Immune markers in goats selected for reduced gastrointestinal nematode egg count under artificial infection conditions.

This study aimed to further investigate the mechanisms responsible for inhibition of gastrointestinal nematode egg production in a line of Scottish Cashmere Goat selected for low faecal egg count. Animals were chosen as the lowest egg producers from a line selected for low egg output (selected group) with a second group from the wider herd based on high faecal egg count as controls. All animals were artificially infected with Teladorsagia circumcincta and Trichostrongylus vitrinus, then treated with anthelmintic and challenge infected prior to euthanasia and post mortem sampling. There was no effect on body weight between groups at any point in the study. Mean faecal egg count was reduced by 68 % in the selected group when compared with the controls. Circulating eosinophil counts were consistently elevated in the selected group, but this was only marginally significant (P = 0.045). Most of the circulating and tissue antibodies (IgG, IgA and IgE) measured were slightly elevated in the selected group but not significantly. Mucosal mast cells, eosinophils and globule leukocyte levels were higher in the abomasal and intestinal tissues in selected animals. Following challenge infection there was no difference in numbers of parasites, however there were more early stage parasite larvae and fewer late stage larvae in the both the abomasum and duodenum of the selected group compared with the unselected group, indicating some inhibition of parasite development. Overall, the study further demonstrated that selection based on low egg count has resulted in a line of goats producing significantly fewer parasites under identical infection with no effect on bodyweight. This appears to be associated with elevation in antibody and effector cells. Some evidence of host inhibition of parasite development was observed in the selected animals.

Helminth parasites are associated with reduced survival probability in young red deer.

Helminths are common parasites of wild ungulates that can have substantial costs for growth, mortality and reproduction. Whilst these costs are relatively well documented for mature animals, knowledge of helminths' impacts on juveniles is more limited. Identifying these effects is important because young individuals are often heavily infected, and juvenile mortality is a key process regulating wild populations. Here, we investigated associations between helminth infection and overwinter survival in juvenile wild red deer (Cervus elaphus) on the Isle of Rum, Scotland. We collected fecal samples non-invasively from known individuals and used them to count propagules of 3 helminth taxa (strongyle nematodes, Fasciola hepatica and Elaphostrongylus cervi). Using generalized linear models, we investigated associations between parasite counts and overwinter survival for calves and yearlings. Strongyles were associated with reduced survival in both age classes, and F. hepatica was associated with reduced survival in yearlings, whilst E. cervi infection showed no association with survival in either age class. This study provides observational evidence for fitness costs of helminth infection in juveniles of a wild mammal, and suggests that these parasites could play a role in regulating population dynamics.

Integrating applied parasitological and molecular epidemiological methodologies to investigate the capacity of Haemonchus contortus to over-winter on pasture in Scotland.

BACKGROUND: The Barber's Pole worm, Haemonchus contortus is of major concern to sheep producers, particularly in the southern hemisphere. This nematode is also commonly found in many sheep flocks in Northern hemisphere countries but is generally not associated with acute clinical pathology. As with other nematode species, the pattern of disease is changing in the United Kingdom. Changes in management practices, climate, anthelmintic resistance prevalence and parasite adaptation are possible factors thought to be responsible for this. METHODS: In the present study, a combination of traditional applied parasitological and molecular species identification techniques were used to assess the capability of H. contortus infective larvae to over-winter on pasture and infect lambs in early spring. RESULTS: Adult and inhibited H. contortus worms were identified in previously worm-free tracer lambs that had grazed contaminated pasture in late winter/early spring (February/March). CONCLUSION: The study illustrated the benefit of using classical applied parasitology techniques in conjunction with molecular species identification methods to explore the epidemiology of gastro-intestinal nematodes of livestock. This study also demonstrated that larvae were able to survive over-winter, albeit in small numbers, and potentially contaminate pastures earlier than previously considered in northern regions of the UK.

Faecal egg counts and immune markers in a line of Scottish Cashmere goats selected for resistance to gastrointestinal nematode parasite infection.

This study aimed to investigate the effect of selection for low faecal egg count (FEC) in Scottish Cashmere goats in comparison to a control line of unselected goats grazing the same pasture. Goats from generations F2 through to F9 were monitored for FEC, bodyweight, peripheral eosinophilia and IgG, IgA and IgE response against Teladorsagia circumcincta from the end of their first grazing season, through winter housing (during which a single artificial challenge dose of 10,000 drug susceptible T. circumcincta was given) and the following full grazing season. The study demonstrated that selected line animals excreted a significantly lower number of parasite eggs (P<0.01) in the majority of generations examined. Liveweight productivity was unaffected by selection. Although selected line animals had greater numbers of circulating eosinophils in many of the generations (four generations of males and six generations of females, P<0.05), there was no direct link between eosinophilia and reduced FEC. Immunoglobulin levels showed no consistent difference between selected and control lines. IgG, IgA and IgE levels were not different between lines over the whole dataset (P>0.05), although the selected line had significantly elevated or reduced levels (P<0.05) for all three within individual generations. There were significant associations between increased IgG and reduced FEC under artificial infection conditions (P=0.02). Increased IgA was also significantly associated with elevated FEC during the second grazing season (P<0.001). The study demonstrates that selection produced a line of goats with consistently reduced FEC compared with control animals, but did not identify a clear relationship between any of the immune markers measured and faecal egg output.

Effect of anthelmintic treatment strategy on strongylid nematode species composition in grazing lambs in Scotland.

