Age-dependent immune response in Merino sheep

Review: Environmental enrichment builds functional capacity and improves resilience as an aspect of positive welfare in production animals

The success of the animal in coping with challenges, and in harnessing opportunities to thrive, is central to its welfare. Functional capacity describes the capacity of molecules, cells, organs, body systems, the whole animal, and its community to buffer against the impacts of environmental perturbations. This buffering capacity determines the ability of the animal to maintain or regain functions in the face of environmental perturbations, which is recognised as resilience. The accuracy of physiological regulation and the maintenance of homeostatic balance underwrite the dynamic stability of outcomes such as biorhythms, feed intake, growth, milk yield, and egg production justifying their assessment as indicators of resilience. This narrative review examines the influence of environmental enrichments, especially during developmental stages in young animals, in building functional capacity and in its subsequent expression as resilience. Experience of enriched environments can build skills and competencies across multiple functional domains including but not limited to behaviour, immunity, and metabolism thereby increasing functional capacity and facilitating resilience within the context of challenges such as husbandry practices, social change, and infection. A quantitative method for measuring the distributed property of functional capacity may improve its assessment. Methods for analysing embedded energy (emergy) in ecosystems may have utility for this goal. We suggest functional capacity provides the common thread that links environmental enrichments with an ability to express resilience and may provide a novel and useful framework for measuring and reporting resilience. We conclude that the development of functional capacity and its subsequent expression as resilience is an aspect of positive animal welfare. The emergence of resilience from system dynamics highlights a need to shift from the study of physical and mental states to the study of physical and mental dynamics to describe the positive dimension of animal welfare.

Molecular detection and associated risk factors of Anaplasma marginale, A. ovis and A. platys in sheep from Algeria with evidence of the absence of A. phagocytophilum

Anaplasma species are obligate intracellular rickettsial pathogens that cause significant diseases in animals and humans. Despite their importance, limited information on Anaplasma infections in Algeria has been published thus far. This study aimed to assess the infection rate, characterize Anaplasma species, and identify associated risk factors in selected sheep farms across Oum El Bouaghi region in Algeria. In 2018, we collected 417 blood samples from sheep (Ovis aries) and performed molecular characterization of Anaplasma species infecting these animals. This characterization involved the use of 16S rRNA, msp2, rpoB, and msp5 genes, which were analyzed through nested PCR, qPCR, cPCR, DNA sequencing, and subsequent phylogenetic analysis. Our findings revealed infection rates of 12.7 % for Anaplasma species detected, with Anaplasma ovis at 10.8 %, Anaplasma marginale at 1.7 %, and Anaplasma platys at 0.2 %. Interestingly, all tested animals were found negative for Anaplasma phagocytophilum. Statistical analyses, including the Chi-square test and Fisher exact test, failed to establish any significant relationships (p > 0.05) between A. ovis and A. platys infections and variables such as age, sex, sampling season, and tick infestation level. However, A. marginale infection exhibited a significant association with age (p < 0.05), with a higher incidence observed in lambs (5.2 %) compared to other age groups. Remarkably, this study represents the first molecular detection of A. platys and A. marginale in Algerian sheep. These findings suggest that Algerian sheep may serve as potential reservoirs for these pathogens. This research contributes valuable insights into the prevalence and characteristics of Anaplasma infections in Algerian sheep populations, emphasizing the need for further investigation and enhanced surveillance to better understand and manage these diseases.

The prevalence of intestinal parasite infections in goats from smallholder farms in Northern Thailand

The present study determined the prevalence of gastrointestinal (GI) parasites in small ruminants kept in smallholder farms in Phitsanulok, Northern Thailand. A total of 885 goats from 31 smallholder farms were selected randomly between May 2019 to January 2020. Fecal samples were collected to estimate fecal egg counts and oocysts counts using the modified McMaster technique. Furthermore, pooled fecal samples from each of the farms were cultured in order to differentiate third-stage larvae of nematode. Examination of fecal samples revealed that 885 were positive for one or more parasites, giving an overall prevalence of 87.2 %, of which 38.6 % were infected with one and 48.6 % with multiple parasite. Strongyles and Eimeria oocysts were the most prevalent. Haemonchus contortus and Strongyloides papillosus were the predominant species based on the percentage of larvae in fecal cultures. Tapeworm eggs were encountered in 14.2 % of all samples. No significant difference in gastrointestinal parasite prevalence was associated with sex of the host. Infection was significantly (P = 0.009) highest in poor body conditioned goats (72.0 %) as compared to moderate (48.9 %) and good body conditioned (50.0 %) goats. This report on prevalence of GI parasites of small ruminants in smallholder farms in Northern Thailand reveals a high endoparasitic infections that appeared well-adapted to environmental conditions. Further studies on endoparasite control are required to establish the impact of parasitism on productive performance, including monitoring control parasite programs are needed for better health and productivity.

