Epidemiology of gastrointestinal nematode parasitism in Suffolk and Gulf Coast Native sheep with special emphasis on relative susceptibility to Haemonchus contortus infection

Variants of NLRP3 Protein in Haemonchus contortus Infected Sheep: Impact on Immune Cell Responsiveness to LPS In Vitro

Pathogen recognition is an essential component to achieve the desired outcome of host protection. Nod-like receptor pyrin containing domain 3 (NLRP3) is a cytoplasmic pattern recognition receptor (PRR) with a wide array of agonists, such as PAMPs, DAMPs, ATP, bacterial product and viral products. Stimulation of the NLRP3 inflammasome results in proteolytic activation of IL-1β and IL-18, cell pyroptosis and classically, the induction of proinflammatory responses. St. Croix (STC) sheep have resistance traits exhibiting the appropriate T-helper type 2 immune response ensuing protection during helminth parasitic infection whereas parasite-susceptible Suffolk (SUF) sheep have an impaired response resulting in parasite establishment and adverse symptoms. The objective of these experiments was to determine if NLRP3 protein in H. contortus-infected SUF sheep was defective using the classical activation pathway of NLRP3 inflammasome. Peripheral blood mononuclear cells (PBMCs) derived from H. contortus-infected STC and SUF sheep were isolated from whole blood and treated (MCC950 treatment for 2 h followed by LPS treatment for 3 h, 1400 W treatment for 2 h followed by LPS treatment for 3 h, LPS treatment for 3 h or culture media for 3 h). qPCR analysis of LPS-stimulated PBMC revealed an upregulation in inflammatory associated genes IL-1β, TLR4, TNFα and NFκB (p < 0.0001) in STC PBMC and downregulation in IFNγ, IL-6 and iNOS for SUF PBMC. Pharmacological inhibition of iNOS in SUF PBMC resulted in an upregulation in the expression of IFNγ. These preliminary data begin to discover a relationship between NLRP3 activation and TLR4 signalling in PBMC of STC and SUF sheep.

Characterization of the Hepatic Transcriptome for Divergent Immune-Responding Sheep Following Natural Exposure to Gastrointestinal Nematodes

Infections with gastrointestinal nematodes (GINs) reduce the economic efficiency of sheep operations and compromise animal welfare. Understanding the host's response to GIN infection can help producers identify animals that are naturally resistant to infection. The objective of this study was to characterize the hepatic transcriptome of sheep that had been naturally exposed to GIN parasites. The hepatic transcriptome was studied using RNA-Sequencing technology in animals characterized as high (n = 5) or medium (n = 6) based on their innate immune acute-phase (AP) response phenotype compared with uninfected controls (n = 4), and with biased antibody-mediated (AbMR, n = 5) or cell-mediated (CMR, n = 5) adaptive immune responsiveness compared to uninfected controls (n = 3). Following the assessment of sheep selected for innate responses, 0, 136, and 167 genes were differentially expressed (DE) between high- and medium-responding animals, high-responding and uninfected control animals, and medium-responding and uninfected control animals, respectively (false discovery rate (FDR) < 0.05, and fold change |FC| > 2). When adaptive immune responses were assessed, 0, 53, and 57 genes were DE between antibody- and cell-biased animals, antibody-biased and uninfected control animals, and cell-biased and uninfected control animals, respectively (FDR < 0.05, |FC| > 2). Functional analyses identified enriched gene ontology (GO) terms and metabolic pathways related to the innate immune response and energy metabolism. Six functional candidate genes were identified for further functional and validation studies to better understand the underlying biological mechanisms of host responses to GINs. These, in turn, can potentially help improve decision making and management practices to increase the overall host immune response to GIN infection.

Anthelmintic effect of a water soluble Moringa oleifera lectin in rodents experimentally infected with Haemonchus contortus

Allied to the problem of gastrointestinal parasites, especially Haemochus contortus, the use of lectins of plant origin has contributed to the research of alternative anthelmintics. The nematicidal effect of a water soluble Moringa oleifera lectin (WSMoL) was investigated in an experimental model with H. contortus infected Wistar rodents. Three concentrations were tested orally: 5 mg/kg, 2.5 mg/kg and 1 mg/kg. The reduction in the number of larvae recovered in the experimental groups was analyzed, as well as biochemical, hematological and histological parameters. Treatments with 5, 2.5 and 1 mg/kg of WSMoL reduced the number of larvae recovered of animals by 74.7%, 72.8% and 66%, respectively. Untreated infected animals had anemia, moderate mononuclear multifocal hepatitis, vascular congestion in the liver and kidneys, white pulp hyperplasia in the spleen, and presence of eosinophils in the intestine. Infected animals treated with 5 mg/kg of WSMoL showed liver with moderate bleeding, kidney with vascular congestion, spleen with white pulp hyperplasia and intestine with moderate presence of mononuclear cells. An increase in the serum level of glutamic pyruvic transaminase and a reduction in the level of hemoglobin (p < 0.001) were also observed in this group when compared to the uninfected group. However, the administered concentrations of 2.5 and 1 mg/kg of WSMoL were both satisfactory in terms of reducing the number of recovered larvae and not promoting negative changes in the biochemical, hematological and histological parameters evaluated. These results indicate an in vivo nematicidal effect of WSMoL on the H. contortus parasite.

Genome-wide scan reveals important additive and non-additive genetic effects associated with resistance to Haemonchus contortus in Florida Native sheep

Florida Native sheep is among the sheep breeds best adapted to humid and hot climatic conditions such as those of Florida, USA, and have shown a superior ability to regulate nematode burdens. This is one of the oldest sheep breeds in North America and is an endangered species. To ensure genetic diversity and long-term survival of the breed, protection of the current genetic stock is critical and conservation efforts are required to promote its breeding and production. The objective of the present study was to investigate the importance of additive and non-additive genetic effects on resistance to natural Haemonchus contortus infections in Florida Native sheep using a whole genome scan. A total of 200 sheep were evaluated in the present study. Phenotypic records included faecal egg count (FEC, eggs/gram), FAMACHA® score, packed cell volume (PCV, %), body condition score and average daily gain (ADG, kg). Sheep were genotyped using the GGP Ovine 50K SNP chip and 45.2 k single nucleotide polymorphism (SNP) markers spanning the entire genome were available for quality control procedures. Mixed models were used to analyse the response variables and included the identity by state matrix to control for population structure. Bonferroni correction was used to control for multiple testing and a second arbitrary threshold (0.1 × 10^-3) was used. Fifteen SNPs with additive and non-additive genetic effects and located in Ovis aries chromosome OAR1, 2, 3, 6, 8, 10, 11, 12, 13 and 21 were associated with FEC, FAMACHA® score, PCV and ADG. These SNPs could be potential genetic markers for resistance to natural H. contortus exposure in Florida Native sheep.

Haemonchosis: A Challenging Parasitic Infection of Sheep and Goats

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

Biology, Epidemiology, and Control of Gastrointestinal Nematodes of Small Ruminants

Strongylid gastrointestinal nematodes are an important cause of disease and economic loss in small ruminants. These parasites are important in most of the United States, with the bloodsucking parasite Haemonchus contortus being the predominant species of concern. Sheep and goats are infected while grazing, and the biology of infective larvae on pastures is important in the design of parasite management programs. Widespread resistance to anthelmintics requires strategies designed to preserve remaining drug activity; these include combination treatments with multiple classes of anthelmintics and targeted treatments.