BACKGROUND: Refugia based anthelmintic protocols aim to reduce the rate of development of anthelmintic resistance in gastrointestinal nematodes (GIN). Previous studies have illustrated the impact of different drenching regimes on drug efficacy and animal growth; however, the impact on nematode populations has yet to be characterised within natural infections. This study investigated the changes in species composition of GIN throughout the grazing season, following implementation of four different ivermectin drenching regimes over six years: neo-suppressive monthly treatment (NST), targeted selective treatment (TST), strategic prophylactic treatment (SPT) and treatment upon observation of clinical signs (MT). METHODS: Lambs were grazed on one of eight replicate paddocks each grazing season following treatment regimes assigned in year 1. Faecal samples were collected fortnightly from all animals and hatched to first stage larvae (L1). DNA was extracted from individual L1 and a multiplex PCR assay targeting the internal transcribed spacer 2 (ITS2) region of Teladorsagia circumcincta, Trichostrongylus spp. and Haemonchus contortus conducted. Other species were identified using species-specific PCR. Worm-naïve tracer lambs were grazed on the paddocks at the start and end of each grazing season and adult worms recovered at post mortem to investigate the parasite population on pasture. RESULTS: Results showed an overall decrease in species diversity in egg output from the NST group which occurred within a single grazing season and was consistent throughout the experiment. Species diversity was protected over six years in groups implementing TST, SPT and MT treatment regimes, designed to offer refugia. The expected shift in species prevalence throughout the season from Teladorsagia to Trichostrongylus was observed in all but the NST group where only Teladorsagia spp. were recovered from trial lambs by the end of the experiment. Worm burdens indicated the presence of several species at relatively low abundance on pasture in the NST group in 2011. However, these species were not represented in egg output from trial lambs, probably due to the frequent anthelmintic treatment administered throughout the grazing season. CONCLUSION: The molecular methods utilised here worked well. The comparable results of the three refugia-based treatment regimes suggest that nematode diversity can be maintained using part or whole group treatments if a rich supra-population of parasites are available to re-infect animals post treatment.

Viability of the Happy Factor™ targeted selective treatment approach on several sheep farms in Scotland.

The aim of this study was to examine the use of Happy Factor™ weight based targeted selective treatment (TST) on several commercial farms in Scotland in combination with findings from a long term trial on a research farm to assess the potential for TST use in varying farming operations as an alternative to the current regimen of whole flock treatment. Lambs on each farm were regularly weighed and climatic conditions and pasture availability measured for inclusion into the Happy Factor™ model to calculate weight targets. Half of the lambs were allocated to TST treatment and any failing to reach the weight target was treated with the anthelmintic of choice on that farm, while the remaining half of each flock was treated with anthelmintic as per normal practice on that farm (routine treatment, RT). The research farm (farm 1) hosted a long term trial using four anthelmintic treatment regimes over 6 years, and data from two regimes are presented here, alongside findings from three further farms: two commercial enterprises (farms 2 and 3) and a research farm operating as a commercial analogue with two breeds (farms 4a and 4b). The effect of TST strategy on lamb productivity and the number of anthelmintic treatments was investigated. There was no evidence (p>0.300) that mean bodyweight or growth rate was different between TST and RT groups on any of the farms and 95% confidence intervals of TST and RT groups generally suggested that TST had negligible unfavourable effects on the average growth of lambs for most of the farms. Growth rates ranged from 97.39 to 189.16g/day reflecting the varied nature of the farms. All commercial farms used significantly less (1.34 RT versus 1.14 TST treatments per animal, p<0.05) anthelmintic in lambs following TST, with a reduction from 1, 1, 1.03 and 1.14 to 0.77, 0.57, 0.82 and 0.81 in the number of treatments per animal for farms 2, 3, 4a and 4b respectively. This study suggests that TST is a viable means of controlling parasitic disease without incurring production losses.

A comparative study of the effects of four treatment regimes on ivermectin efficacy, body weight and pasture contamination in lambs naturally infected with gastrointestinal nematodes in Scotland.

Refugia-based drenching regimes have been widely recommended to slow development of anthelmintic resistance but there are few comparisons between different treatment approaches in the UK. The impact of four ivermectin treatment regimes on drug efficacy, lamb body weight and nematode contamination during a 154 day grazing season were evaluated in a consecutive five year field study. Regimes were whole-flock treatment every 4 weeks (NST), targeted selective treatment (TST) based on individual performance, strategic whole-flock treatments at pre-determined times (SPT) or whole-flock treatment when clinical signs were apparent (MT). Mean numbers of ivermectin drenches administered per season were 4.0, 1.8, 2.0 and 1.4 for NST, TST, SPT and MT groups, respectively. The mean anthelmintic efficacy (AE) for each treatment group was based on faecal egg count reduction post-treatment employing a bootstrap sampling based algorithm. Mean AE was 95-98% for all groups in 2006 and mean AE (95% confidence limits) for NST declined to 62% (55%, 68%) in 2010. In comparison, AE for TST, SPT and MT in 2010 were 86% (81%, 92%), 86% (83%, 90%) and 83% (78%, 88%), respectively. Body weight in TST and SPT was similar to NST in all years (p > 0.05), however MT lambs were lighter than NST in 2006-2008 (p â©½ 0.04). Tracer lamb worm burdens was lowest in NST but was not significantly different between other groups. Overall, both the TST and SPT regimes appeared to maintain animal performance and conserve anthelmintic efficacy compared with a neo-suppressive anthelmintic treatment regime.