Dermatophilosis (lumpy wool) in sheep: a review of pathogenesis, aetiology, resistance and vaccines

Lumpy wool (dermatophilosis) develops following prolonged wetting of sheep when bacterial proliferation in wool and on skin induce an exudative dermatitis, causing a superficial skin lesion and damage to wool follicles and fibres. The incidence of dermatophilosis is strongly dependent on wet and warm weather and, hence, infection is sporadic. While older animals are less at risk than are lambs, it is unclear whether this reflects naturally acquired immune resistance or the maturation of skin and wool fibres. Dermatophilosis directly causes wool production losses and it also is a risk factor for blowfly strike, which has a substantial economic impact and increasing challenges associated with current control procedures. This review assessed research on the bacterial causes of lumpy wool, the characteristics of the resulting immune defence reactions in sheep, current control strategies, and limitations of previous attempts to control lumpy wool by sheep vaccination.

Fleece rot and dermatophilosis (lumpy wool) in sheep: opportunities and challenges for new vaccines

During prolonged wetting of the fleece, proliferation of bacterial flora often dominated by Pseudomonas aeruginosa or Dermatophilus congolensis can induce dermatitis and fleece damage termed fleece rot and dermatophilosis respectively, which predispose sheep to blowfly strike. A large research effort in the 1980s and 1990s on vaccines to control fleece rot and dermatophilosis met with limited success. This review examines theoretical and technological advances in microbial ecology, pathogenesis, immunology, vaccine development and the characterisation of microbial virulence factors that create new opportunities for development of vaccines against these diseases. Genomic technologies have now created new opportunities for examining microbial dynamics and pathogen virulence in dermatitis. An effective vaccine requires the combination of appropriate antigens with an adjuvant that elicits a protective immune response that ideally provides long-lasting protection in the field. A clinical goal informed by epidemiological, economic and animal welfare values is needed as a measure of vaccine efficacy. Due to dependence of fleece rot and dermatophilosis on sporadic wet conditions for their expression, vaccine development would be expedited by in vitro correlates of immune protection. The efficacy of vaccines is influenced by genetic and phenotypic characteristics of the animal. Advances in understanding vaccine responsiveness, immune defence in skin and immune competence in sheep should also inform any renewed efforts to develop new fleece rot and dermatophilosis vaccines. The commercial imperatives for new vaccines are likely to continue to increase as the animal welfare expectations of society intensify and reliance on pharmacotherapeutics decrease due to chemical resistance, market pressures and societal influences. Vaccines should be considered part of an integrated disease control strategy, in combination with genetic selection for general immune competence and resistance to specific diseases, as well as management practices that minimise stress and opportunities for disease transmission. The strategy could help preserve the efficacy of pharmacotherapeutics as tactical interventions to alleviate compromised welfare when adverse environmental conditions lead to a break down in integrated strategic disease control. P. aeruginosa and D. congolensis are formidable pathogens and development of effective vaccines remains a substantial challenge.

Are Vaccines the Solution for Methane Emissions from Ruminants? A Systematic Review

Ruminants produce considerable amounts of methane during their digestive process, which makes the livestock industry as one of the largest sources of anthropogenic greenhouse gases. To tackle this situation, several solutions have been proposed, including vaccination of ruminants against microorganisms responsible for methane synthesis in the rumen. In this review, we summarize the research done on this topic and describe the state of the art of this strategy. The different steps implied in this approach are described: experimental design, animal model (species, age), antigen (whole cells, cell parts, recombinant proteins, peptides), adjuvant (Freund's, Montanide, saponin, among others), vaccination schedule (booster intervals and numbers) and measurements of treatment success (immunoglobulin titers and/or effects on methanogens and methane production). Highlighting both the advances made and knowledge gaps in the use of vaccines to inhibit ruminant methanogen activity, this research review opens the door to future studies. This will enable improvements in the methodology and systemic approaches so as to ensure the success of this proposal for the sustainable mitigation of methane emission.

Morada Nova sheep breed: Resistant or resilient to Haemonchus contortus infection?

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Resistance against Haemonchus contortus was assessed in a Morada Nova flock.

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More than 88% of the lambs had PCV ≥ 24% even with high fecal egg counts (FEC).

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Only susceptible lambs had decreased live weight due to parasitism.

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More than 98% of the ewes had FEC below 4000 EPG.

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PCV of the ewes was not affected by H. contortus infection.