Association study reveals Th17, Treg, and Th2 loci related to resistance to Haemonchus contortus in Florida Native sheep1

The aim of this study was to identify for the first time single nucleotide polymorphisms (SNPs) associated with Haemonchus contortus resistance in Florida Native sheep, using a targeted sequencing approach. One hundred and fifty-three lambs were evaluated in this study. At the start of the trial, phenotypic records for fecal egg count (FEC), FAMACHA score, body condition score (BCS), and weight were recorded and deworming of sheep with levamisole (18 mg/kg of body weight) was performed. Ten days post-deworming (baseline) and 28 d post-baseline, a full hematogram of each sheep was obtained and FEC, FAMACHA score, BCS, and weight were assessed. Average daily gain was calculated at the end of the trial. Out of 153 animals, 100 sheep were selected for genotyping using a targeted sequencing approach. Targeted sequencing panel included 100 candidate genes for immune response against H. contortus. SNPs were discarded if call rate <95% and minor allele frequency ≤0.05. A mixed model was used to analyze the response variables and included the identity by state matrix to control for population structure. A contemporary group (age, group, and sex) was included as fixed effect. Bonferroni correction was used to control for multiple testing. Eighteen SNPs on chromosomes 1, 2, 3, 4, 6, 7, 11, 15, 18, 20, 24, and 26 were significant for different traits. Our results suggest that loci related to Th17, Treg, and Th2 responses play an important role in the expression of resistant phenotypes. Several genes including ITGA4, MUC15, TLR3, PCDH7, CFI, CXCL10, TNF, CCL26, STAT3, GPX2, IL2RB, and STAT6 were identified as potential markers for resistance to natural H. contortus exposure. This is the first study that evaluates potential genetic markers for H. contortus resistance in Florida Native sheep.

Signatures of selection for resistance to Haemonchus contortus in sheep and goats

Background

Gastrointestinal nematode infection (GNI) is the most important disease affecting the small ruminant industry in U.S. The environmental conditions in the southern United States are ideal for the survival of the most pathogenic gastrointestinal nematode, Haemonchus contortus. Host genetic variation for resistance to H. contortus allows selective breeding for increased resistance of animals. This selection process increases the prevalence of particular alleles in sheep and goats and creates unique genetic patterns in the genome of these species. The aim of this study was to identify loci with divergent allelic frequencies in a candidate gene panel of 100 genes using two different approaches (frequentist and Bayesian) to estimate Fst outliers in three different breeds of sheep and goats exposed to H. contortus.

Results

Our results for sheep populations showed SNPs under selection in C3AR1, CSF3, SOCS2, NOS2, STAT5B, TGFB2 and IL2RA genes using frequentist and Bayesian approaches. For goats, SNPs in CD1D, ITGA9, IL12A, IL13RA1, CD86 and TGFB2 genes were under selection. Common signatures of selection in both species were observed in NOS2, TGFB2 and TLR4 genes. Directional selection was present in all SNPs evaluated in the present study.

Conclusions

A total of 13 SNPs within 7 genes of our candidate gene panel related to H. contortus exposure were identified under selection in sheep populations. For goats, 11 SNPs within 7 genes were identified under selection. Results from this study support the hypothesis that resistance to H. contortus is likely to be controlled by many loci. Shared signatures of selection related to mechanisms of immune protection against H. contortus infection in sheep and goats could be useful targets in breeding programs aimed to produce resistant animals with low FEC.

Seasonal Dynamics of Gastrointestinal Nematode Infections of Goats and Emergence of Ivermectin Resistance in Haemonchus contortus in Hubei Province, China

INTRODUCTION

Gastrointestinal nematodes (GINs) are a major constraint to the survival and productivity of animals. In southern China, goats are the most important small domestic ruminants.

METHODS

From May 2013 to May 2017, we conducted a longitudinal study of hircine GIN infections in Huangshantou Town, Gongan County, Hubei Province, China, using fecal egg counts.

RESULTS

Our investigation revealed that the GINs of goats in Hubei Province have changed significantly. Over 90% of eggs detected in the first month of investigation, May 2013, belonged to the species Haemonchus contortus and Chabertia sp. There was no seasonal variation in positive rates (PRs) of GINs, but the mean eggs per gram (EPG) of GINs were higher between April and July than between September and November (P < 0.05). The gradual increase in the percentage of H. contortus eggs among all detected eggs during our research and the low cure rate of IVM mass treatment revealed the emergence of IVM resistance in H. contortus. After the implementation of an integrated GIN control strategy, which included two mass treatments (one in April/May with ABZ and another in September/October with IVM + ABZ), in 2016 and 2017, both the PRs and EPG of GINs were significantly reduced.

CONCLUSION

The results presented here reveal that controlling GINs of small ruminants in small farms in southern China requires an integrated control strategy that should include monitoring of infection and anthelmintic resistance, and increased farmer education on the importance of using the appropriate drugs at the correct dose.

Effect of Ovar-DRA and Ovar-DRB1 genotype in small ruminants with haemonchosis

The effect of Ovar-DRA and Ovar-DRB1 genotypes on faecal egg count (FEC) was determined in sheep and goats infected with Haemonchus contortus. One hundred and forty-three sheep from 3 different breeds (St. Croix, Katahdin and Dorper) and 150 goats from three different breeds (Spanish, Boer and Kiko) were used. Parasitological (FEC), haematological (packed cell volume) and immunological (IgA, IgG and IgM) parameters were measured. Sheep populations showed a higher FEC and humoural response than goat breeds. Genotypes were determined by high-resolution melting assays and by conventional PCR. For Ovar-DRA, sheep and goats carrying the AA genotype showed significant lower FEC than AG and GG genotypes. The additive effect was found to be 115.35 less eggs per gram of faeces for the A allele for goats. For Ovar-DRB1, only in sheep, the GC genotype was associated with low FEC. The additive effect was 316.48 less eggs per gram of faeces for the G allele, and the dominance effect was 538.70 less eggs per gram of faeces. The results indicate that single nucleotide polymorphisms within Ovar-DRA and Ovar-DRB1 could be potential markers to be used in selection programmes for improving resistance to Haemonchus contortus infection.

Effects of Feeding Garlic Powder on Growth Performance, Rumen Fermentation, and the Health Status of Lambs Infected by Gastrointestinal Nematodes

Simple Summary

Non-chemical strategies to control gastrointestinal nematodes (GINs) infection are urgently needed to support the sustainable development of the livestock industry. The potential anti-parasitic properties in garlic powder to control sheep GINs was investigated in this study. The key finding of this study was that feeding garlic powder increased growth performance of lambs infected with GINs by decreasing fecal egg counts and improving feed digestion, rumen fermentation, and the health status of lambs.

Abstract

For the study, forty lambs were weighed and assigned into two treatments to determine the effects of feeding garlic powder on growth performance, rumen fermentation, and the health status of lambs infected with gastrointestinal nematodes (GINs). The lambs were fed with a basal diet without or with 50 g/kg garlic powder for 84 d. Data were analyzed by a general linear or mixed model of SAS software and differences were considered statistically significant if p ≤ 0.05. Results showed that garlic powder supplementation increased the lambs’ average daily gain (p = 0.025), digestibility of dry matter (p = 0.019), and crude protein (p = 0.007). No significant changes were observed on the dry matter intake, feed conversion ratio, as well as the apparent digestibility of lipid and fiber. An interactive effect between treatment and feeding day was observed on ruminal pH (p < 0.001) and ammonia nitrogen concentration (p < 0.001). Ruminal pH (p < 0.001) and ammonia nitrogen concentration (p < 0.001) decreased with garlic powder supplementation, while ammonia nitrogen concentration increased (p = 0.001) with the extension of the feeding period. Garlic powder supplementation increased the total volatile fatty acid concentration (p < 0.001) in the rumen fluid, the molar proportion of acetic acid (p = 0.002), propionic acid (p < 0.001), and isovaleric acid (p = 0.049), but it decreased the ratio of acetic acid to propionic acid (p = 0.015). The lambs’ fecal egg count decreased (p < 0.001), but the packed cell volume and body condition scores of lambs increased (p < 0.001) with garlic powder supplementation. In conclusion, feeding garlic powder increased growth performance, feed digestion, rumen fermentation, and the health status of lambs infected with GINs.

