The host immune response to gastrointestinal nematode infection in sheep

non peer reviewedGastrointestinal nematode infection represents a major threat to the health, welfare and productivity of sheep populations worldwide. Infected lambs have a reduced ability to absorb nutrients from the gastrointestinal tract, resulting in morbidity and occasional mortality. The current chemo-dominant approach to nematode control is considered unsustainable due to the increasing incidence of anthelmintic resistance. In addition there is growing consumer demand for food products from animals not subjected to chemical treatment. Future mechanisms of nematode control must rely on alternative, sustainable strategies such as vaccination or selective breeding of resistant animals. Such strategies take advantage of the host's natural immune response to nematodes. The ability to resist gastrointestinal nematode infection is considered to be dependent on the development of a protective acquired immune response; although the precise immune mechanisms involved in initiating this process remain to be fully elucidated. In this paper current knowledge on the innate and acquired host immune response to gastrointestinal nematode infection in sheep and the development of immunity is reviewed.We gratefully acknowledge funding support for the research in our laboratories from the Teagasc Walsh Fellowship Programme, the Allan and Grace Kay Overseas Scholarship and the EC-funded FP7 Programme. We also thank the BBSRC Animal Health Research Club for funding part of this research (grant BB/l004070/1

Worm Control for Small Ruminants in Tropical Asia

Livestock Production/Industries,

Problems in the control of nematode parasites of small ruminants in Malaysia

Nematode parasitic disease, attributed mainly Haemonchus contortus, is the greatest disease problem of small ruminants in Malaysia. This thesis comprises 6 studies on the emergence of anthelmintic resistance in these parasites, and how control may be managed by exploiting the nematophagous fungus Duddingtonia flagrans. A survey of the prevalence of anthelmintic resistance (AR) on Peninsular Malaysia revealed 50% of the sheep (n=39) and 75 % of the goat farms (n=9) were infected with nematode parasites that were resistant to the benzimidazoles. Resistance to levamisole, closantel and ivermectin was also detected. Another study on a government sheep breeding farm, showed multiple AR involving the benzimidazoles, levamisole and ivermectin (plus suspect moxidectin resistance). Continuing these investigations to eastern Malaysia, showed anthelmintic failure to all the broad-spectrum groups on all the government small ruminant breeding farms. New approaches to worm control were urgently required. Studies on the potential of biological control by the use of nematophagous fungi against the free-living stages on pasture, were carried out to assess its suitability and efficacy for use in the tropical environment that is typical for Malaysia. In a survey for the presence of nematode trapping fungi from faecal samples of livestock, several nematophagous species including D. flagrans and Arthrobotrys oligospora were identified. Mass production of D. flagrans spores on various local media was attempted, and the product was also tested in pen trials where sheep were fed the spores at different dose rates, either as a supplement, or in feed blocks. Daily fungal feeding by both means resulted in an 80-95% reduction in infective larvae in faecal cultures. Similar results were found in small scale grazing experiments, where sheep were fed daily with fungal spores for 3 consecutive months. Pen trials comparing goats and sheep, showed no difference between the two livestock species. Larger scale field trials where D. flagrans was combined with rapid rotational grazing, showed excellent parasite control. This indicates that the integration of biological control with measures such as rotational grazing provides viable options for sustainable production of small ruminants in the tropics, where AR is becoming a major threat to livestock production

Worm control for small ruminants in tropical Asia

ACIAR funded a collaborative project between research organisations in Southeast Asia for ILRI and regional partners to explore new ways to control helminth parasites in the tropics. The project aimed to increase small ruminant production in Southeast Asia by controlling internal parasites, which are one of the major constraints to sheep and goat production in the tropics. Control of internal parasites also provides an avenue for general improvement in husbandry methods. The three objectives of the project are: to prevent the spread of resistance to anthelmintics (dewormers) used for control of nematode parasites of sheep and goats in Asia; to assess genetic variation in resistance to gastrointestinal nematode parasites in different breeds of sheep and goats; and to disseminate information about control of internal parasites in the tropics. This publication and the accompanying CD draw together information from a number of sources to describe the state of research and development on worm control in sheep and goats in Asia and the Pacific. Topics of discussion include worm control; economic impacts of worm control; integrated approaches to sustainable parasite control; anthelmintic resistance; appropriate breeds and breeding schemes; options to overcome worm infection; impact of parasitism on the development of small ruminant populations; worm control methods; improving small ruminant productivity; and prevalence of internal parasites