Morada Nova is a Brazilian hair sheep breed that is well adapted to the country’s mainly tropical climate and has good potential for meat and leather production. This breed is reported to be resistant to Haemonchus contortus infection, a highly desired characteristic due to the large impact of this parasite on sheep farming. Therefore, the present study aimed to characterize 287 recently weaned Morada Nova lambs and 123 ewes in relation to their resistance against H. contortus. The animals were dewormed and 15 days later artificially infected with 4000 H. contortus L₃ (D0). They were individually monitored by periodic assessment of fecal egg count (FEC), packed cell volume (PCV), and live weight (LW). On D42, the sheep were again dewormed and submitted to a new parasitic challenge, following the same scheme. The animals of each category (lambs and ewes) were ranked according to individual mean FEC values, and classified as resistant (R, 20%), intermediate (I, 60%), or susceptible (S, 20%) to H. contortus infection. At weaning, high FEC were observed in all three phenotypes (P > 0.05). After the artificial infections, there was a significant difference (P < 0.05) among the three lamb phenotypes for the mean FEC (R < I < S), PCV (R > I > S), and LW (R = I > S). The infection levels (FEC) were negatively correlated with PCV (r = -0.66; P < 0.001), and LW (r = -0.30; P < 0.001). Despite this, the lambs were resilient, since more than 88% of these animals maintained the PCV above 24%, even when heavily infected. The importance of selective parasite control before weaning to reduce the negative impact on slaughter weight was evidenced, taking into account the high positive correlation between LW at weaning and final LW (r = 0.73; P < 0.001). The ewes, in turn, were strongly resistant to the parasite. Despite highly significant differences (P < 0.001) for mean FEC between phenotypes (R < I < S), 98% of the ewes maintained FEC below 4000 EPG. Their health was not affected, since PCV and LW did not differ between phenotypes, and these parameters were not significantly correlated with FEC (P > 0.05). With the phenotypic characterization performed here, it is possible to introduce procedures for parasite control in Morada Nova flocks, facilitating the target-selective treatment approach. The results of this study can also support improvement of meat production by the Morada Nova breed.

Cellular and humoral immunity in a wild mammal: Variation with age & sex and association with overwinter survival

Immune defenses are expected to be crucial for survival under the considerable parasite pressures experienced by wild animals. However, our understanding of the association between immunity and fitness in nature remains limited due to both the complexity of the vertebrate immune system and the often‐limited availability of immune reagents in nonmodel organisms. Here, we use methods and reagents developed by veterinary researchers for domestic ungulates on blood samples collected from a wild Soay sheep population, to evaluate an unusually broad panel of immune parameters. Our evaluation included different innate and acquired immune cell types as well as nematode parasite‐specific antibodies of different isotypes. We test how these markers correlate with one another, how they vary with age‐group and sex, and, crucially, whether they predict overwinter survival either within or among demographic groups. We found anticipated patterns of variation in markers with age, associated with immune development, and once these age trends were accounted for, correlations among our 11 immune markers were generally weak. We found that females had higher proportions of naïve T cells and gamma–delta T cells than males, independent of age, while our other markers did not differ between sexes. Only one of our 11 markers predicted overwinter survival: sheep with higher plasma levels of anti‐nematode IgG antibodies were significantly more likely to survive the subsequent high mortality winter, independent of age, sex, or weight. This supports a previous finding from this study system using a different set of samples and shows that circulating antibody levels against ecologically relevant parasites in natural systems represent an important parameter of immune function and may be under strong natural selection. Our data provide rare insights into patterns of variation among age‐ and sex groups in different T‐cell subsets and antibody levels in the wild, and suggest that certain types of immune response—notably those likely to be repeatable within individuals and linked to resistance to ecologically relevant parasites—may be most informative for research into the links between immunity and fitness under natural conditions.

Relative maturity and the development of immunity to gastrointestinal nematodes in sheep: an overlooked paradigm?

Sheep display considerable variation in both the timing and magnitude of development of immunity to gastrointestinal nematodes (GIN). Onset of immunity is dependent on a number of factors, including antigenic stimulus, nutrition supply, age and size of the animals, the latter of which are confounded. Here, we review the factors associated with the development of immunity to GIN in sheep, particularly in the context of the role that relative maturity may have through applying the rules of genetic size scaling based on examples from published literature. Comparing animals based on their metabolic age, rather than chronological age, may provide an explanation for the timing of immune development and may reduce the variation in immune development that frequently is observed both between and within breeds. Further, this approach may help explain the phenotypic differences in animal performance between animals of varying immunological capacity to GIN through influences on mature body weight. As such, when considering factors influencing immune development to GIN, physiological age or relative maturity may be considered an overlooked paradigm. We propose it may be worthwhile to consider metabolic age when comparing the immune competence of animals to ensure the subjects are at an analogous stage of physiological development.