Tropical plant supplementation effects on the performance and parasite burden of goats

Objective

Examine the effects of supplementing bahiagrass hay (BG) with potentially anthelmintic quantities of hays of perennial peanut (PEA) or sericea lespedeza (LES) or seeds of velvet bean (Mucuna pruriens L.; MUC) or papaya (PAP) on the intake and nutritive value (Experiment 1), and the performance and parasite burden (Experiment 2) of goats.

Methods

In Experiment 1, 38 male goats (27.4±5.7 kg body weight) were randomly assigned to each of 5 treatments: i) BG alone and BG plus; ii) PEA; iii) LES; iv) MUC; and v) PAP. Goats were fed for ad libitum consumption and adapted to the diets for 14 d followed by 7 d of measurement. The PEA, LES, MUC (50%, 50%, and 10% of the diet dry matter [DM], respectively), and PAP (forced-fed at 10 g/d) were fed at rates that would elicit anthelmintic effects. In Experiment 2, goats remained in the same treatments but were allocated to 15 pens (3 pens per treatment) from d 22 to 63. All goats were infected with parasites by grazing an infected bahiagrass pasture from 0800 to 1500 h daily and then returned to the pens.

Results

Dry matter intake tended to be greater in goats fed PEA and LES than those fed BG (757 and 745 vs 612 g/d, respectively). Digestibility of DM (59.5% vs 54.9%) and organic matter (60.8% vs 56.0%) were greater in goats fed MUC vs BG, respectively. In Experiment 2, feeding PAP, LES, and PEA to goats reduced nematode fecal egg counts by 72%, 52%, and 32%, reduced abomasal adult worm counts by 78%, 52%, and 42%, and decreased plasma haptoglobin concentrations by 42%, 40%, and 45% relative to feeding BG alone, respectively.

Conclusion

Supplementation with PEA, LES, and PAP decreased the parasite burden of goats but did not increase their performance. PAP was the most effective anthelmintic supplement.

Inheritance of faecal egg counts during early lactation in Scottish Blackface ewes facing mixed, natural nematode infections

This paper presents an analysis of nematode faecal egg counts from Scottish Blackface ewes facing mixed, natural nematode infections (predominantly Teladorsagia circumcincta). The data set comprised 1445 measurements on 421 ewes taken at 4 and 6 weeks post-lambing, over a 4-year period. The ewes, themselves, were the progeny of 73 sires and 285 dams. Only Strongyle eggs were consistently present, and faecal egg counts from this genera ranged from zero (0·4 of all measurements) to 3388 eggs per g. Faecal egg counts were significantly affected by the number of lambs reared and suckled (increasing reproductive burden led to higher counts) by ewe age (older ewes had lower counts) and by previous selection history (ewes from a line previously selected for increased carcass fatness had lower faecal egg counts than ewes from a conversely selected lean line). The heritability of log-transformed faecal egg counts was 0·23 (s.e. 005) and the repeatability, including both within- and between-year permanent environmental effects, was 0·25 (s.e. 004). The apparent presence or absence of infection had a heritability of 015 (s.e. 007) on the observed scale and 0·39 (s.e. 016) when analysed as a binomial threshold trait. The genetic correlation between average 4-week weight of lamb suckled by the ewe and faecal egg counts was 0·24 (s.e. 010). The results suggest that faecal egg counts during early lactation are heritable and influenced by the reproductive performance of the ewe. Selection to reduce nematode faecal egg output from ewes during this period should be successful in reducing pasture larval contamination.

Breeding for resistance to gastrointestinal nematodes - the potential in low-input/output small ruminant production systems

The control of gastrointestinal nematodes (GIN) is mainly based on the use of drugs, grazing management, use of copper oxide wire particles and bioactive forages. Resistance to anthelmintic drugs in small ruminants is documented worldwide. Host genetic resistance to parasites, has been increasingly used as a complementary control strategy, along with the conventional intervention methods mentioned above. Genetic diversity in resistance to GIN has been well studied in experimental and commercial flocks in temperate climates and more developed economies. However, there are very few report outputs from the more extensive low-input/output smallholder systems in developing and emerging countries. Furthermore, results on quantitative trait loci (QTL) associated with nematode resistance from various studies have not always been consistent, mainly due to the different nematodes studied, different host breeds, ages, climates, natural infections versus artificial challenges, infection level at sampling periods, among others. The increasing use of genetic markers (Single Nucleotide Polymorphisms, SNPs) in GWAS or the use of whole genome sequence data and a plethora of analytic methods offer the potential to identify loci or regions associated nematode resistance. Genomic selection as a genome-wide level method overcomes the need to identify candidate genes. Benefits in genomic selection are now being realised in dairy cattle and sheep under commercial settings in the more advanced countries. However, despite the commercial benefits of using these tools, there are practical problems associated with incorporating the use of marker-assisted selection or genomic selection in low-input/output smallholder farming systems breeding schemes. Unlike anthelmintic resistance, there is no empirical evidence suggesting that nematodes will evolve rapidly in response to resistant hosts. The strategy of nematode control has evolved to a more practical manipulation of host-parasite equilibrium in grazing systems by implementation of various strategies, in which improvement of genetic resistance of small ruminant should be included. Therefore, selection for resistant hosts can be considered as one of the sustainable control strategy, although it will be most effective when used to complement other control strategies such as grazing management and improving efficiency of anthelmintics currently.

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

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

Epizootological study of small ruminant gastrointestinal strongyles in Gamo-Gofa Zone, Southern Ethiopia

The study was conducted with the objective to estimate the prevalence of gastrointestinal strongyles and identifying the prevailing strongyle species Gamo-Gofa Zone. A total of 598 animals (241 sheep and 357 goats) and 45 animals (20 sheep and 25 goats) were examined coproscopically and by post mortem, respectively. The overall coproscopic prevalence of strongylosis in the study area was 51.4 %. Strongyles were more prevalent in sheep than goats (95 % CI is 74.6-84.8 % and 58.6-68.6 % for sheep and goats, respectively; P < 0.05). A higher prevalence (P < 0.05) of strongyles infection was recorded in the midland and highland than the lowland, and in wet season than the dry season. The mean fecal egg count was found to be significantly higher (P < 0.05) in the midland area (908.7 ± 94.5) and in wet season (1,033.7 ± 84.2). The post mortem examination result indicated that the overall prevalence of gastrointestinal strongyles was 97.7 %; and a total of 11 strongyle species were identified of which Trichostrongylus axei, Teladorsagia species, Trichostrongylus colubriformis and Haemonchus contortus were the dominant and with higher load. During this study infection with multiple parasites, 3 and more 3, species were recorded in about 68 % goats and 85 % sheep. This study revealed the very high strongyle prevalence and higher proportion of multiple parasitism both in sheep and goats. Hence, it suggests the need to the institution of various control measures like strategic anthelmintic treatment for efficient utilization of the available small ruminant resources.

