary infection (at 25 weeks of age) and FEC during secondary infection. Low intake of a highnutrient diet restricted liveweight gain but did not affect the development of resistance, as indicated by worm counts and FEC. Defi ciency of available carbohydrate resulted in reduced liveweight gain and reduced concentration of glucose in plasma. There was a reduction in jejunal mast-cell protease concentration in sheep fed unbalanced rations. CONCLUSIONS: The parasitology results and reduction in the concentration of jejunal mast-cell protease observed in sheep fed unbalanced rations suggest that the nutrient defi ciencies and the fi sh-oil supplement may have acted via inhibition or retardation of the host's acquired immune response. Diets unbalanced for a range of components adversely affected the acquired protective response to T. colubriformis to a similar extent and appeared to involve a similar mechanism as each other. The quality of the diet was more important than quantity for the development of resistance, and soluble carbohydrate was an essential component.

Control of horn flies (Haematobia irritans) and gastrointestinal parasites and its relation with cow–calf performance

The objective of this study was to assess the effects of horn fly and gastrointestinal (GI) nematode control on cow–calf performance with a spring-calving system. A total of 508 cow–calf records from two locations in Louisiana were available for study over two trials (2005 and 2006). Cow and calf pairs were stratified by cow age, calf sex, calf age, calf sire breed and calf sire and randomly assigned to three replicate treatment groups across the two locations. The treatments were: (1) no horn fly or GI nematode control; (2) horn fly control administrated to cows with insecticidal ear tags applied in late-May (start of trial); (3) GI nematode control administrated to calves in late-May, mid-July and late-August (each calf received fenbendazole at the rate of 5mgkg−1 body weight); and (4) horn fly and GI nematode control as stated above. Length of the trials ranged from 115 to 124 days (late-May to weaning in late-September or early-October). Cows and calves were weighed at the start of the trial, mid-July and weaning. Weekly horn fly counts were conducted. Individual calf fecal samples were collected in late-May, mid-July, late-August, weaning and 10–14 days after late-May and late-August collections. Cows treated for horn flies had lower (P<0.05) fly counts compared with untreated cows for each trial; however, overall fly counts for the treated cows at one location exceeded over 70 flies per side. Calves treated with fenbendazole had lower (P<0.01) GI nematode fecal egg counts (FEC) for the 10–14 day post-treatment collections. Calves treated GI nematodes and whose dams were treated for horn flies had numerically higher or greater (P<0.05) total calf gains (8.6kg and 11.8kg) in both trials than untreated calves. Weight gain differences for fenbendazole-treated calves compared with untreated calves were of greater magnitude from mid-July to weaning than weight gain differences from late-May to mid-July in both trials. There were no treatment differences for any of the cow response traits. In conclusion, improvement in calf growth from both horn fly and GI nematode treatments were realized even with marginal levels of fly control and a greater response in calf growth resulted when deworming of spring-born calves occurred when they were 4 months of age or older.

Effectiveness evaluation of several cattle anthelmintics via the fecal egg count reduction test

Utilizing groups of cograzed, naturally infected beef-type heifers, three fecal egg count reduction tests were conducted in the later months of 2007 at the University of Arkansas. Each test was 28 days in length consisting of individual animal fecal nematode egg counts and coprocultures. Both original and generic ivermectin injectable formulations were used in two of the tests at 0.2 mg/kg BW, with FECR percentages never exceeding 90% in either test. Oral fenbendazole was evaluated at 5 and 10 mg/kg BW, with FECR%'s exceeding 90% on all occasions, but with a precipitous drop when recently treated animals were treated at the lower dose. Evaluated in one test, injectable moxidectin given at 0.2 mg/kg BW resulted in egg count reductions of 96-92% (days 7 to 28). Also evaluated in one test, albendazole delivered orally at 10 mg/kg BW was 98% and 97% effective at 17 and 28 days post-treatment. For all tests, coprocultures conducted post-treatment contained only Cooperia spp. larvae (benzimidazole use), relatively unmodified percentages of Cooperia spp. and Haemonchus spp. larvae (ivermectin use), and primarily Cooperia spp. larvae with a small percentage of Haemonchus spp. larvae (moxidectin use).