The heritability of abortion in pedigree Charollais flocks

Foetal death, or abortion at term, in sheep is of major significance to the livestock industry, accounting for more than £24million lost per annum. We have investigated whether there is a genetic component to abortion within two flocks of pedigree Charollais sheep, one followed from 1989 to 2006, the other from 1992 to 2006. Abortion occurred at a rate of 5.74-8.78% per annum against a total mortality rate of 14-24%. By model covariate analysis we have shown that 15.5% aborting ewes went on to have one or more abortions and that this risk increased with parity (p=0.006). Heritability estimates were approximately 0.08 as calculated by SOLAR, pedigreemm and ASReml3, with sire and dam components of 0.046 and 0.048, respectively. Where the lamb was aborted, heritability estimates were highly variable according to the method employed, 0.046-0.378, with sex of the lamb being a significant covariate. This variability indicated one or more underlying, significant factors that were not measured in these analyses, potentially including infectious agents that may be involved. Nevertheless, the ASReml3 estimate (0.179) resolved to 0.074 variance attributable to the sire and 0.092 attributable to the dam, which, while not significant, was suggestive that genetic variants passed by the dam to the lamb may be of more weight than that from the sire in determining whether a lamb will abort.

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.

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.

Effects of Teladorsagia (Ostertagia) circumcincta infection on lambs selected for high fleece weight

The physiological processes leading to the expression of the resilient phenotype, which allow animals to maintain a relatively higher production level during infection, have been investigated in lambs from a closed flock selected for 40 generations for high fleece weight (HFW), but with higher FEC and worm burdens than their unselected control (C) flock run in parallel. After recovery from surgery to implant abomasal cannulae, eight parasite-naive lambs from each flock were infected intraruminally at 4.5 months-of-age with 50,000 Teladorsagia circumcincta L3. Blood, abomasal fluid and faecal samples were collected daily for measurement of serum gastrin and pepsinogen concentrations, blood eosinophils, abomasal pH and FEC. Four lambs from each flock were euthanased on Day 8 post-infection and the other four on Day 28 post-infection. At necropsy, abomasal contents and tissues were collected for worm counts, abomasal lymph nodes and fundic tissue for cytokine gene expression and fundic tissue for histopathology. Expression of resilience appeared to be age-dependent as there were no significant differences in either FEC or worm burden between lambs from the two flocks, unlike older HFW lambs in a previous study. Abomasal secretion did not differ between flocks. Histopathological changes were typical of parasitism: inflammatory cells, mainly eosinophils and lymphocytes, were numerous in nodular areas and there were fewer TGF-alpha positive parietal cells, many of which were vacuolated. By Day 28 p.i., globule leucocytes were present. Mucosal thickness was significantly greater on Day 8 than Day 28 p.i. (p=0.000) and in C than HFW lambs. There were fewer parietal cells on Day 28 than on Day 8 p.i. (p=0.003) for pooled data. Circulating eosinophil counts increased moderately in both groups, significantly less in the HFW lambs. Fewer tissue and blood eosinophils in the HFW than C group on Day 8 p.i. were consistent with cytokine gene expression patterns, particularly lower IL-5 levels. Worm count decreased by 90% by Day 28 p.i., along with declining tissue eosinophil counts and IL-13 gene expression and increasing IL-10 and IL-4 gene expression. Food intake was depressed less in the HFW lambs, suggesting that maintenance of appetite could be an important aspect of the physiological basis for resilience. Although the resilient phenotype was not apparent at the younger age, lesser effects on food intake, differences in ALN cytokine profiles and lower blood and tissue eosinophil numbers in the HFW lambs may lead to the expression of resilience when older.

Six costs of immunity to gastrointestinal nematode infections

The strength of the immune response and the outcome of the interaction of a host with a parasite are influenced by genetic and phenotypic characteristics of both parties, and by environmental variables. Allocation of host resources to immune defence reduces resources available for other life-history traits. This review identifies six potential costs to the host from immune activation. The costs are likely to be broadly applicable to other immune responses in vertebrate species. Five phenotypic costs arise from: (i) increased metabolic activity; (ii) reduced nutrient availability due to anorexia; (iii) altered priorities for nutrient utilization; (iv) change in size and turnover of pools of immune cells and proteins; and (v) immunopathology from inappropriate or excessive immune activation. Subsumed by these costs is the cost of altered efficiency of nutrient use. A sixth cost is the genetic cost which arises from a change in the capacity of offspring to express production and life-history traits following selection for parasite resistance. The sensitivity of immune responses to the phenotypic status of the host, and the role the immune system shares with the neuroendocrine system in controlling use of resources underpin the importance of immunocompetence to the life-history of the host.