Effects of supplementation with dietary green tea polyphenols on parasite resistance and acute phase protein response to Haemonchus contortus infection in lambs

The objective of this study was to determine the effects of supplementation with dietary green tea polyphenols (GTPs) on parasite resistance and acute phase protein (APP) response to Haemonchus contortus infection in lambs. Thirty male Ujumqin lambs were randomly assigned to five treatment groups for an 8-week feeding period. Treatments included: (1) uninfected as control, (2) infected but not given GTP (INFGTP0) and (3)-(5) infected and fed 2, 4, or 6g GTP/kg feed (dry matter basis; INFGTP2, INFGTP4, and INFGTP6, respectively). Fecal and blood samples were collected to determine fecal egg count (FEC), packed cell volume (PCV), and APP concentrations. Live weight was measured once every 2 weeks. At the end of the feeding period, lambs were slaughtered to determine the adult H. contortus burden. The results demonstrated interaction effects between treatment and sampling time on the average daily gain (ADG; P=0.0005), FEC (P<0.0001), PCV (P=0.0005), and concentrations of serum amyloid A (SAA), haptoglobin (Hp), lipopolysaccharide binding protein (LBP), and α1-acid glycoprotein (α1AGP) (P<0.0001). From days 0 to 56, the ADG values for all infected lambs were lower than that of uninfected lambs, but the ADG values for all GTP-fed lambs were higher than that of INFGTP0 lambs, especially from days 28 to 42. The FECs of all GTP-fed lambs were higher than those of uninfected lambs but lower than that of INFGTP0 lambs. The PCVs of all infected lambs were lower than those of uninfected lambs, but PCV increased with increasing amounts of GTP supplementation. Furthermore, supplementation with different concentrations of GTP significantly reduced the numbers of adult H. contortus, including both males and females (P<0.0001), and the H. contortus burden in INFGTP6 lambs was reduced to uninfected levels. Overall, the SAA, Hp, LBP, and α1AGP concentrations of all infected lambs were higher than those of uninfected lambs from days 0 to 56. Two peaks in expression were observed from days 0 to 3 and at day 28, and APP concentrations of all GTP-fed lambs were lower than those of INFGTP0 lambs, except for SAA in INFGTP6 lambs. In conclusion, quantitative measurements of APP responses to H. contortus infection provide valuable diagnostic information for monitoring infection progression and treatment responses in lambs. An appropriate dose of dietary GTP supplementation can increase host resistance by reducing H. contortus burden and weight loss and suppressing blood APP expression.

Effects of tannic acid on Haemonchus contortus larvae viability and immune responses of sheep white blood cells in vitro

Direct inhibitory effects of tannic acid on Haemonchus contortus viability were studied in vitro using the larval migration inhibition (LMI) assay. Sheep white blood cells (WBC) were preincubated with 5 and 50 lg/mL tannic acid or not followed by whole H. contortus antigen (WHA). Cells were harvested at 24 h post-incubation to test host immune responses. Concentrations of 50, 100, 500, 1000, 3000 and 5000 lg/mL tannic acid inhibited larvae migration by 19.8, 42.4, 46.3, 92.0, 93.7 and 100%, respectively, within 96 h post-incubation (P < 0.001). The relative mRNA levels of interferon (IFN)-c, interleukin (IL)-2, IL-4 and IL-10 were increased by WHA stimulation without tannic acid. However, the increased effects on IFN-c and IL-2 were inhibited by tannic acid preincubation (P < 0.001), while the increases in IL-4 and IL-10 were greatly enhanced by tannic acid preincubation (P < 0.001). Changes in protein levels of all cytokines essentially paralleled the changes in their corresponding mRNA levels. In conclusion, tannic acid is directly harmful to larvae in a dose- and time-dependent manner and modulates immune responses of sheep WBC stimulated by H. contortus antigen by inhibiting Th1 cytokines and increasing Th2 cytokine expression in vitro.

Integrated control of gastrointestinal nematodes in lambs using a bioactive feed × breed approach

Forages rich in condensed tannins have repeatedly shown potential to reduce gastrointestinal nematode infection in sheep. Similarly, several breeds of sheep have shown a relative resistance to gastrointestinal nematodes (GIN). We hypothesised that additive or even synergic effects may arise from the combination of a relatively resistant breed and a diet rich in condensed tannins. In study I, 160 lambs of the native Red Engadine Sheep (RES) and 113 lambs of the Swiss White Alpine sheep (SWA) were artificially infected with GIN and subsequently grazed for 52 days. The lambs were then distributed to 2 groups for a 14-day experimental feeding period. One group received a diet with a proportion of 55% sainfoin and was compared to a control group on the basis of faecal egg counts (FEC). In study II, 25 RES and 27 SWA lambs grazed infectious pastures for 37 days and were subsequently fed for 13 consecutive days with approximately 100% sainfoin or control forage. In addition to the FEC determination at the start and the end of the experimental feeding, the 52 lambs in study II were slaughtered and necropsied to determine their worm burden. FEC at the end of the feeding period were significantly lower in sainfoin fed lambs compared to controls in study I (p<0.001) as well as in study II (p=0.012). Breed, animal age, live weight, sex and the interaction of breed and treatment did not affect FEC in either study. The main nematode genera found in the sacrificed lambs of study II were Haemonchus spp., Teladorsagia spp., Nematodirus spp. and Trichostrongylus spp. Overall, RES had a significantly lower Haemonchus spp. (p=0.035) and Trichostrongylus spp. (p=0.003) worm burden compared to SWA. Regardless of breed, sainfoin feeding significantly reduced Teladorsagia spp. (p=0.049) and Nematodirus spp. (p<0.001) worm burden. Although, we could not demonstrate additive or synergic effects when using an integrated breed × sainfoin approach, the finding that a proportion of only 55% sainfoin in the diet led to a lower FEC compared to controls is important with respect to the implementation on producing farms.

Immune responses associated with resistance to haemonchosis in sheep

This paper examines the known immunological and genetic factors associated with sheep resistance to infection by Haemonchus contortus. Such resistance is an inheritable genetic trait (h², 0.22–0.63) associated with certain sheep breeds. Resistant sheep do not completely reject the disease; they only harbor fewer parasites than susceptible sheep and therefore have a lower fecal egg count. Protective immune response to haemonchosis is an expression of genetic resistance. Genes associated with resistance and susceptibility are described. Genetically resistant sheep have nonspecific mechanisms that block the initial colonization by Haemonchus contortus larvae. These sheep also have an efficacious Th2 type response (e.g., increases in blood and tissue eosinophils, specific IgE class antibodies, mast cells, IL-5, IL-13, and TNFα) that protects them against the infection; in contrast, susceptible sheep do not efficiently establish this type of immune response. Finally, the main reported antigens of H. contortus were reviewed.