A large-scale clinical field study to evaluate the efficacy and safety of an oral formulation of the amino-acetonitrile derivative (AAD), monepantel, in sheep in New Zealand

AIM: To evaluate the efficacy and safety of an oral formulation of the novel anthelmintic, monepantel (AAD 1566), in sheep, in comparison with some other anthelmintics currently registered in New Zealand. METHODS: A study was conducted on 18 farms located throughout the North and South Islands of New Zealand. On each farm, sheep naturally infected with the target nematodes were randomly assigned to groups, which were then treated with either monepantel, at a minimum dose rate of 2.5 mg/kg, or one of five other anthelmintics encompassing the range of single-entity and combination formulations that are commercially available in New Zealand, or left untreated as controls. Faecal samples were collected from all sheep pre-treatment (1–3 weeks before treatment), at the time of treatment, and approximately 1, 2 and 3 weeks after treatment (Days 7, 14 and 21). Faecal nematode egg counts (FEC) were measured in all samples, and the efficacy of treatments, as indicated by reductions in FEC, calculated. All sheep were inspected at least daily, to check for any adverse effects of treatment. RESULTS: On all 18 farms, on Days 7, 14 and 21 (54 test points), the efficacy of the monepantel solution was >95%. At Days 7 and 14 post-treatment, efficacies >99% were recorded in 15 flocks. At Day 21 post-treatment, efficacies >98% were recorded in 13 flocks. Monepantel was as effective, or more effective, than the registered anthelmintics with which it was compared. Moreover, it was effective against strains of nematodes resistant to one or more of the currently available broadspectrum anthelmintics. The monepantel solution used in this study was well tolerated by the sheep, and no adverse events could be attributed to its use. CONCLUSIONS AND CLINICAL RELEVANCE: When administered as an oral formulation under field conditions, at a minimum dose rate of 2.5 mg/kg, monepantel appeared to be highly effective against all the major genera of gastrointestinal nematodes of sheep, including Haemonchus, Teladorsagia (=Ostertagia), Trichostrongylus, Cooperia, Nematodirus, Chabertia and Oesophagostomum. This included strains resistant to the currently available broad-spectrum anthelmintics. Monepantel is the first compound from the recently discovered amino-acetonitrile derivative (AAD) class of anthelmintics to be developed for use in sheep.

An evaluation of anthelmintic properties, assessed using faecal nematode egg counts, of New Zealand native flax (Phormium tenax)

AIM: To investigate the anthelmintic properties of New Zealand native flax (Phormium tenax) for cattle, using a faecal egg count reduction test (FECRT). METHODS: Twenty-six heifer calves with high (>300 epg) faecal nematode egg counts (FEC) were paired into two groups and fed either chopped flax leaves ad libitum, or barley straw at an equivalent dry matter (DM) rate, from Day 0–7; all were supplemented with 1.5 kg/head/day cereal feed supplement. On Days 8–10, all heifers were fed a common diet of 3.5 kg DM/ head/day barley straw and 1.5 kg/head/day cereal feed supplement. Heifers were weighed and faecal samples were collected on Days —6, 0, 7, and 10; samples were analysed in triplicate for FEC. The nutritive value of the flax and straw was analysed. RESULTS: Both the flax and straw had low dry matter digestibility (DMD) and protein content. Although the flax-fed claves grew more than the controls, this may have been related to gut fill. Total daily faecal egg output was similar for flax and straw groups on Day 7 (14.7 vs 15.0 x 106 eggs/day, respectively) and Day 10 (14.9 vs 15.1 x 106 eggs/day, respectively). There was no difference in the change in FEC with time between the calves fed flax or straw diets. CONCLUSION: Consumption of flax leaves did not reduce FEC in calves with a mixed nematode infection.