Immunohistochemical evaluation of inflammatory infiltrate in the skin and lung of lambs naturally infected with sheeppox virus

The present study describes immunophenotypic characteristics of inflammatory infiltrate in the skin and lung of lambs naturally infected with sheeppox virus (SPV). Three lambs revealed typical cutaneous and pulmonary lesions of sheeppox. Histologically, cutaneous and pulmonary lesions consisted of hyperplastic and/or degenerative changes in the epithelium with mononuclear cells, neutrophils, and typical sheeppox cells (SPCs), which had a vacuolated nucleus and marginated chromatin with occasional granular intracytoplasmic inclusions. The inflammatory infiltrate in pox lesions in both skin and lung was characterized by the presence of MHC II+ dendritic cells, CD4+, CD8+, gammadelta+ T cells, IgM+ cells, and CD21+ cells. Loss of expression of MHC I and MHC II antigens was observed in the affected areas of skin and lung. SPCs, stained with anti-SPV antibody, were also positive for CD14 and CD172A, antigens expressed on monocytes and macrophages. CD14 and CD172A negative SPCs were considered to be SPV infected degenerated epithelial cells or fibroblasts.

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.

Immune pre-activation exacerbates hemorrhagic brain injury in immature mouse brain

Premature infants with placental infection and adult stroke patients with fever have worse outcomes following intracerebral hemorrhage (ICH). We hypothesized that immune pre-activation would aggravate brain injury in mouse brain following ICH. The immune system of 2-day, 10-day and 7-week young adult CD1 mice was stimulated by intraperitoneal injection of concanavalin A (ConA), lipopolysaccharide (LPS) or polyinosinic-polycytidilic acid (PolyI:C) 12 h prior to intracerebral injection of blood. Two days later, brain damage and inflammation were worse in 2-day mice that had received LPS. The other agents had less consistent effects in 2-day mice. Brain damage in young adults was aggravated less after immune stimulation. These data suggest that immune pre-activation modifies hemorrhagic brain injury in immature mouse brain.

The effect of dietary polyunsaturated fatty acids (PUFA) on infection with the nematodes Ostertagia ostertagi and Cooperia oncophora in calves

Diet-induced changes in the polyunsaturated fatty acid (PUFA) content of immune cells influences the immune phenotype that develops following infection. The aim of this study was to examine the effect of manipulating dietary PUFA supply on tissue fatty acids composition and immunity to a mixed infection with an abomasal and an intestinal nematode parasite in calves. Calves (n=24) were allocated into two treatment groups and fed 25 g/day of either fish oil (n-3 group) or a binary mixture of palm/rapeseed oil (normal group) as a supplement in milk replacer. Within each treatment group eight calves were infected with 2000 L3 Ostertagia ostertagi and Cooperia oncophora, three times per week for 8 weeks, the remaining calves were pair-fed uninfected controls. Faecal egg counts (FEC) were carried out twice weekly. At slaughter, the whole gut was removed intact for worm counts and tissue samples were taken for fatty acid analysis. Samples of abomasum, duodenum and mid-gut were also collected for immunohistological analysis. FEC were not significantly influenced by oil supplement but tended to remain higher in the palm/rapeseed oil-fed group (normal infected). The number of intestinal immature worms was significantly (p<0.05) higher in the n-3 group. Mucosal mast cell (MMC) and eosinophil numbers were significantly increased (p<0.05) by infection and were significantly lower (p<0.05) in the intestinal tissue of the fish oil supplemented and infected group (n-3 infected group). These results suggest that feeding an n-3 PUFA-rich supplement (fish oil) can influence cellular mediators of immunity to nematode infection. This is the first report of the establishment of patency and the subsequent development of immunity to a mixed infection with O. ostertagi and C. oncophora in calves undergoing early rumen development. The trend in the FEC, MMC and eosinophil numbers in the n-3 group suggests that decreasing the dietary n-6/n-3 PUFA ratio may be a worthwhile immunonutritional strategy for potentiating the immune response to nematode parasite infection in the calf.

Vaccination-induced protection of lambs against the parasitic nematode Haemonchus contortus correlates with high IgG antibody responses to the LDNF glycan antigen

