Gastrointestinal Nematode Parasites Research Articles

Molecular cloning and characterisation of ovine dual oxidase 2

The dual oxidases (DUOX1 and DUOX2) are NADPH-dependant hydrogen peroxide-producing enzymes that are reported to function in a physiological capacity and as a component of the mucosal immune response. We have previously reported increased expression of the DUOX2 gene in the gut mucosa of sheep in response to gastrointestinal nematode (GIN) challenge. In this paper, we report the cloning of the full-length ovine DUOX2 transcript, using a PCR based strategy. The ovine DUOX2 transcript includes an ORF of 4644 bases, and encodes a protein with 97% identity to the bovine sequence. We also cloned a fragment of DUOX1 (encompassing nucleotides 2692–2829), and the proximal promoter sequence of DUOX2. Through analysis of sequence data we have confirmed that DUOX1 and DUOX2 are co-located in a head to tail arrangement conserved across many species. Alignment of the sequences to the ovine genome predicts a location of this gene cluster on ovine chromosome 7. We quantified the expression of ovine DUOX1 and DUOX2 transcripts in 24 different sheep tissues, and discovered tissue specific expression signatures. DUOX2 was found to be most highly expressed in tissues of the gastrointestinal tract, while expression of DUOX1 predominated in the bladder. Rapid amplification of cDNA ends (RACE) analysis identified the existence of multiple 5′ UTR variants in DUOX2, ranging in size from 32 to 242 nucleotides, with 3 distinct transcribed regions. Real time PCR quantification of the DUOX2 UTR variants revealed that these were differentially expressed between tissues, and at various stages of the response to GIN parasite infection. The collective evidence suggested a complex regulation of DUOX2, prompting a bioinformatic analysis of the proximal promoter regions of ovine DUOX2 to identify potential transcription factor binding sites (TFBS) that may explain the differences in the observed expression of the transcript variants of DUOX2. Possible transcription factor families that may regulate this process were identified as Kruppel-like factors (KLF), ETS-factors, erythroid growth receptor factors (EGRF) and myogenic differentiation factors (MYOD).

Recirculating elutriator for extracting gastrointestinal nematode larvae from pasture herbage samples

Gastrointestinal nematode (GIN) parasites present an important limitation to ruminant production worldwide. Methods for quantifying infective larvae of GIN on pastures are generally tedious, time-consuming, and require bulky equipment set-ups. This limitation to expedient data collection is a bottleneck in development of pasture management practices that might reduce pasture infectivity. We modified a soil elutriator concept for extracting GIN larvae from fresh herbage samples. Elutriators were constructed from readily available parts and compared to the Baermann funnel sedimentation method for larvae extraction. More samples could be extracted per day in the elutriator than in a Baermann unit with extraction times of 8min versus 24h, respectively. Accuracy, measured as maximum recovery of larvae seeded onto herbage samples, did not differ between extraction methods (62.3 vs. 69.8% for elutriator and Baermann, respectively, P>0.05). Larvae recovery from herbage in elutriators showed a strong loge relationship with extraction time (r2>0.98), which will allow development of accurate correction factors for specific herbages to predict total larvae densities at extraction times less than those needed for maximum recovery. An extraction time of 8min per sample gave the best compromise of speed, accuracy, and precision as measured by regression confidence bands and root mean square error of analysis of variance. Precision of the elutriator extraction for pasture samples was comparable to published methods and was not affected by forage species or canopy strata. The elutriator method was sensitive enough to detect differences in larvae density as small as 8larvaeg−1 DM among pasture treatments. Elutriators extracted nematode larvae from herbage samples with accuracy and precision similar to existing methods, but did it much faster. Elutriation shows promise as a rapid method for extracting infective GIN larvae from pasture herbage.