Grazing willow ( Salix spp.) fodder blocks for increased reproductive rates and internal parasite control in mated hoggets

A grazing experiment, conducted for 116 days from 19 January to 15 May in the late summer/autumn of 2006 at Massey University's Riverside dry-land Farm, near Masterton (New Zealand), compared effects of grazing willow ( Salix spp.) fodder blocks or perennial ryegrass ( Lolium perenne)/white clover ( Trifolium repens) pasture, during the pre-mating and mating periods, on gastrointestinal nematode parasite control and reproductive rates in 7-month old ewe hoggets. A rotational grazing system with 348 weaned Romney ewe hoggets was used, with 116 hoggets per treatment (control pasture with regular anthelmintic drenching, control pasture with trigger drenching and willow fodder blocks with trigger drenching). Hogget live weights (LW), dag scores (DS), faecal nematode egg counts (FEC) and reproductive rates at foetal ultrasound scanning, lambing, tail docking and weaning were measured. Total N concentration (35 g/kg dry matter; DM), organic matter digestibility (OMD; 0.68) and metabolisable energy (ME; 10 MJ/kg DM) were similar for fodder block pasture and control pasture; the selected tree fodder had lower concentrations of N (24 g/kg DM) and was higher in OMD (0.74) and ME (10.4 MJ/kg DM). Tree fodder contained higher concentrations of condensed tannins (CT; 22.9 g/kg versus 1.6 g/kg DM) than control pasture and herbage in willow fodder blocks. Grazing willow fodder blocks increased LW gain (approximately 97 g/day versus 86 g/day) and increased reproductive rate corrected to equal LW by approximately 17 lambs/100 hoggets mated, due to increases in both oestrus activity and conception rates (hoggets pregnant/100 mated). Calculated daily DM (1.41 kg) and ME (14 MJ) intakes were similar in all groups. Calculated daily CT intake (6.0 g versus 2.1 g) and CT intake/100 g CP intake (2.2 g versus 0.7 g) were higher for willow fodder block hoggets than for the control pasture groups, and this may have increased the flow of undegraded dietary protein to the small intestine leading to increases in reproductive rates of this group. Grazing willow fodder blocks failed to reduce the number of anthelmintic drenches (3) needed to maintain FEC below 1000 eggs/g wet faeces, but was successful in reducing DS compared to grazing conventional ryegrass/white clover pastures. Grazing willow fodder blocks can be beneficial in sustainable farming systems since tree fodder can sustain growth rates, increase reproductive rates and reduce dag formation in parasitized hoggets.

Brave or gullible: Testing the concept that leaving susceptible parasites in refugia will slow the development of anthelmintic resistance

AIM: To test the theory that creating a reservoir of unselected worms by leaving a proportion of lambs in a flock untreated with anthelmintic, i.e. in refugia, will slow the development of anthelmintic resistance in nematode parasite populations. METHODS: Newly weaned Romney lambs (n=180) were infected with two nematode parasite species, Teladorsagia (=Ostertagia) circumcincta and Trichostrongylus colubriformis. For each species, the challenge doses contained a mixture of infective larvae from benzimidazole-resistant and -susceptible isolates calculated to yield, from the combined population, a 95% reduction in faecal nematode egg counts (FEC) following treatment with albendazole. Once the infections were patent, the lambs were divided into nine groups of 20 animals, and each group was allocated to one of three treatments. In Treatments 1, 2 and3, 100%, 90% and 80% of animals were treated with an anthelmintic, respectively. For treatments 2 and 3, the heaviest animals remained untreated. Following treatment, each group was moved to its own previously prepared low-contamination pasture. Lambs grazed this pasture for 7 weeks before again being treated and moved to new low-contamination pastures (Shift 1 and Shift 2). The parasite populations on pasture resulting from the different treatments were subsequently sampled using tracer lambs, and worm eggs derived from these were used in both egg-hatch assays (EHA) and larval development assays (LDA), to measure albendazole-resistance status. RESULTS: Treating all animals each time the groups were moved to new low-contamination pastures resulted in higher levels of albendazole resistance (p<0.05), measured using EHA and LDA, in subsequent parasite generations than when either 10 or 20% of animals were left untreated. However, higher FEC in the tracer lambs grazed on pastures in Treatments 2 and 3, compared with Treatment 1, indicated an increased level of pasture contamination as a result of leaving some animals untreated. CONCLUSIONS: The results demonstrate that creating a reservoir of unselected parasites slows the development of anthelmintic resistance, and emphasises the risk of treating all animals prior to a shift on to low-contamination pasture. However, higher levels of pasture contamination, resulting from untreated animals, indicate the difficulty in managing both worm control and resistance.