Lambs respond to vaccination against bacteria and viruses but have a poor immunological response to nematodes. Here we report that they are protected against the parasitic nematode Haemonchus contortus after vaccination with excretory/secretory (ES) glycoproteins using Alhydrogel as an adjuvant. Lambs immunized with ES in Alhydrogel and challenged with 300 L3 larvae/kg body weight had a reduction in cumulative egg output of 89% and an increased percentage protection of 54% compared with the adjuvant control group. Compared to the adjuvant dimethyl dioctadecyl ammonium bromide, Alhydrogel induced earlier onset and significantly higher ES- specific IgG, IgA, and IgE antibody responses. In all vaccinated groups a substantial proportion of the antibody response was directed against glycan epitopes, irrespective of the adjuvant used. In lambs vaccinated with ES in Alhydrogel but not in any other group a significant increase was found in antibody levels against the GalNAcbeta1,4 (Fucalpha1,3)GlcNAc (fucosylated LacdiNAc, LDNF) antigen, a carbohydrate antigen that is also involved in the host defense against the human parasite Schistosoma mansoni. In lambs the LDNF-specific response increased from the first immunization onward and was significantly higher in protected lambs. In addition, an isotype switch from LDNF-specific IgM to IgG was induced that correlated with protection. These data demonstrate that hyporesponsiveness of lambs to H. contortus can be overcome by vaccination with ES glycoproteins in a strong T-helper 2 type response-inducing aluminum adjuvant. This combination generated high and specific antiglycan antibody responses that may contribute to the vaccination-induced protection.

BOVIGAM: an in vitro cellular diagnostic test for bovine tuberculosis

BOVIGAM which is based on the detection of gamma interferon (IFN- gamma) is a rapid, laboratory assay of a cell mediated immune response that may be used for the detection of tuberculosis (TB) infection in animals. Whole blood is first incubated overnight with bovine PPD, avian PPD or negative control antigens, and IFN- gamma in the supernatant plasma is then measured by EIA. TB infection is indicated by a predominant IFN- gamma response to bovine PPD. Since 1988, BOVIGAM has been extensively trialed on more than 200 000 cattle in Australia, Brazil, Ireland, Northern Ireland, Italy, New Zealand, Romania, Spain and the USA. Sensitivity has varied between 81.8% and 100% for culture-confirmed bovine TB and specificity between 94% and 100%. The IFN- gamma assay detects M. bovis infection earlier than the skin test and in New Zealand is applied to detect skin-test negative cattle with TB, where after slaughter a significant number of IFN- gamma reactors have TB. BOVIGAM is also approved in New Zealand for serial testing skin test positive cattle when non-specificity is suspected. Cattle are tested 7-30 days after a positive caudal fold test. The boosting effect of the skin test on T-cell activity allows blood to be cultured with PPD up to 30 h after collection without effecting accuracy. The BOVIGAM results are not affected by poor nutritional condition and are only mildly and briefly affected by dexamethasone treatment and parturition. IFN- gamma responses of cattle vaccinated with BCG are dose-dependent and short-lived. The BOVIGAM kit is now used routinely in many countries for the detection of M. bovis infected cattle, buffalo and goats.

Age-related protective immunity after vaccination with Haemonchus contortus excretory/secretory proteins

Protection against an experimental challenge infection by immunization with excretory/secretory products (ES) from Haemonchus contortus, containing predominantly proteins of 15 and 24 kDa, depends on the age of the sheep. Vaccinated sheep 9 and 6 months of age had reduced final worm burdens of 82 and 77, respectively. No reduction in worm burden was found in 3-month-old lambs. Nine-month-old sheep had significantly higher ES-specific serum immunoglobulin (Ig)G1 and IgA during immunizations and after challenge infection than 3-month-old lambs. There was no correlation within the 9-month-old sheep between ES-specific IgA or IgG1 levels and protection, measured as worm burden. However, when the different age groups were combined, negative correlations between percentage protection and ES-specific IgA and IgG1 levels after challenge were found. At the end of the experiment, peripheral blood eosinophils and mast cell counts in abomasal tissue were also significantly higher in the vaccinated and challenged 9-month-old sheep than in the vaccinated and challenged 3-month-old or than in the 9-month-old sheep with challenge, but without vaccination. The responses measured in young lambs were similar to the responses in sheep, but the height of these responses was in general of a lower magnitude.

Antibody response in sheep following immunization with Streptococcus bovis in different adjuvants