Detecting genes for variation in parasite burden and immunological traits in a wild population: testing the candidate gene approach

Identifying the genes underlying phenotypic variation in natural populations can provide novel insight into the evolutionary process. The candidate gene approach has been applied to studies of a number of traits in various species, in an attempt to elucidate their genetic basis. Here, we test the application of the candidate gene approach to identify the loci involved in variation in gastrointestinal parasite burden, a complex trait likely to be controlled by many loci, in a wild population of Soay sheep. A comprehensive literature review, Gene Ontology databases, and comparative genomics resources between cattle and sheep were used to generate a list of candidate genes. In a pilot study, these candidates, along with 50 random genes, were then sequenced in two pools of Soay sheep; one with low gastrointestinal nematode burden and the other high, using a NimbleGen sequence capture experiment. Further candidates were identified from single nucleotide polymorphisms (SNPs) that were highly differentiated between high- and low-resistance sheep breeds. A panel of 192 candidate and control SNPs were then typed in 960 individual Soay sheep to examine whether they individually explained variation in parasite burden, as measured as faecal egg count, as well as two immune measures (Teladorsagia circumcincta-specific antibodies and antinuclear antibodies). The cumulative effect of the candidate and control SNPs were estimated by fitting genetic relationship matrices (GRMs) as random effects in animal models of the three traits. No more significant SNPs were identified in the pilot sequencing experiment and association study than expected by chance. Furthermore, no significant difference was found between the proportions of candidate or control SNPs that were found to be significantly associated with parasite burden/immune measures. No significant effect of the candidate or control gene GRMs was found. There is thus little support for the candidate gene approach to the identification of loci explaining variation in parasitological and immunological traits in this population. However, a number of SNPs explained significant variation in multiple traits and significant correlations were found between the proportions of variance explained by individual SNPs across multiple traits. The significant SNPs identified in this study may still, therefore, merit further investigation.

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

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

Tracking the emergence of a new breed using 49,034 SNP in sheep

Domestic animals are unique in that they have been organised into managed populations called breeds. The strength of genetic divergence between breeds may vary dependent on the age of the breed, the scenario under which it emerged and the strength of reproductive isolation it has from other breeds. In this study, we investigated the Gulf Coast Native breed of sheep to determine if it contains lines of animals that are sufficiently divergent to be considered separate breeds. Allele sharing and principal component analysis (PCA) using nearly 50,000 SNP loci revealed a clear genetic division that corresponded with membership of either the Florida or Louisiana Native lines. Subsequent analysis aimed to determine if the strength of the divergence exceeded that found between recognised breed pairs. Genotypes from 14 breeds sampled from Europe and Asia were used to obtain estimates of pair-wise population divergence measured as F(ST). The divergence separating the Florida and Louisiana Native (F(ST) = 6.2%) was approximately 50% higher than the average divergence separating breeds developed within the same region of Europe (F(ST) = 4.2%). This strongly indicated that the two Gulf Coast Native lines are sufficiently different to be considered separate breeds. PCA using small SNP sets successfully distinguished between the Florida and Louisiana Native animals, suggesting that allele frequency differences have accumulated across the genome. This is consistent with a population history involving geographic separation and genetic drift. Suggestive evidence was detected for divergence at the poll locus on sheep chromosome 10; however drift at neutral markers has been the largest contributor to the genetic separation observed. These results document the emergence of populations that can be considered separate breeds, with practical consequences for bio-conservation priorities, animal registration and the establishment of separate breed societies.

Small ruminant resistance against gastrointestinal nematodes: a case of Haemonchus contortus

Gastrointestinal nematode (GIN) infections are a common constraint to small ruminant industry throughout the world, and among those, haemonchosis has its own significance. Control of GIN primarily relies on the use of anthelmintics, but this approach has become less reliable due to the development of resistance in GINs against commonly used anthelmintics and an increased consumer demand for environmentally friendly animal products. These issues have stimulated investigations to find alternative sustainable control strategies, which are less reliant on anthelmintic input. One of such strategies is breeding of small ruminants for their resistance to the GINs. The susceptibility and resistance of animals to GIN infections varies within and between breeds. Various parasitological, biochemical and immunological parameters are employed to evaluate natural resistance status of animals both in natural pasture and artificial infections. The immune mechanisms responsible for resistance are not completely understood, but it has a significant effect in inherited resistance. Relatively resistant or tolerant animals show better local and generalised immune response as compared to susceptible. Immune response against GINs is influenced by many physiological factors. Determination of specific genes linked with host resistance will provide a valuable approach to find out the molecular mechanism of host resistance to GINs. Resistance has been reported to reduce pasture contamination, which in turn reduces re-infection and thus the requirement of the frequent anthelmintic treatments. The efficiency of control can be increased through objective and accurate identification of genetically tolerant individuals by natural and artificial infections with GINs. Complete resistance is the ultimate solution, but this has generally been ignored as a commercial reality. This paper reviews the published reports on natural resistance in small ruminants and discusses the prospects of developing small ruminants, which could be resistant to GINs.

Combinação de drogas antiparasitárias como uma alternativa para o controle de nematódeos gastrintestinais multirresistentes em ovinos

Este estudo foi realizado com o objetivo de encontrarem-se tratamentos anti-helmínticos eficazes sobre uma população de nematódeos gastrintestinais de ovinos, a qual desenvolveu resistência a todas as classes de drogas com ação nematicida disponíveis para ruminantes no mercado brasileiro. Valendo-se da eficácia calculada de tratamentos convencionais a partir de um estudo prévio e, assim, conhecendo-se sua ação sobre diferentes gêneros de nematódeos presentes no rebanho, selecionaram-se drogas as quais, utilizadas em combinações ou em altas doses, pudessem aumentar significativamente a eficácia dos tratamentos. Utilizou-se o percentual de redução da contagem de ovos nas fezes e as culturas de larvas para avaliar a ação anti-helmíntica dos tratamentos testados. A combinação de moxidectina 1% + disofenol 20% apresentou 99% de eficácia, e as combinações de moxidectina 1% + triclorfon 10% e de moxidectina 1% + fosfato de levamisol 22,3% superaram os 90% de eficácia. A utilização de combinações de princípios ativos, com diferentes mecanismos de ação, pode promover a recuperação da eficácia dos tratamentos anti-helmínticos sobre populações multirresistentes de nematódeos gastrintestinais de ovinos.

A comparison of two integrated approaches of controlling nematode parasites in small ruminants

Control of gastrointestinal nematodes (GIN) in small ruminants in regions of the world where anthelmintic resistance is prevalent must rely on more than just chemical deworming strategies. The objective of this experiment was to compare two integrated treatment protocols for control of GIN (primarily Haemonchus contortus in this region) using anthelmintics, copper oxide wire particles (COWP) and FAMACHA(©), compared to traditional anthelmintic use only. Three separate trials were conducted on mature ewes, weaned goats, and weaned lambs in which three deworming management strategies were applied: 1) all animals were dewormed with levamisole at four week intervals (LEV), 2) individual animals were dewormed with moxidectin when scored≥4 (ewes) or ≥3 (kids and lambs) using FAMACHA(©) (FAM/MOX), 3) all animals were dewormed with moxidectin initially and again with COWP (2g) when group mean FEC exceeded 500 (ewes), 3000 (kids), or 1000 (lambs) eggs/g (MOX/COWP). In this final group, during periods between group treatments, individual animals were dewormed with albendazole and levamisole according to FAMACHA(©) score. Fecal egg counts (FEC) and blood packed cell volume (PCV) were determined every 7 days and body weight every 28 days for 30, 20, or 16 weeks in ewes, goats, and lambs, respectively. Efficacy of levamisole was 83.4-86.4%, efficacy of moxidectin was 93.5-100%, and efficacy of COWP was 10.8-98.1% among the three trials. The mean number of deworming treatments per animal that occurred for the LEV, FAM/MOX, and MOX/COWP groups, respectively, was 7.9, 0.6, and 2.5±0.4 (P<0.001) for ewes, 5.2, 1.6, and 3.4±0.3 (P<0.001) for goats, and 4.0, 1.7, and 3.6±0.2 (P<0.001) for lambs. Production (body weight of lambs weaned from ewes or final body weight of kids and lambs) was similar among management strategy groups for ewes and kids, but FAM/MOX lambs were lighter by the end of the trial (P<0.003). While more time and labor was required to use the FAMACHA(©) system, a more conservative use of anthelmintics occurred in the FAM/MOX group.