Evaluation of anaemia in Nigerian goats using FAMACHA© eye colour chart: a preliminary study

A preliminary study was carried out on the possibility of using the FAMACHA eye colour chart to predict the level of anaemia in 280 Nigerian goats of varied ages slaughtered at the Nsukka abattoir, in Enugu State, Nigeria. Three indices of anaemia, namely packed cell volume (PCV), red blood cell (RBC) counts and haemoglobin (Hb) concentrations were compared with the colour of the ocular membranes of the goats. The colours of the ocular conjunctiva of all animals were scored on a 1–5 scale using the FAMACHA© card, and blood samples were collected from each animal for determination of PCV, RBC counts and Hb concentration. Correlations between eye colour scores and the duo of PCV and Hb concentrations were highly significant and negative. Haemonchus contortus was the most predominant gastrointestinal nematode parasite observed in the study with average larval recovery of 70.18 %. Age has no effect on the predictability of anaemia by the FAMACHA© technique. It was concluded that the FAMACHA method can be used by farmers in Nigeria to identify anaemic goats particularly in conditions of haemonchosis which is one of the main causes of anaemia in goats and the most predominant gastrointestinal nematode in small ruminants in the study area. It is, therefore, believed that these preliminary findings will form a basis for further work on validating the use of FAMACHA© in Nigerian goats.

Exposure to pasture borne nematodes affects individual milk yield in Swedish dairy herds

The association between exposure to gastrointestinal nematode (GIN) parasitism, indicated by elevated individual optical density ratio (ODR) to Ostertagia ostertagi, and individual milk production was analysed in dairy cows. The multivariable analysis also accounted for other sources of variation than exposure to GIN parasitism. Intra- and inter-herd variation in parasite exposure was also evaluated. Organic and conventional herds located in south-east Sweden (13 herds per system) were visited during the housing period 2009–2010. Levels of all major pasture-borne helminths in Sweden (O. ostertagi, Fasciola hepatica and Dictyocaulus viviparus) were determined in bulk tank milk, cow milk and serum (only for O. ostertagi). Their specific antibodies were detected using three different ELISAs (Svanova Biotech) and the optical density of the sample was expressed as ODR. Positive cases of Dictyocaulus and Fasciola were seldom found. Variation in ODR in serum samples for Ostertagia was higher within herds than between herds. Correlations between ODR for Ostertagia in serum and milk parameters were significant and negative. In the multivariable analysis, two models were performed separating data from primiparous and multiparous cows. Results from mixed models showed that daily milk yield was significantly influenced by Ostertagia ODR for multiparous cows. No interactions were found between Ostertagia ODR values and herd type.

Genetic and environmental influences on faecal nematode egg counts of Jamunapari goats in India

The present study was carried out from 1999 to 2003 to determine the genetic and environmental influences of faecal egg count (FEC), an indicator of host resistance, in adult Jamunapari...

Possibilities to breed for resistance to nematode parasite infections in small ruminants in tropical production systems

Gastrointestinal nematode parasitism is the most important disease affecting livestock production systems in developing countries, particularly small ruminant production systems. Of particular importance are infections with the strongyle Haemonchus contortus. Integrated disease control strategies are required, including improved management, nutrition and wise use of anthelmintic chemicals. Increasingly, selection of sheep or goats for improved nematode resistance is viewed as a valuable option to complement other control measures. Breeding for resistance is possible because of the existence of extensive genetic variation in resistance, both within and between breeds of sheep and goats. Such breeding schemes are most likely to be based on choice of appropriate breeds adapted to the local environmental conditions, followed by phenotypic selection for resistance. Goal and selection objective traits are likely to include performance (e.g. growth rate) under conditions of parasite challenge, faecal egg count (FEC) and measures of anaemia. With current technologies, genetic markers are likely to be too expensive and logistically difficult to incorporate into breeding schemes in tropical or developing countries. Genotype by environment interactions may be expected, particularly when comparing animals in environments that differ in the extent of parasite challenge or differ in the quality of available nutrition. However, there is no reason to expect antagonistic genetic relationships between performance and resistance, and selection indices should be readily constructed that improve both performance and resistance. If FEC is decreased, then pasture contamination should also decrease, leading to additional benefits for all sheep grazing the same pasture. Finally, breeding for nematode resistance should lead to lasting and sustained improvements in resistance or tolerance. There is no empirical evidence to suggest that nematodes will evolve rapidly in response to resistant hosts, and mathematical models based on genetic and biological principles also suggest that resistance should be sustainable.