Recent studies have shown that immunization with Streptococcus bovis using Freund's complete adjuvant (FCA) may confer protection against lactic acidosis in sheep. The major objective of this study was to compare the antibody responses to S. bovis in a practically acceptable adjuvant (Freund's incomplete adjuvant (FIA); QuilA; dextran sulphate (Dex); Imject Alum; or Gerbu) and in FCA. Thirty-five sheep were randomly allocated to 7 treatment groups. Six groups were immunized with S. bovis in an adjuvant; the other group served as the non-immunization control. The primary immunization was administered intramuscularly on day 0. followed by a booster injection on day 28. Immunization with FCA induced the highest saliva and serum antibody responses. The saliva antibody concentrations in the FIA and QuilA groups were significantly higher than those in the Alum, Dex and Gerbu groups (p < 0.01). The serum antibody concentration in the FIA group was significantly higher than those in the QuilA, Alum. Dex and Gerbu groups (p < 0.01). Immunization enhanced the antibody level in faeces (p < 0.05), but there was no significant difference between the different adjuvant groups (p > 0.05). Seven and 14 days following booster immunization, the saliva antibody levels induced by QuilA and/or FIA were comparable with the level stimulated by FCA (p > 0.05). There was a strongly positive correlation (R2 = 0.770, p < 0.01) between the antibody concentrations in salival and serum. Compared with the controls, a higher faecal dry matter content was observed in the animals immunized with either FCA or QuilA. The change in faecal dry matter content was positively associated with the faecal antibody concentration (R2 = 0.441, p < 0.05). These results indicate that FIA and QuilA were effective at inducing high levels of antibody responses to S. bovis, and suggest that either Freund's incomplete adjuvant or QuilA may be useful for preparing a practically acceptable vaccine against lactic acidosis.

Protection in lambs vaccinated with Haemonchus contortus antigens is age related, and correlates with IgE rather than IgG1 antibody

Protection by vaccination with excretory-secretory products (ES) from Haemonchus contortus, containing predominantly proteins of 15 and 24 kDa, against an experimental challenge infection depends on the age of the sheep. Vaccinated sheep 9, 6 or 3 months of age were protected for 83%, 77% and -34%, respectively. There was a significant difference in ES-specific serum IgE response but not in IgG1 response, after the last vaccination between the different age groups. In the protected 9-month-old animals, there was an increase up to 18 times the prevaccination levels, while the increase in the unprotected 3-month-old animals was at most 1.4 times. The 6-month-old animals showed an intermediate increase of approximately six times the prevaccination level. There was no correlation within the 9-month-old sheep between ES-specific IgE levels and protection, measured as worm burden. However, when the different age groups were combined, there was a positive correlation (r = 0.38) between protection and ES-specific IgE levels 1 week after the vaccination. At the end of the experiment, peripheral blood eosinophils and mast cell counts in abomasal tissue were also significantly higher in the vaccinated and challenged 9-month-old sheep than in the vaccinated and challenged 3-month-old or than in the 9-month-old sheep with challenge, but without vaccination. Increased serum IgE levels, eosinophilia and mucosal mast cell hyperplasia are the hallmarks of a Th2 response and were all demonstrated in protected, older sheep, but not in unprotected, younger sheep.

Prominence of gammadelta T cells in the elicitation phase of dinitrochlorobenzene-induced contact hypersensitivity in lambs

Immunohistochemical techniques were used to identify T-cell subpopulations in the ear skin of lambs during the elicitation phase of dinitrochlorobenzene (DCNB)-induced contact hypersensitivity. Thirty lambs (21-26 weeks of age) were divided into groups of 10. The shaved right ear of one group was treated with DNCB. Two weeks later, this group was challenged with DNCB. One group was treated with the vehicle alone, and the remaining group was left untreated. The lambs were killed 48 hours after challenge, and tissue specimens were collected from the ears of the three groups. There was an increase in T-cell populations in the skin of the DNCB-treated lambs 48 hours after challenge. The majority of the T cells were CD8+ and associated predominantly with the blood vessels and adnexa of the superficial dermis. There was also an increased presence of CD4+ cells and gammadelta T cells in the superficial dermis. In the epidermis, clusters of gammadelta T cells and CD4+ cells were associated with microlesions. Computer-assisted morphometric analysis was used to estimate the relative presence of the T-cell subpopulations in the superficial and deep dermis and the entire dermis. Statistical analysis of the relative area of immunostaining showed that the significant increases in all T-cell subpopulations (CD4+, CD8+, and gammadelta T cells) in the entire dermis were accounted for by changes in the superficial dermis. The prominence of gammadelta T cells in delayed-type hypersensitivity in the skin of domestic ruminants has been the subject of conflicting reports. In the present study, CD4+ cell and gammadelta T-cell populations were of similar size in the normal and DNCB-treated lambs, suggesting an equal participation in the elicitation phase of contact hypersensitivity.

The distribution of lymphocyte subsets in normal ovine skin

The distribution of lymphocyte subsets in the skin of clinically normal sheep was studied using monoclonal antibodies to OvCD5, OvCD4, OvCD8, WC1, and CD45RA. Four different anatomical sites were examined in each of 38 sheep. Four different age groups ranging from 7 to 10-day-old lambs to 12 to 14-month-old adults were represented. The majority of lymphocytes in all age groups and at all sites were angiocentrically located within the superficial dermis. Total lymphocyte numbers at each site increased with age. The predominant cell type identified at all sites was WC1+ and the proportion of lymphocytes of this phenotype was significantly higher at wooled sites. Only occasional CD45RA +/- cells were present in any section.