Comparison of parasitological and productive traits of Criollo lambs native to the central Mexican Plateau and Suffolk lambs experimentally infected with Haemonchus contortus

The study compares the parasitological and productive traits of Criollo lambs native to the central Mexican Plateau (CNCMP) and Suffolk (SU) lambs experimentally infected with Haemonchus contortus. CNCMP lambs (n=20) and SU lambs (n=15) were infected with L3 of H. contortus while five lambs of each genotype were kept as controls. Fecal egg count (FEC), packed cell volume (PCV), blood eosinophil number (BEN), ocular mucous membrane color (as measured by the FAMACHA index), changes in body condition score (BCS) and cumulative live weight gain (CLWG) were measured weekly during a 20-week period. On week 20, all animals were euthanized and the number of adult worms (AW) in the abomasum was counted. Infected SU lambs had higher (p<0.05) FEC and AW mean values compared to CNCMP lambs, which had a higher mean BEN count (p<0.05). Infected lambs had lower PCV values than controls, regardless of genotype, and had a negative correlation (r=-0.84, p<0.05) with the FAMACHA index. BCS tended to decline for infected SU lambs and increased slightly for infected CNCMP lambs. CLWG differed in all groups (p<0.05); infected SU lambs gained 12.1+/-1.9kg, infected CNCMP lambs gained 18.8+/-0.7kg, control SU lambs gained 34.6+/-1.6kg, and control CNCMP lambs gained 26.9+/-0.8kg. In conclusion, CNCMP lambs had a smaller worm burden, a better ability to maintain their productive traits, and were less affected by infection with Haemonchus contortus.

Effect of feeding bioactive forages on infection and subsequent development of Haemonchus contortus in lamb faeces

Contrasting dried herbage diets were offered to lambs to evaluate their effects on Haemonchus contortus infection and on subsequent development of larvae in faeces. Artificially infected lambs (n=24, 4 months old) were allocated to one of four treatment groups (n=6) and fed on hay of lucerne (Medicago sativa; Lu), sulla (Hedysarum coronarium; Su), sainfoin (Onobrychis viciifolia; Sa) or wormwood (Artemisia absinthium; Wo) included as 20% in ground lucerne pellets. While voluntary intake was similar, lamb growth rates were notably affected by diet. Additionally, necropsies carried out 30 days post-infection showed that worm burden was reduced by 8 (Su), 13 (Sa) and 49% (Wo) with respect to that found in lambs fed on lucerne, though only the difference with wormwood was significant. Faecal egg excretion expressed on a dry matter basis was also reduced by 22 (Su), 54 (Sa) and 73% (Wo), but differences were significant only for wormwood and sainfoin, which was associated with a decrease in female fecundity. Sulla and sainfoin diets significantly reduced egg hatching rates but increased the percentage of L(3) in the faeces of the host animal, particularly in the case of sulla hay compared to other forages. Consequently, the potential risk of infection derived from faecal excretion could be notably altered. Further work is needed to validate these findings and their implications in an applied farming system.

Parasitological and clinical responses of lambs experimentally infected with Haemonchus contortus (L3) with and without ivermectin treatment

Haemonchus contortus is one of the most important parasites that infects sheep and exerts its pathogenic effects by sucking blood, causing disturbances of organ-functions and thus inducing alterations in various normal physiological parameters. Changes in live body weight, faecal egg count, kinetics of circulating eosinophils and PCV value were studied at weekly interval for a period of 84 days in 18 lambs of local breed after infection with a single dose of 5000 H. contortus (L(3)). In the two groups of lambs infected with nematodes both non-treated and treated with ivermectin (HcNT and HcIT), similar egg excretion patterns was observed starting from third week after infection, with a regular increase in FEC. Examination of whole abomasum of each animal revealed no developmental stage of nematode from treated and control lambs on day 84. The total mean number of H. contortus worms recovered at necropsy from abomasa of untreated infected lambs (group HcNT) was 2576.2 (+/-221.0). The significant loss of body weight, development of heavy worm burden and severe anaemia as indicated by reduced PCV in untreated infected lambs indicated high susceptibility of the lambs to H. contortus. On the other hand, complete absence of the parasite, improved PCV value and body weight after treatment of infected animals (HcIT) proved 100% efficacy of ivermectin against H. contortus.

A Th2 type of immune response is associated with increased resistance to Haemonchus contortus in naturally infected Gulf Coast Native lambs

Haemonchus contortus is one of the major nematode parasites causing substantial economic losses in small ruminant farming worldwide. Recently, effectiveness of anthelmintic treatment has decreased due to an increasing problem of nematode populations that have developed resistance to anthelmintics. Efforts to develop effective vaccines have had limited success. There are certain breeds of sheep that are relatively resistant to the parasite including Gulf Coast Native (Native) sheep. Understanding the protective nature of the immune response that helps these breeds of sheep control infection could enable the development of vaccines to enhance control programs. This experiment was designed to compare the immunological responses of resistant Native versus susceptible Suffolk sheep in order to identify the mechanisms responsible for this resistance. Immune responses were evaluated in naturally infected Native and Suffolk lambs that grazed pasture contaminated predominantly with H. contortus. Ten lambs of each breed grazed together for 42 days. Fecal, blood and serum samples were collected on 0, 2, 4, 7, 10, 14, 21, 28, 35 and 42 days of exposure. Five lambs of each breed were necropsied on day 35 and five on day 42 for nematode recovery and abomasal tissue sample collection. Throughout the course of infection, Native lambs had significantly lower FEC, significantly lower PCV reduction percent, and significantly higher serum IgE after day 14 and increased expression of IL-4 on day 10 post-exposure compared to Suffolk lambs. At both necropsy time points, Native lambs had significantly greater numbers of mucosal mast cells, eosinophils and globule leukocytes in abomasal mucosa than Suffolk lambs. Results indicated that Native lambs had a more pronounced immune response to infection with H. contortus than Suffolk lambs which may be responsible for the observed resistance to infection.

Influence of periparturient nutritional demand on resistance to parasites in livestock

Periparturient relaxation of immunity (PPRI) to gastrointestinal nematode parasites may have a nutritional basis, as the increasing nutrient demand at times of nutrient scarcity during late pregnancy and subsequent lactation may result in a penalty on expression of acquired immunity to parasites. This nutritional basis implies that lowering nutritional demand, at constant nutrient supply, should reduce the degree of PPRI. Evidence to support the latter is reviewed through exploration of the effects of reproductive effort on periparturient resistance to parasites. A large body of evidence shows that a lower nutritional demand arising from rearing single rather than multiple lambs and/or kids consistently reduces the degree of PPRI in small ruminants, as manifested by reduced worm burdens and/or nematode egg excretions. Such variation in reproductive effort may also account, at least to some extent, for the often observed between-breed differences in PPRI, which may arise from differences in production potential, and thus nutritional demand. A reduction in nutrient demand can reduce the degree of PPRI in a matter of days. However, host immune responses associated with this nutritional sensitivity of host resistance remain to be elucidated, which may be achieved through a recently established periparturient rodent model.

Breed differences in mucosal and systemic antibody response to nematode infection in sheep: an important role for IgE?