Gastrointestinal nematodes and body condition scores of goats slaughtered in Nsukka, Nigeria.

Gastrointestinal (GI) nematodes of 210 trade goats slaughtered in Nsukka area of Enugu state and their effects on body conditions was studied between May and August, 2011. The body condition of each goat were determined and scored on a scale of 1 – 5. Faecal samples were then collected from the goats before slaughter and their respective GI tract washings after slaughter for parasitological examination using standard procedures. The results revealed that Strongyles were the most prevalent nematode encountered in the goats (90.0%). The prevalence of mixed infection were 40.95%, 12.87%, 9.52% and 11.09% respectively for Strongyle + Strongyloides, Strongyle + Trichuris, Strongyloides + Trichuris and Strongyle + Strongyloides + Trichuris. Haemonchus contortus was the predominant nematode infecting the goats followed by Trichostrongylus spp, Oesophagostomum spp and Strongyloides spp in that order. Sex and age of the animals were shown to have association with prevalence but significant (p> 0.05) difference was not found. There was an inverse and significant (p ? 0.05) relationship between body condition scores and the duo of mean egg per gram of faeces and adult worm burden of the goats. We concluded that GI nematode parasites are major problems of the goats slaughtered in Nsukka abattoir and the parasites had a remarkable effect on the body condition scores of the goats. KEY WORDS : Gastrointestinal nematode; prevalence; goats; body condition score; Nigeria

Relationship between susceptibility of Blackface sheep to Teladorsagia circumcincta infection and an inflammatory mucosal T cell response

Teladorsagia circumcincta is the most economically important gastrointestinal (abomasal) nematode parasite of sheep in cool temperate regions, to which sheep show genetically-varying resistance to infection. Lambs, from parents with genetic variation for resistance, were trickle infected with L3 larvae over 12 weeks. 45 lambs were identified with a range of susceptibilities as assessed by: adult worm count at post mortem, faecal egg count (FEC) and IgA antibody levels. This project investigated the correlation of T cell cytokine expression and resistance to infection at the mature stage of response, when the resistant lambs had excluded all parasites.Histopathology showed only minor changes in resistant animals with a low level lymphocyte infiltration; but in susceptible lambs, major pathological changes were associated with extensive infiltration of lymphocytes, eosinophils and neutrophils.Absolute quantitative RT-qPCR assays on the abomasal lymph node (ALN) revealed a significant positive correlation between IL6, IL21 and IL23A transcript levels with adult worm count and FEC. IL23A was also negatively correlated with IgA antibody levels. Significantly positive correlation of TGFB1 levels with adult worm count and FEC were also seen in the abomasal mucosa. These data are consistent with the hypothesis that the inability to control L3 larval colonization, adult worm infection and egg production is due to the activation of the inflammatory Th17 T cell subset.

Research and implementation of novel approaches for the control of nematode parasites in Latin America and the Caribbean: Is there sufficient incentive for a greater extension effort?