Managing anthelmintic resistance: Untreated adult ewes as a source of unselected parasites, and their role in reducing parasite populations

AIMS: To test the hypotheses that when untreated adult ewes are rotationally grazed (follow behind) on pastures after lambs receiving routine anthelmintic treatments, the ewes can function as a source of unselected parasites in refugia, capable of slowing the development of anthelmintic resistance, and suppress the build-up of parasites resulting from the development of anthelmintic resistance. METHODS: Firstly, the potential of untreated adult ewes to slow the development of anthelmintic resistance, and to suppress parasite populations under differing levels of anthelmintic efficacy, was investigated using a simulation model. Secondly, a field trial with three replicates of each treatment compared two grazing systems (lambs only vs lambs followed by ewes) and two types of anthelmintic, viz albendazole (ALB), to which resistance was present (faecal nematode egg count reduction (FECR)=57–59%) and ivermectin plus levamisole (IL), to which resistance was absent (FECR=97–99%), in a factorial treatment structure. Parasite populations were monitored using faecal nematode egg counts (FEC), faecal larval cultures, pasture larval sampling, and slaughter of tracer lambs. Animal performance was measured using liveweight, dag score, body condition score, and fleece weights. RESULTS: Model simulations indicated that parasites cycling in the untreated ewes could slow the development of resistance being selected for by the anthelmintic treatments given to lambs and this could occur without a nett increase in larval numbers on pasture. Further, as worm control in the lambs declined with increasing levels of anthelmintic resistance the ewes increasingly functioned as nett removers of parasite larvae, effectively reducing parasite population size. In the field trial, untreated adult ewes contributed to pasture infestations of most parasite species, but not Nematodirus spp. Parasite species on pasture and infecting lambs changed when ewes were present, but larval populations on pasture in the autumn were no greater than when lambs grazed alone. In the presence of anthelmintic resistance, parasite populations were reduced when ewes grazed in rotation with lambs, implicating the ewes as nett removers of parasite challenge. CONCLUSIONS: Untreated adult ewes were a source of unselected genotypes, capable of slowing the development of anthelmintic resistance in most, but not all, parasite species. Further, the potential of adult ewes to remove from pasture more parasite larvae than they contribute through faecal contamination indicates a potentially useful role in suppressing parasite populations, particularly when worm control in lambs is less effective as a result of anthelmintic resistance.

Inheritance of faecal nematode egg count in Barbari goats following natural Haemonchus contortus infection

Genetic parameters for faecal nematode egg count were estimated in naturally infected Barbari goats maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 5 years (1999 through 2003). Faecal egg count (FEC) data on 891 records of Barbari goats descended from 69 bucks and 241 does were used in this study. Analyses were carried out by restricted maximum likelihood (REML), fitting an animal model and ignoring or including maternal genetic or permanent environmental effects. Three different animal models were fitted. Direct heritability estimates were inflated substantially for this trait when maternal effects were ignored. The direct heritability estimates for the trait ranged from 0.05 to 0.13 depending on the model used. Low (0.04) maternal heritability estimate was observed for this trait in our study. Moderate estimate of the fraction of variance due to maternal permanent environmental effects ( c 2) for faecal egg count ( c 2 = 0.10) was also observed. Results suggest that direct and permanent environmental maternal effects were important for this trait, however, maternal additive effects had less impact on this trait.