Tannin containing legumes as a model for nutraceuticals against digestive parasites in livestock

Parasitic infections with gastrointestinal nematodes (GINs) still represent a worldwide major pathological threat associated with the outdoor production of various livestock species. Because of the widespread resistance to synthetic chemical anthelmintics, there is a strong impetus to explore novel approaches for a more integrated management of the infections. The use of nutraceuticals in the control of GINs is one of the alternatives which has been widely studied for since 20 years. The objectives of this review are: i) to define and illustrate the concept of ‘nutraceutical’ in the context of veterinary parasitology based on data obtained on the most studied GIN models in small ruminants, the tannin-containing legumes (Fabaceae); ii) to illustrate how the ‘nutraceutical concept’ could be expanded to other plants, other livestock production systems and other GI parasitic diseases, and iii) to explain how this concept is opening up new research fields for better understanding the interactions between the host, the digestive parasites and the environment

Animal Behaviour Packs a Punch: From Parasitism to Production, Pollution and Prevention in Grazing Livestock

Behaviour is often the fundamental driver of disease transmission, where behaviours of individuals can be seen to scale up to epidemiological patterns seen at the population level. Here we focus on animal behaviour, and its role in parasite transmission to track its knock-on consequences for parasitism, production and pollution. Livestock face a nutrition versus parasitism trade-off in grazing environments where faeces creates both a nutritional benefit, fertilizing the surrounding sward, but also a parasite risk from infective nematode larvae contaminating the sward. The grazing decisions of ruminants depend on the perceived costs and benefits of the trade-off, which depend on the variations in both environmental (e.g., amounts of faeces) and animal factors (e.g., physiological state). Such grazing decisions determine the intake of both nutrients and parasites, affecting livestock growth rates and production efficiency. This impacts on the greenhouse gas costs of ruminant livestock production via two main mechanisms: (1) slower growth results in longer durations on-farm and (2) parasitised animals produce more methane per unit food intake. However, the sensitivity of behaviour to host parasite state offers opportunities for early detection of parasitism and control. Remote monitoring technology such as accelerometers can detect parasite-induced sickness behaviours soon after exposure, before impacts on growth, and thus may be used for targeting individuals for early treatment. We conclude that livestock host x parasite interactions are at the centre of the global challenges of food security and climate change, and that understanding livestock behaviour can contribute to solving both

Breeding for Resistance to Infectious Diseases in Small Ruminants

Livestock Production/Industries,

Animal Behaviour Packs a Punch: From Parasitism to Production, Pollution and Prevention in Grazing Livestock

Behaviour is often the fundamental driver of disease transmission, where behaviours of individuals can be seen to scale up to epidemiological patterns seen at the population level. Here we focus on animal behaviour, and its role in parasite transmission to track its knock-on consequences for parasitism, production and pollution. Livestock face a nutrition versus parasitism trade-off in grazing environments where faeces creates both a nutritional benefit, fertilizing the surrounding sward, but also a parasite risk from infective nematode larvae contaminating the sward. The grazing decisions of ruminants depend on the perceived costs and benefits of the trade-off, which depend on the variations in both environmental (e.g., amounts of faeces) and animal factors (e.g., physiological state). Such grazing decisions determine the intake of both nutrients and parasites, affecting livestock growth rates and production efficiency. This impacts on the greenhouse gas costs of ruminant livestock production via two main mechanisms: (1) slower growth results in longer durations on-farm and (2) parasitised animals produce more methane per unit food intake. However, the sensitivity of behaviour to host parasite state offers opportunities for early detection of parasitism and control. Remote monitoring technology such as accelerometers can detect parasite-induced sickness behaviours soon after exposure, before impacts on growth, and thus may be used for targeting individuals for early treatment. We conclude that livestock host x parasite interactions are at the centre of the global challenges of food security and climate change, and that understanding livestock behaviour can contribute to solving both

Interactive effects between genotype, protein nutrition and immune status on the parasite-induced anorexia of sheep