Immunisation of sheep by drug-abbreviated infections of Ostertagia circumcincta and Trichostrongylus colubriformis against field challenge of gastro-intestinal nematodes

A very high level of protection was achieved against homologous (up to 97%) and heterologous (up to 87%) infections in 12-month-old Romney sheep immunised with oxfendazole-abbreviated infections of Ostertagia circumcincta and Trichostrongylus colubriformis. No significant protection occurred following ivermectin-abbreviated infections. None of the immunised sheep showed an increase in antibody level against excretory-secretory antigen of T. colubriformis infective larvae. The immunisation procedures did not cause a decrease in wool production, or liveweight gains compared with non-immunised controls.

Some relationships between age, immune responsiveness and resistance to parasites in ruminants

In the Australian livestock industries, susceptibility to infectious diseases is generally greater in young than in mature ruminants. The increased susceptibility is manifest as respiratory and intestinal infections (viral and bacterial) of calves, as well as fleece rot, flystrike and, especially, gastrointestinal parasitic infestations of young sheep. Lower resistance to infectious disease in young ruminants appears to be due largely to immunological hyporesponsiveness, and is not simply a consequence of their not having been exposed sufficiently to pathogens to develop active immunity. Young sheep have significantly lower proportions of CD4+ and CD8+ lymphocytes, but similar proportions of T19+ and B lymphocytes in blood, lymph and skin compared with mature sheep. Blood lymphocytes from young sheep produce less interferon-gamma in culture and young sheep invariably mount smaller antibody responses than do mature animals. Taken together, these findings begin to explain why young ruminants are more susceptible to infectious diseases in general, and to gastrointestinal parasites in particular, when compared to mature animals. Haematological markers of disease resistance, the prevalence of non-selected diseases and immune responses to vaccination were examined in the internal parasite-resistance flocks in Armidale NSW and the fleece rot/flystrike selection flocks at Trangie NSW. Any programme that seeks to improve resistance to parasitic or any other disease should have the capacity to make contemporary measurements of resistance to other diseases which are important in, or threaten, the production system.

Changes in T cell subpopulations of sheep due to age and dietary protein intake; association with protective immunity to Trichostrongylus colubriformis

Purified lymphocytes from peripheral blood and cannulated intestinal lymph were examined by flow cytometry, to study the effect of age, level of dietary protein, and prior exposure to helminths on their composition. This was then compared with animals resistant to Trichostrongylus colubriformis infection. When young lambs consumed a low protein diet, they developed significantly lower protective immunity to the parasite than age-matched animals offered a high protein diet, or older animals irrespective of diet. In the peripheral blood there was an increased percentage of CD4+, CD5+ and CD8+ cells with increasing age (from 8 to 51 weeks). The percent of CD4+ cells in lambs that repeatedly ingested infective larvae was significantly increased in both peripheral blood and mesenteric lymph, compared with non-immunized animals. There was a significant interaction of dietary protein and immunization, as the percentage of T19+ cells from mesenteric lymph in young lambs that consumed a high protein diet increased when they were sensitized and challenged with larvae, while this was not apparent in those that consumed a low protein diet. The increase of peripheral and local CD4+ cells may contribute to development of protective immunity to the parasite. In addition, local T19+ cell populations in young animals were influenced by the status of protein in the diet, which may in turn influence immunity.

Comparison of local and systemic responsiveness of lymphocytes in vitro to Bovicola ovis antigen and concanavalin A in B. ovis-infested and naive lambs

The in vitro proliferation assay was used to determine lymphocyte responsiveness to soluble antigen of B. ovis and to Concanavalin A (Con A) in peripheral blood, spleen and various lymph nodes from B. ovis-infested and naive lambs. From March to July, an assay of monthly blood samples showed generally higher proliferative responses to antigen and Con A in B. ovis-infested than naive lambs. The proliferative response of cells from the skin-draining prescapular lymph nodes to B. ovis antigen was significantly higher in B. ovis-infested than naive lambs. Responses of cells from the medial iliac, mediastinal and mesenteric lymph nodes (which do not receive lymph from the skin) and spleen showed no significant differences between groups. Within the B. ovis-infested lambs, the response of cells from the prescapular lymph node was significantly higher than that from any other lymphoid organ examined. Responsiveness of the prescapular, medial iliac and mesenteric lymph node and spleen cells to Con A was not significantly different between groups, while mediastinal lymph node cells showed a significantly higher response in B. ovis-infested lambs. The data indicate that the antigen-specific cellular immune response is operating mainly locally, at the level of the skin and draining lymph nodes. Responses to the T cell mitogen Con A did not support non-specific immunodepression as reported in other ectoparasite/host systems.