Immunological responses and cytokine gene expression analysis to Cooperia punctata infections in resistant and susceptible Nelore cattle

Cellular and humoral immune response, as well as cytokine gene expression, was assessed in Nelore cattle with different degrees of resistance to Cooperia punctata natural infection. One hundred cattle (male, weaned, 11–12 months old), kept together on pasture, were evaluated. Faecal and blood samples were collected for parasitological and immunological assays. Based on nematode faecal egg counts (FEC) and worm burden, the seven most resistant and the eight most susceptible animals were selected. Tissue samples of the small intestine were collected for histological quantification of inflammatory cells and analysis of cytokine gene expression (IL-2, IL-4, IL-8, IL-12p35, IL-13, TNF-α, IFN-γ, MCP-1, MCP-2, and MUC-1) using real-time RT-PCR. Mucus samples were also collected for IgA levels determination. Serum IgG1 mean levels against C. punctata antigens were higher in the resistant group, but significant differences between groups were only observed 14 days after the beginning of the experiment against infective larvae (L3) and 14 and 84 days against adult antigens. The resistant group also presented higher IgA levels against C. punctata (L3 and adult) antigens with significant difference 14 days after the beginning of the trial ( P < 0.05). In the small-intestine mucosa, levels of IgA anti-L3 and anti-adult C. punctata were higher in the resistant group, compared with the susceptible group ( P < 0.05). Gene expression of both T H2 cytokines (IL-4 and IL-13) in the resistant group and T H1 cytokines (IL-2, IL-12p35, IFN-γ and MCP-1) in the susceptible group was up-regulated. Such results suggested that immune response to C. punctata was probably mediated by T H2 cytokines in the resistant group and by T H1 cytokines in the susceptible group.

An examination of the relative reliability of laboratory case submissions in determining the prevalence of anthelmintic resistance in sheep nematodes in New Zealand, and the possible influence of test analysis methodology on such data

AIM: To evaluate the likely reliability of laboratory case submissions in assessing the prevalence of anthelmintic resistance in sheep nematodes in New Zealand, and to examine the possible influence of two alternative faecal nematode egg count reduction (FECR) analysis methodologies on such data. METHODS: A comparison was made between the prevalence of anthelmintic resistance determined using faecal egg count reduction tests (FECRTs) conducted on randomly selected sheep farms in a national survey with those derived from similar case material submitted to a veterinary pathology laboratory on a more ad-hoc basis. A comparison was also made between two alternative FECR analysis methodologies using the latter data. One methodology involved a partially differentiated procedure in which FECRs for individual nematode genera were only undertaken in those instances where reductions in total strongylid faecal nematode egg counts (FECs) (excluding Nematodirus) of <95% were recorded. The other was a fully differentiated method where reductions in FECs for individual parasites were undertaken in all cases. RESULTS: Although there were some differences between them the results showed that there were considerable similarities between the prevalence data obtained from both the national survey and laboratory case submissions. This was particularly evident in relation to the overall pattern of involvement of the various nematode genera and the types of anthelmintic concerned. A comparison between laboratory case submission data analysed using a partially differentiated FECR methodology with that of a fully differentiated procedure, however, suggested that the use of the former practice was likely to lead to the ‘true’ prevalence of resistance being underestimated. CONCLUSIONS: The results of this study indicate that examination of FECRT case submissions to veterinary laboratories may offer a useful source of information regarding changes in the prevalence of anthelmintic-resistant sheep nematodes in New Zealand. They also lend support to suggestions that the recently completed national survey may have provided a conservative estimate of the prevalence of such resistance.

Multiple species of nematodes resistant to ivermectin and a benzimidazole-levamisole combination on a sheep farm in New Zealand

AIM: To confirm the presence of multiple anthelmintic resistance on a sheep farm in New Zealand. METHODS: Three groups of 10 weaned Romney-cross lambs were treated either with an oral dose of ivermectin (0.2 mg/kg), or a benzimidazole/levamisole (BZ/LEV) combination (4.75 albendazole and 7.5 mg/kg levamisole), or were left untreated. Ten days later, animals were necropsied, and adult worms recovered and identified from the abomasa and small intestines. Pre- and post-treatment faecal nematode egg counts (FEC) were recorded, and larval cultures were performed. RESULTS: In a faecal egg count reduction test (FECRT), adjusted to reflect pre- and post-treatment larval culture results, ivermectin resistance was detected in Teladorsagia (Ostertagia), Trichostrongylus and Haemonchus spp, while BZ/LEV combination-resistant Teladorsagia and Trichostrongylus spp were also present. Adult worm counts confirmed these results, and identified the species involved as Teladorsagia circumcincta, Trichostrongylus colubriformis and H. contortus. CONCLUSION: Multiple, multi-generic anthelmintic resistance was confirmed on a sheep property in New Zealand. This included the first confirmed case of ivermectin resistance in T. colubriformis from sheep in New Zealand.