The widespread presence of anthelmintic resistant gastrointestinal parasitic nematodes in outdoor ruminant production systems has driven the need to identify and develop novel approaches for the control of helminths with the intention to reduce the dependence on commercial anthelmintic drugs. This paper identifies what has been done in Latin America (LA) in terms of estimating the prevalence of anthelmintic resistance (AR) in ruminant production systems and the application of different novel approaches for the control of helminths in those systems, including research and extension activities. Firstly, the paucity of knowledge of AR is discussed in the context of different countries, as well as, the available economic resources for research, the technical infrastructure available and the practical difficulties of the production systems. It is then proposed that the search for novel approaches is not only driven by AR but also by the need for techniques that are feasible for application by resource-poor farmers in non-commercial subsistence farming systems. However, the commercial benefits of these approaches are often limited and so are funding inputs in most countries. The workers participating in the research into different novel approaches are identified as well as the different methods being studied in the different areas of LA according to their published results. In addition, the difficulties experienced during extension efforts to reach farmers and help them to adopt novel approaches for the control of parasitic nematodes in LA are discussed. The role of regulatory authorities in these countries is discussed as some methods of control might need an official confirmation of their efficacy as well as authorization prior to application as they may affect animal products (i.e. residues) and/or impose a hazard for animal welfare. The role of the pharmaceutical companies is also discussed.

Interactions between gastrointestinal nematode parasites and diarrhoea in sheep: Pathogenesis and control

Diarrhoea is a major impediment to profitable sheep production in many countries as it predisposes animals to blowfly strike and contaminates wool and meat carcasses. While it is accepted that nematode parasites are a major cause of diarrhoea in grazing animals, less is known about what facets of the host-parasite relationship lead to diarrhoea and what the most appropriate control strategies are. In this review, the relationship between gastrointestinal nematode infection and diarrhoea is discussed and it is concluded that in many cases, particularly in immunologically mature sheep, diarrhoea is not due to parasite infection per se but rather due to immunopathological processes. Mechanisms that lead to faecal softening in immune sheep are considered, and the question addressed as to whether anthelmintic treatment and selective breeding of naturally parasite-resistant sheep will effectively reduce the occurrence of diarrhoea.

Protective immunity against the gastrointestinal nematode Nippostrongylus brasiliensis requires a broad T-cell receptor repertoire

The parasitic gastrointestinal nematode Nippostrongylus brasiliensis induces massive expansion of T helper type 2 (Th2) cells in the lung and small intestine. Th2 cells are a major source of interleukin-4 and interleukin-13, two cytokines that appear essential for rapid worm expulsion. It is unclear whether all Th2 cells induced during infection are pathogen-specific because Th2 cells might also be induced by parasite-derived superantigens or cytokine-mediated bystander activation. Bystander Th2 polarization could explain the largely unspecific B-cell response during primary infection. Furthermore, it is not known whether protective immunity depends on a polyclonal repertoire of T-cell receptor (TCR) specificities. To address these unresolved issues, we performed adoptive transfer experiments and analysed the TCR-Vβ repertoire before and after infection of mice with the helminth N.brasiliensis. The results demonstrate that all Th2 cells were generated by antigen-specific rather than superantigen-driven or cytokine-driven activation. Furthermore, we show that worm expulsion was impaired in mice with a limited repertoire of TCR specificities, indicating that a polyclonal T-cell response is required for protective immunity.

Anticholinesterasic, Nematostatic and Anthelmintic Activities of Pyridinic and Pyrazinic Compounds

In the search for acetylcholinesterase inhibitors as a potential target for the discovery of anthelmintic drugs, a series of 27 pyridinic and pyrazinic compounds have been designed on the basis of molecular hybridization of two known AChE inhibitors, namely, tacrine and (-)-3-O-acetylspectaline, and on the concept of isosterism. The synthesized compounds generally presented moderate anticholinesterasic activities when compared with the positive control physostigmine, but one compound (ethyl 2-[(6-chloropyrazin-2-yl)sulfanyl] acetate) exhibited an in vitro ability to immobilize the root-knot nematode Meloidogyne incognita that was highly comparable to that of the positive control Temik. Moreover, in anthelmintic assays against the gastrointestinal parasitic nematode Nippostrongylus brasiliensis (L4), some of the compounds, such as (6-chloropyrazin-2-yl)sulfanyl ethanol (32, EC₅₀ = 33 nM), presented activities that were considerably stronger than that of the positive control albendazole (EC₅₀ = 340 nM). In the light of the positive results obtained in the anthelmintic evaluations, the acute oral toxicity of the representative compound diethyl 2,2'-[(3-nitropyridine-2,6-diyl) bissulfanediyl] diacetate was determined in rats, and the drug was shown to be non-toxic at a dose of 2000 mg/kg. These results, allied with the relatively simple structures of the active compounds and their facile synthesis, highlight their potential use as anthelmintic or nematicidic agents.