Infection with nematode parasites detrimentally affects production efficiency in grazing animals, mainly through a reduction in food intake (anorexia).This thesis describes a series of six in vivo experiments designed to investigate the interactive effects of genotype, immune status and protein nutrition on the occurrence of parasite-induced anorexia of sheep. The experiments also investigated the role of the hormore leptin in immune response and anorexia following infection with gastrointestinal nematodes. In general, each experiment involved two breeds of lambs (Suffolk x Greyface, S, and Scottish Blackface, B) or ewes (Greyface cross, G, and Scottish Blackface, B) that are known to differ in their production potential. In each experiment, animals were either infected with the abomasal nematode Teladorsagia circumcincta and fed ad libitum or non-infected and fed either ad libitum or restrictedly..The first two experiments investigated the effect of a primary and a secondary infection on anorexia and plasma leptin concentrations (PLC) in growing lambs (Chapter 3). The secondary infection started two weeks after the discontinuation of the primary infection. The results showed that lambs of the S breed were more susceptible to nematode infection than B lambs, as judged from the differences in faecal egg counts. Primary infection resulted in anorexia in S lambs but not in B lambs and re-infection tended to affect the food intake of S lambs only. Infection did not result in an acute increase in PLC, but its effect was significant when variation in food intake between treatments was accounted for. These results suggest that anorexia can occur in previously infected lambs, thus the effect of re-infection on anorexia was further investigated (Chapter 4).Chapter 4 describes a series of 3 experiments with lambs. In these experiments, previously naïve lambs of approximately 3 (experiment I) or 7 (experiment II) months of age were infected with T. circumcincta for either 10 or 7 weeks, respectively. Lambs of experiment I were re-infected either 4 or 8 weeks after the end of the primary infection (experiment III). The results showed that the breed differences in resistance to infection were not associated with breed differenced in the degree of anorexia (experiment I) and infection of 7-month old lambs did not result in anorexia. Re-infection of previously infected lambs did also not result in anorexia when lambs were re-infected 4 or 8 weeks after the end of the primary infection. In addition, the results of these experiments showed that nematode (re)infection did not result in an increase of PLC. These results suggest that leptin may be involved in the response of Iambs to infection, but it is unlikely that leptin alone is responsible for the parasite induced anorexia in lambsThe last experiment (Chapter 5) investigated the consequences of protein supplementation on anorexia, and PLC in infected periparturient ewes. Infection resulted in a breakdown of immunity to parasites (PPRI) and a reduction in food intake in both breeds. The breeds differed in the extent of PPRI (G ewes having higher FEC than B ewes), but not in the magnitude of anorexia. Protein supplementation resulted in a reduction in FEC, but had no effect on the magnitude of anorexia. Plasma leptin concentrations changed significantly over time, but were not affected by protein supplementation or infection. It was concluded that infection with T. circumcincta in periparturient ewes results in anorexia that is not alleviated by protein supplementation. Leptin is unlikely to be responsible for the anorexia of nematode infection in periparturient ewes.The outcomes of the above experiments are brought together with the literature in the General Discussion (Chapter 6) and directions of future work, to elucidate the mechanisms as well as the functional significance of anorexia, are put forward

Influence of nutrition on parasitism in periparturient dairy ewes

Influence of Nutrition on Parasitism in Periparturient Dairy Ewes Increased anthelmintic resistance has lead many researchers to investigate alternative methods of parasite control. It is believed that most larval contamination of the pasture is derived mainly from the mature breeding ewe due to the periparturient rise (PPR) in faecal egg counts (FECs). The aim of this study was to determine if manipulating the dietary supply of metabolisable protein (MP) or fish oil to the periparturient ewe can moderate the PPR. The first experiment investigated the effects of increased MP supply and fish oil on the PPR of machine-milked ewes. The second experiment investigated the effects of nematode infection and increased MP supply on the PPR of machine-milked ewes and the third experiment investigated the effects of machine milking compared to suckling twin lambs and the effect of increasing dietary MP on the PPR. In all the experiments, FECs, peripheral eosinophil counts, blood haematology and metabolite analyses were carried out and milk yields and composition were recorded. Additionally, in Exp.l immunoglobulin titres were determined, in Exp.2 pepsinogen assays were carried out and in Exp.3 blood was collected for lymphocyte stimulation responses. In Exps.2 and 3, the ewes were slaughtered to investigate nematode burden, mucosal mast cell (MMC) and mucosal eosinophil counts. The dietary treatments had no significant effects on the immunological parameters throughout all three experiments, although in Exp.2 larval challenge increased MMCs, mucosal eosinophils and pepsinogen assays. There was no benefit of increased dietary MP or fish oil on FECs in Exp.l. and no beneficial effect of increased dietary MP on FECs during Exp.2. However, in Exp.3 increased MP reduced the FECs from the twin suckled ewes but had no effect on the machine-milked ewe FECs. The machine-milked ewes had significantly lower milk yields than the suckled ewes and it may be that the machine-milked dairy ewe may not suffer the PPR due to some unidentified mechanism