Genetic analysis of faecal worm egg count in South African Merinos under natural challenge

Sheep from a Merino selection experiment at the Tygerhoek research farm in the Southern Cape provided material for this study. The selection lines involved included a line selected for clean fleece weight, a “Wet and Dry” line, a fine wool line and an unselected Control line. Rectal faeces samples were obtained from individual animals at 13 to 16 months of age, after drenching was withheld for at least 10 weeks. Nematode eggs in these samples were counted. Fitting the appropriate fixed effects, the heritability of untransformed, cube root transformed and log transformed faecal nematode egg count (FEC) was obtained from single-trait analyses. The effects of sex and birth year were involved in a significant interaction. Means for FEC were generally higher in ram progeny than in ewes, but the magnitude of the sex difference was not consistent. Multiple lambs had a slightly lower mean for FEC than singles, while FEC was unaffected by dam age. The heritability of FEC was estimated at between 0.14 for untransformed data and 0.18 for log transformed FEC. Genetic correlations of log transformed FEC with two-tooth staple strength (-0.49) and coefficient of variation of fibre diameter (0.30) were favourable. Clean fleece weight was unfavourably related to FEC on a genetic level (0.19). Selection for resistance to parasitic nematodes after natural challenge should thus be feasible in the Merino lines studied. Keywords : Fleece weight; genetic correlation; heritability; live weight; resistance South African Journal of Animal Science Vol. 37 (4) 2007: pp.237-247

Willow ( Salix spp.) fodder blocks for growth and sustainable management of internal parasites in grazing lambs

A grazing experiment was conducted in the East Coast region of the North Island of New Zealand with 180 weaned ram lambs grazing typical dryland summer pasture versus grazing willow ( Salix spp.) fodder blocks. The experiment was conducted over a 14-week period with three forage treatments, comprising control pasture, restricted access to willow fodder blocks and full access to willow fodder blocks, with each treatment further divided into undrenched and regularly anthelmintic drenched groups. Live weight (LW) and dag score (DS) were recorded at 14-day intervals. Fifteen lambs in both drenched and undrenched groups were regularly monitored for faecal nematode egg counts (FEC) and nematode larval cultures (LC). Carcase weight (CW; kg) and LW (kg) data was collected from 12 additional lambs slaughtered at the beginning of the experiment to predict initial CW of the experimental lambs from their initial LW. At the end of the grazing experiment, all lambs were slaughtered in a commercial abattoir; CW and GR (fatness) was recorded. The abomasum and small and large intestines were collected from 10 lambs from each undrenched group for estimation of total worm nematode numbers. Organic matter digestibility (OMD; 0.65) and metabolisable energy (ME; 9.7 MJ/kg DM) content were similar for fodder block pasture and control pasture; the selected tree fodder had a higher OMD (0.71) and ME concentration (10.7 MJ/kg DM). Herbage condensed tannin (CT) concentration in willow fodder blocks was consistently higher than the trace CT levels detected in control pasture (14.5 g/kg DM versus 6.2 g/kg DM); tree fodder contained higher concentrations of CT (45.5 g/kg DM). Undrenched lambs grazing either control pasture or willow fodder blocks had lower LW gain (LWG) and CW gain (CWG) than lambs regularly drenched with anthelmintic (P<0.0001). Lambs grazing fodder blocks had consistently lower DS and carcase GR and undrenched lambs grazing fodder blocks had reduced worm burdens of economically important internal parasites compared with undrenched lambs grazing control pasture. Lamb growth rates were reduced by restricted access to willow fodder blocks (P<0.01), but not by full access. Undrenched lambs grazing fodder blocks with full access had similar LWG, final DS and carcase GR to regularly drenched lambs grazing control pasture (the conventional farming system), but had reduced rates of CWG. It was concluded that willow fodder blocks could have a place in integrated systems for the control of internal parasites in grazing lambs, leading to a reduction in anthelmintic drench use, but that this would probably result in lower CW relative to regularly drenched lambs.