Biological control of Ascaris suum eggs by Pochonia chlamydosporia fungus

Ascaris suum is a gastrointestinal nematode parasite of swines. The aim of this study was to observe Pochonia chlamydosporia fungus on biological control of A. suum eggs after fungus passage through swines gastrointestinal tract. Eighteen pigs, previously dewormed, were randomly divided into three groups: group 1, treated with the fungus isolate VC4; group 2, treated with the fungus isolate VC1 and group 3 did not receive fungus (control). In the treated groups, each animal received a 9 g single dose of mycelium mass containing P. chlamydosporia (VC1 or VC4). Thereafter, animal fecal samples were collected at the following intervals: 8, 12, 24, 36, 48, 72 and 96 h after treatment beginning and these were poured in Petri dishes containing 2% water-agar culture medium. Then, 1,000 A. suum eggs were poured into each dish and kept in an incubator at 26 °C and in the dark for 30 days. After this period, approximately 100 eggs were removed from each Petri dish and morphologically analyzed under light microscopy following the ovicidal activity parameters. The higher percentage observed for isolated VC4 eggs destruction was 57.5% (36 h) after fungus administration and for isolate VC1 this percentage was 45.8% (24 h and 72 h) (p > 0.01). P. chlamydosporia remained viable after passing through the gastrointestinal tract of swines, maintaining its ability of destroying A. suum eggs.

Efficacy of fenbendazole, levamisole and ivermectin against gastrointestinal nematodes in Jamunapari goats

Efficacy of fenbendazole, levamisole and ivermectin was checked in comparison to untreated controls in twenty Jamunapari goats, naturally infected with gastrointestinal nematode parasites. Faecal examination at day 0 revealed an egg per gram of 930±175.1, 1350±421.1, 1060±224.9 and 800±279.7 in group A, B, C and D, respectively having five animals each. The results of larval culture examination revealed the presence of Haemonchus, Trichostrongylus, Oesophagostomum, Bunostomum and Strongyloides spp. in these animals. Faecal egg counts of the animals treated with fenbendazole (group A), levamisole (group B) and ivermectin (group C) were reduced by 23.66, 63.70 and 98.11%, respectively on day 14 post-treatment.

Efficacy of the cyclooctadepsipeptide PF1022A againstHeligmosomoides bakeri in vitroandin vivo

The cyclooctadepsipeptide PF1022A derived from the fungus, Mycelia sterilia, is characterized by a broad spectrum of activity against different parasitic gastrointestinal nematodes of livestock. In the present work the anthelmintic activity of PF1022A against Heligmosomoides bakeri, a widely used laboratory model was studied. Albendazole, ivermectin and levamisole served as reference. In vitro, PF1022A showed low activity on embryonation but significantly inhibited egg hatch (10 and 100 μg/ml), whereas albendazole (10 and 100 μg/ml) revealed statistically significant inhibitions of both embryonation and egg hatch. PF1022A (1-100 μg/ml) completely inhibited larval movement at most examination points. Comparable significant anthelmintic activity on the larval stages of H. bakeri was observed with levamisole (48-100%), while slightly lower activities were observed with ivermectin (20-92%) and albendazole (0-87%) at 1-100 μg/ml. PF1022A and levamisole significantly inhibited motility and egg release of adult worms, while albendazole and ivermectin failed to demonstrate activity. Significant worm burden reductions were achieved with PF1022A, levamisole and ivermectin in vivo. For example, at 0·125 mg/kg PF1022A a worm burden reduction of 91·8% was observed. The use of drug combinations did not further enhance the in vitro and in vivo activity of PF1022A. In conclusion, further investigations are warranted with PF1022A, as the drug is characterized by significant larvicidal and nematocidal activity in vitro and in vivo.