This study compared the immunological and biochemical responses of co-grazed Suffolk and Texel lambs to a natural gastrointestinal nematode infection. Variables analysed included serum pepsinogen, total protein, albumin, haematological variables and nematode-specific serum immunoglobulin activity, at 11, 14 and 17 weeks of age. At 17 weeks, randomly selected lambs were necropsied to determine worm burdens, nematode-specific mucosal abomasal and intestinal immunoglobulin activity. Nematode burden, faecal egg count and pepsinogen concentrations were significantly higher in Suffolks relative to Texels, at all 3 time-points investigated. Suffolks displayed significantly higher erythrocyte, total leukocyte, lymphocyte and neutrophil counts, mean cell volume and packed cell volume, than Texels (P<0·01). However, breed differences in eosinophil counts were not significant. While serum nematode-specific antibody activity levels were significantly higher (P<0·001) in Texels for all isotypes measured, antibody activity levels at a mucosal level were equivalent in both breeds. Correlation analysis of mucosal antibody levels and nematode variables highlighted a more consistent pattern of events in Texels, with more mucosal antibodies negatively correlated with FEC and worm burden, in comparison to Suffolks. In particular, an important role for mucosal IgE is proposed. In Texels, a significant and negative correlation was identified between IgE and faecal egg counts and worm burden (FEC: −0·48, P<0·005). This was not observed in Suffolks. The evidence suggests that susceptibility in Suffolks may be mediated through poor IgE affinity/avidity and/or through deficiencies in related mechanisms such as mast cell production, recruitment or activation.

A model to account for the consequences of host nutrition on the outcome of gastrointestinal parasitism in sheep: logic and concepts

A deterministic, dynamic simulation model is developed to account for the interactions between gastrointestinal parasitism and host nutrition, and predict their consequences on performance and level of parasitism of sheep. Larval intake and established adult worms are assumed to result in nutrient loss for the host. In order to reduce this loss the host will mount an immune response, which will affect the establishment rate of incoming larvae, mortality rate of adult worms, and fecundity of female worms, as well as nutrient loss caused by larval intakeper se. Host anorexia is modelled as a function of worm mass. Parasitism is also assumed to affect the allocation of ingested nutrients to the host's bodily functions, with maintenance getting absolute priority, and protein allocated to immunity and production proportionally to their requirements. Inputs to the model include the expected growth attributes of the animal, feed quality, various parasitological parameters and daily larval intake. Outputs include feed intake, growth rate and body composition, as well as worm burden and faecal egg counts. The model allows exploration of the consequences of gastrointestinal parasitism on sheep of different growth characteristics, kept under environments that vary in the provision of nutrients and exposure to parasites.

Gastrointestinal nematodes of small ruminants: life cycle, anthelmintics, and diagnosis

Strongylid gastrointestinal nematodes are an important cause of disease and economic loss in small ruminants. These parasites are particularly important in the eastern United States where the bloodsucking parasite Haemonchus contortus is the predominant species. Sheep and goats are infected with gastrointestinal nematodes while grazing and the biology of the infective larvae on the pastures is important in planning effective control programs. Fecal egg counts can be used to monitor control programs and drug efficacy and evaluate levels of pasture contamination.

Anthelmintic resistance and alternative control methods

Anthelmintic resistance has been a problem almost from the first use of the drugs introduced during the past 50 years. Evaluation of anthelmintics on a specific farm is essential to determine which drugs may be used in controlling parasite numbers. Treatment of livestock during the season in which parasite transmission is unfavorable lessens pasture contamination. Targeting treatment places less pressure on susceptible worms, diluting the resistant parasite population. Pasture management and using safe pastures for animals at highest risk lower pasture exposure. Selection for individual animals resistant to the effects of parasites lessens the need for use of anthelmintics. Alternatives to anthelmintics include cryptic antigen vaccines, copper wires, and biologic compounds.

Quality and freezing qualities of first and second ejaculates collected from endangered Gulf Coast Native rams

The Gulf Coast Native sheep, or Louisiana Native sheep, is an endangered previously feral domestic sheep population of European origin that has been under natural selection pressure for reproductive survival in their transplanted range while roaming in the southern Gulf Coast Region of the United States. This sheep population has an increased natural resistance to internal parasites, breeds year-around and has a greater percentage of live lambs as compared with other breeds of sheep raised in similar environments. To preserve the genetic diversity of this important feral sheep population, semen was collected by electro-ejaculation and subjected to cryopreservation for subsequent storage in a genome resource bank. Unrelated rams (n=5) were collected 3 days-a-week, allowing at least 2 days of rest between collections. Two ejaculates were obtained from each ram per collection day, with the second collection conducted 10min after the first ejaculation. Semen was processed using the standard Salamon cryopreservation procedure in a Tris-yolk-glycerol extender, frozen in 0.5ml plastic straws using liquid nitrogen (LN(2)) vapor and stored in LN(2). Each ejaculate was evaluated for volume, sperm concentration/ml (x10(9)/ml), number of spermatozoa/ejaculate (x10(9)), sperm progressive motility (%) for pre-cooled semen, cooled semen and semen after thawing. For the five rams, each semen variable for the first ejaculate was compared with that of the second ejaculate collected 10min later. The mean semen volume, sperm concentration and number of spermatozoa per ejaculate obtained from the first ejaculate were significantly greater (P< or =0.01) than those of the second ejaculate (comparisons being 1.62 and 1.06; 3.2 and 1.5; 5.4 and 1.8, respectively). Overall, the mean motility of pre-cooled (22 degrees Celsius), cooled (5 degrees Celsius) and frozen (-196 degrees Celsius) post-thawed spermatozoa was less (P< or =0.01) in the first ejaculate (71.5, 64.8 and 34.1%, respectively) compared with that of the second ejaculate (75, 72.4 and 44.1%, respectively). Conversely, no differences were detected in loss in the percent progressive motility of sperm from cooled sperm to post-thaw sperm from the first and second ejaculates. In summary, our findings suggest sperm collected during the second ejaculate 10min after the first ejaculate of rams survives thawing with a greater rate of progressive motility than that of the first ejaculate. The ability to collect two consecutive ejaculates in a short period by electro-ejaculation could be valuable for gamete resource banking and preserving genetic diversity of the Gulf Coast Native sheep.

Epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep in a semi-arid region of eastern Ethiopia

A study on the epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep was carried out in a semi-arid region of eastern Ethiopia for 2.5 years (May 2003 to September 2005). The experimental flock comprised a total of 60 Black Head Ogaden sheep, consisting of four equal groups of young male and female and old male and female sheep. These grazed on communal pastures together with a larger university flock, as well as with animals owned by neighbouring small-holder farmers. A new experimental flock was established each year of the study. Parasitological data (EPG, faecal culture L3, PCV and FAMACHA estimates) and animal performance (weight change) were recorded each month on all experimental animals. In addition, four tracer lambs were assigned each month to the flock to determine the seasonal patterns of infective larvae acquired from pasture. Results showed distinct seasonal patterns associated with the bi-modal annual rainfall. High levels of infection occurred during the short and long rain seasons with peaks occurring in May and September of each year. Haemonchus contortus was the most prevalent parasite, followed by Trichostrongylus spp., with a number of other nematode species being occasionally recorded. H. contortus showed and increased propensity to undergo arrested development during the dry seasons. Correlations between EPG and PCV, EPG and FAMACHA eye scores, and PCV and FAMACHA eye scores were all highly significant (P<0.001). However, there was no significant association between the EPG and LW of the study animals during each study year. This information will provide a basis for developing epidemiologically based control strategies for gastrointestinal nematode parasites that are appropriate for flocks owned by small-holder farmers of semi-arid areas of eastern Ethiopia.

Survey of helminths in adult sheep in Heilongjiang Province, People's Republic of China

The prevalence of helminths in adult sheep was investigated in Heilongjiang Province, People's Republic of China between January 1999 and September 2003. A total of 326 adult sheep representing local breeds (Xingjiang Fine Wool Sheep, Dongbei Fine Wool Sheep) as well as introduced breeds (Merino and Charollais) from representative geographical locations in Heilongjiang Province were slaughtered and examined for the presence of helminths. The worms were examined, counted and identified to species according to existing keys and descriptions. A total of 26 helminth species were found representing 2 phyla, 3 classes, 13 families and 20 genera. All sheep were infected by more than one helminth species. Oesophagostomum columbianum, Haemonchus contortus and Trichostrongylus colubriformis were the most common nematode species, and Paramphistomum cervi, Orientobilharzia turkestanica and Fasciola hepatica were the most common trematode species, whereas the infection of adult sheep with cestodes was uncommon. The results of the present investigation provide relevant "base-line" data for Heilongjiang Province, China, for assessing the effectiveness of future control strategies against helminth infections in sheep.

Segregation of natural and experimental gastrointestinal nematode infection in F2 progeny of susceptible Suffolk and resistant Gulf Coast Native sheep and its usefulness in assessment of genetic variation

Gastrointestinal nematode parasitism is a concern to small ruminants worldwide. Productivity has been compromised because such nematodes, particularly Haemonchus contortus, have developed resistance to available anthelmintics. Some sheep breeds and lines within breeds are relatively resistant to infection, a trait that may be useful for developing control strategies. Suffolk sheep, which are susceptible to infection, were crossed with Gulf Coast Native sheep, which are more resistant to infection, to produce F1 progeny. F1 rams were bred to F1 ewes which produced 227 F2 offspring. These F2 offspring were evaluated for variability in infection levels, based on fecal egg count (FEC) and blood packed cell volume (PCV), under two natural infection conditions (one at weaning and another after a summer grazing period) and one experimental infection. The range of both FEC and PCV was large for all three infection periods with annual variation. Overall, the range for the three infection periods, respectively, were 167-149,933, 0-31,400 and 17-114,667 eggs per gram (EPG) of feces and 8.7-37.0%, 7.3-33.0% and 8.3-36.0%. This segregation of infection is what would be expected of F(2) progeny from susceptible and resistant parent breeds. Heritabilities of FEC and PCV for the three infection periods, respectively, were 0.15, 0.29 and 0.12, and 0.11, 0.22 and 0.12. Based on segregation of infection, larger heritabilities and maternal environment effects that declined after weaning, the summer natural infection was probably the best model for assessing genetic variation.

Effect of nutritional status and fat reserves on the periparturient immune response to Haemonchus contortus infection in sheep

A study was made of the effect of body fat stored by ewes in early pregnancy on the subsequent immune response to gastrointestinal parasites around parturition. Pregnant ewes were given access to a lucerne pelleted diet either ad libitum (H) or at approximately 0.70 of their maintenance requirements (L) from the 42nd day of pregnancy in order to achieve a clearly differentiated level of body reserves by the 90th day of pregnancy. Then, all animals were put on the same plane of nutrition till 3 weeks after parturition. All ewes in both groups received 7,000 infective larvae of Haemonchus contortus per week for 7 weeks prior to lambing. The dietary treatments led to large differences between both groups of ewes in back-fat thickness that had a high correlation with mean plasma concentrations of leptin. In spite of the fact that animals were on the same plane of nutrition at infection time, host resistance, as measured by faecal egg counts, was significantly affected by the nutritional treatment established during early pregnancy. This effect produced noticeable differences in worm size and in worm burden at lambing. The response was accompanied by a marked increase in circulating eosinophils in better-fed ewes than in those maintained on a restricted diet in early pregnancy. Serum pepsinogen concentration, however, was inversely affected by the nutritional treatment till lambing, showing a maximum difference as early as 2 weeks after infection. The results support the view that higher levels of nutrition during early pregnancy enhance the expression of immunity against gastrointestinal parasites around parturition. Furthermore, the differences in the immune response appeared associated with serum leptin levels suggesting that leptin may be a key link between nutritional status and the protective immune reactivity against GI nematode infection.

Effect of CD4+ T lymphocyte depletion on resistance of Gulf Coast Native lambs to Haemonchus contortus infection

It has been reported that CD4(+) T lymphocytes are important in acquired immunity to gastrointestinal nematode infection. Whether these lymphocytes are also involved in the immune response of naturally resistant Gulf Coast Native (GCN) sheep to Haemonchus contortus infection remains to be defined. The objective of this study was to determine the role of CD4(+) T lymphocytes in this resistance. Ten GCN lambs were randomly assigned to a control (n=5) or a treatment (n=5) group. The treatment consisted of a series of IV injections with mouse anti-ovine CD4(+) T lymphocyte monoclonal antibodies for a period of 3 weeks. After the second treatment, all lambs were experimentally infected with 10,000 H. contortus infective larvae by oral inoculation. All lambs were monitored for fecal egg counts, blood packed cell volumes, white blood cell differential counts and serum antibody responses on a weekly basis. Fluorescence-activated cell sorter (FACS) analysis was done biweekly to enumerate CD4(+) T lymphocytes in peripheral blood. Necropsies were performed at the end of the study and 10% of the contents of the gastrointestinal tract were preserved for nematode enumeration and identification. Also at necropsy, mesenteric lymph nodes were extracted and FACS analysis was run on lymphoid cells. Mean fecal egg counts on day 21 and 28 post-infection and nematode counts at necropsy of the treated group were significantly (p<0.05) higher than that of the control group. Percent CD4(+) T lymphocytes in peripheral blood was significantly (p<0.05) lower in the treatment group than in the control group from day 9 to the end of the study. No differences were found in blood packed cell volumes, white blood cell differential counts, antibody titer or lymph node CD4(+) lymphocytes between groups. Lambs depleted of their CD4(+) T lymphocytes were more susceptible to H. contortus infection than undepleted lambs. The results of this study suggest that CD4(+) T lymphocytes are associated with the natural resistance of GCN sheep to H. contortus infection.

Haemonchus contortus (Nematoda: Trichostrongylidae) infection in lambs elicits an unequivocal Th2 immune response

Selection of resistant animals and host immunization have been proposed as alternative methods for the control of gastrointestinal nematode parasites. However, a better knowledge of the mechanisms involved in protective immunity against these parasites is required for the development of optimal strategies. In this study, 3 month old INRA 401 lambs (n = 81) were allocated into three groups: uninfected control, challenged either once (primary-infected animals) or twice (previously-infected animals) with 10,000 Haemonchus contortus L3. Uninfected control and challenged animals were sequentially sacrificed at 3, 7, 15 and 28 days post challenge. In both challenged groups, a clear Th2-oriented immune response was observed in the abomasal lymph node and mucosa. IL-4 and IL-13 mRNA over-expression, recruitment of eosinophils, mast cells and globule leukocytes and production of specific systemic IgG and mucosal IgA were observed earlier in previously-infected animals than in primary-infected ones. At 28 days post infection, no differences between intensities of these responses were observed between the challenged groups. Worm establishment rates were similar in previously-infected and primary-infected lambs. However, reductions of worm development, female fecundity and fecal egg output were observed in previously-infected sheep. We conclude that H. contortus infection in young INRA 401 lambs induced an unequivocal Th2 immune response resulting in the regulation of worm egg production without affecting their establishment.