Predatory activity of the fungus Duddingtonia flagrans in equine strongyle infective larvae on natural pasture in the Southern Region of Brazil

Biological control is an alternative method to reduce the population of parasites through natural predators. A promising option of biological control in the reduction of infective larvae on pasture is the use of nematophagous fungi. In this study, the efficacy of the nematophagous fungus Duddingtonia flagrans in controlling gastrointestinal nematode parasites in field-raised horses was tested. Ten foals with an average age of 12 months were divided in two groups: five males constituted the treated group and five females constituted the control group. Each group was introduced in a field of mixed pasture with approximately 5 ha. The treated group received the fungus D. flagrans at a concentration of 10(6) chlamydospores per kilogramme of animal body weight daily, mixed with horse food for 5 months. The control group did not receive the fungus. Samples were collected to perform eggs per gramme (EPG) counts weekly. Coproculture and collection of pasture were done monthly for larvae counting. No significant difference was observed in the EPG counting and in the number of larvae recovered from coprocultures, where cyathostomines, Strongylus and Trichostrongylus spp. were found after monthly larvae counting. No significant difference was observed in the EPG counts, and Trichostrongylus sp. was identified. The number of recovered larvae on pasture was significantly lower in the treated group in the last month of treatment, showing a reduction of 73.5% (p < 0.05). As such, the fungus was able to reduce the number of infective larvae in the pasture. Nevertheless, this did not reflect in a decrease of parasitic infection during the 5-month study period.

Anthelmintic and cytotoxic activities of extracts of Markhamia obtusifolia Sprague (Bignoniaceae)

The anthelmintic activity of Markhamia obtusifolia Sprague (Bignoniaceae) leaf extracts was evaluated against the ruminant gastrointestinal nematode parasite Trichostrongylus colubriformis (Nematoda: Strongylida) using the in vitro egg hatch test. Also, the cytotoxic activity of aqueous extracts of M. obtusifolia was evaluated in cell line cytotoxicity assays. The results indicated that the effective concentration (EC50) for the water extract of M. obtusifolia leaves (0.46mg/mL; Confidence Interval [CI] 0.3–0.5mg/mL) was significantly lower than the EC50 for the acetone extract of M. obtusifolia (0.8mg/mL; CI 0.7–1mg/mL). Aqueous extracts were twice as potent as the acetone extracts. The EC90 (0.2mg/mL; CI 0.1–0.02) for thiabendazole (positive control) was significantly lower than the EC90 for the water extract of M. obtusifolia (10.7mg/mL; CI 8.3–13.7mg/mL). In the cytotoxicity bioassay, the lethal concentration (LC50) for the aqueous extract of M. obtusifolia was 0.476mg/mL, which was relatively high (low toxicity) in comparison to the highly toxic berberine (LC50=9.80μg/mL). The current study showed that M. obtusifolia plant extracts possess anthelmintic activity and are relatively non-cytotoxic, thus providing support for their use in traditional veterinary practices.

Kinetics of capture and infection of infective larvae of trichostrongylides and free-living nematodes Panagrellus sp. by Duddingtonia flagrans

Duddingtonia flagrans, a nematode-trapping fungus, has been investigated as an agent for biological control against infective larvae of gastrointestinal nematode parasites of production animals. The initial process of nematode-trapping fungi infection is based on an interaction between the trap structure of the fungus and the surface of the nematode cuticle. This report investigates by light and scanning electron microscopy the kinetics of capture and infection during the interaction of D. flagrans with the infective larvae (L(3)) of trichostrongylides and the free-living nematode Panagrellus sp. D. flagrans was cultivated for 7 days in a Petri dish containing agar-water. L(3) and Panagrellus sp. were inoculated in the Petri dishes and the samples consisting of agar-L(3)-fungi and agar-Panagrellus sp.-fungi were collected after 10, 20, 30, 40, 50, 60, and 70 min and 3, 4, 5, 10, 15, 20, and 25 h of interaction. All samples were observed by light microscopy. The samples with 1, 5, 15, and 25 h of interaction were also analyzed by scanning electron microscopy. The interaction was monitored up to 25 h. An initial differentiation of predation structures was observed after 30 min of interaction. The presence of traps and of captured L(3) or Panagrellus sp. occurred after 70 min. The live captured nematodes were observed up to 3 h of interaction. However, after 4 h, all Panagrellus sp. were dead. It took 15 h of interaction for the fungus to invade the L(3), and the presence of hyphae inside the nematode near the region of penetration was evident. At this time, the hyphae had filled the whole body of Panagrellus sp. The complete occupation of the body of L(3) occurred at 20 h of interaction and with 25 h the nematode was completely damaged except for the cuticle. Although the double cuticle of L(3) slows the penetration of D. flagrans, it was possible to verify that the process of trap formation and capture occurs quickly when both nematodes were tested, suggesting that the organisms would eventually be killed once in contact with the fungi encouraging the use of the fungus as a biological control agent.

Tannin rich peanut skins lack anthelmintic properties

Gastrointestinal nematode (GIN) resistance to synthetic anthelmintics in small ruminants has led to the evaluation of feed sources containing naturally occurring bioactive secondary metabolites that lessen parasite activity. Plants rich in condensed tannins (CT) can have beneficial anthelmintic properties. Peanut (Arachis hypogea L.) skins (testa), an agricultural by-product, are a rich source of CT, have low fiber and high levels of oil and crude protein, and have been incorporated into feed products for the cattle industry. Anthelmintic activity of pellets formulated with peanut skins was compared to that of commercial alfalfa (Medicago sativa L.) pellets (control diet) fed to lambs in two separate experiments, one with initially low (220eggsg−1feces; 2008) and the other high (4260eggsg−1feces; 2009) burden of GIN. In both experiments lambs were maintained on bermudagrass (Cynodon dactyon (L.) Pers.) pastures except when pellets were fed (six lambs per treatment) at 2.3% BW every other day three times a week. Overall, average daily intake of CT as quebracho (Schinopsis sp.) equivalents of peanut skin pellets formulated with 5% molasses was 0.38% BW (low GIN lambs), and that of peanut skin pellets formulated with 48% alfalfa and 7% molasses was 0.53% BW (high GIN lambs). Regardless of the initial level of GIN burden and the formulation of the peanut skin pellets, average daily weight gain of all lambs was about 94±7.2g per day. Increases in fecal egg count and decreases in blood packed cell volumes that occurred during the trials were not significantly different (P>0.05) between lambs fed the control alfalfa pellets and lambs fed peanut skin containing pellets. In these trials, intake of peanut skin may have been insufficient to decrease GIN parasite activity, or perhaps the low prodelphinidin subunit composition of CT in peanut skin prevented a beneficial response.

The Influence of MHC and Immunoglobulins A and E on Host Resistance to Gastrointestinal Nematodes in Sheep

Gastrointestinal nematode parasites in farmed animals are of particular importance due to their effects on production. In Australia, it is estimated that the direct and indirect effects of parasite infestation cost the animal production industries hundreds of millions of dollars each year. The main factors considered by immunologists when studying gastrointestinal nematode infections are the effects the host's response has on the parasite, which immunological components are responsible for these effects, genetic factors involved in controlling immunological responses, and the interactions between these forming an interconnecting multilevel relationship. In this paper, we describe the roles of immunoglobulins, in particular IgA and IgE, and the major histocompatibility complex in resistance to gastrointestinal parasites in sheep. We also draw evidence from other animal models to support the involvement of these immune components. Finally, we examine how IgA and IgE exert their influence and how methods may be developed to manage susceptible animals.