Assessment of targeted selective treatment criteria to control subclinical gastrointestinal nematode infections on sheep farms.

Control of sheep gastrointestinal nematode (GIN) infections mostly relies on the use of anthelmintics. Refugia-based control strategies as targeted selective treatments (TST) can delay anthelmintic resistance development, but the optimal decision criteria for selecting individuals to be treated in subclinical infection scenarios remain unclear. The present study aimed to evaluate the suitability of body condition score (BCS) and faecal egg counts (FEC) as treatment indicators and to determine their optimized threshold values for treatment in TST by determining the relationships of BCS, FEC and anthelmintic treatment with several productive parameters in pre-mating and pre-partum periods at an individual level. Deworming in pre-mating period increased BCS gain, but its magnitude was directly associated with strongyle FEC before treatment. Deworming also increased fertility in ewes with BCS < 2.75 and the proportion of lambing ewes that got pregnant during the first ovulation cycle. Nevertheless, treatment did not yield productive benefits in ewes with higher BCS values. On the other hand, deworming in the pre-partum lowered lamb peri-partum mortality and increased lamb weight at birth and the growth of lambs during lactation, especially in lambs born from ewes with strongyle FEC > 400 epg before treatment. These results showed that FEC and especially BCS can be potential decision criteria for the implementation of TST in these types of scenarios. The TST scheme derived from the present results on the control of GIN infections should include anthelmintic treatment of ewes with BCS lower than ≈ 3 approximately five weeks before mating and lambing. In the pre-lambing period, treatment may be unnecessary if flock mean strongyle FEC is lower than ≈ 200 epg, as the proportion of ewes with individual FEC > 400 epg would be very low. The results suggest that implementation of this TST scheme would provide benefits, such as the improvement of productivity, a rational management of parasites in refugia, and preservation of future efficacy of anthelmintics, in comparison to traditional deworming schemes.

Improving the detection of anthelmintic resistance: evaluation of faecal egg count reduction test procedures suitable for farm routines.

The faecal egg count reduction test (FECRT) is the main method of detection of anthelmintic resistance (AR) in nematodes of veterinary importance. However, although the FECRT is standardised, the diagnostic performance of this method has not been fully characterised. In this survey Monte Carlo routines were used to simulate the estimation of faecal egg count reduction (FECR) with several FECRT protocols that were performed under different field and laboratory conditions. The goal was to determine, from a practical viewpoint, the most suitable protocols for farm routines and to evaluate the diagnostic performance of FECRTs across different parasitological scenarios with several levels of AR. The simulated field procedures included variations in the sample size and the sampling (or not) of a control group, whereas the simulated laboratory procedures comprised group mean individual-based vs. composite-based FECR estimations and variations in the egg detection threshold of the McMaster technique. For composite procedures, the random weight variations among individual samples and an increased number of McMaster chamber counts were also simulated. The results showed that FECRTs were moderately affected by inaccuracy but crucially affected by imprecision, and both parameters were clearly dependent on the parasitological conditions and the laboratory and field procedures used. An individual-based FECRT method performed without a control group was the most appropriate to quantify the AR, whereas a composite-based method with a control group was the easiest method for discriminating susceptible and resistant parasite populations. More interestingly, the diagnostic performance of the simulated FECRT methods was low for the procedures that are currently recommended by the World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) and for many of the typical field and laboratory procedures that are currently implemented. Therefore, the results suggest that the diagnostic performance of the FECRT should be re-evaluated, and the recommendations of the W.A.A.V.P. should be redefined. Finally, theoretic critical conditions for FECRT procedures have been defined to improve future AR surveys and to allow the interpretation of FECRT results with the necessary caution according to the diagnostic performance expected for every FECRT procedure and parasitological scenario.

Effect of nematophagous fungus Duddingtonia flagrans and energy supplementation on the epidemiology of naturally infected kids.

Gastrointestinal (GI) nematode infection is a major constraint for grazing livestock production. The increasing prevalence and severity of anthelmintic-resistant nematodes in many parts of the world has led to a search for non-chemical control options. Under experimental conditions, the nematophagous fungus Duddingtonia flagrans is emerging as an alternative to chemotherapy for the control of GI nematode infection in biological production systems. Also, recent information points to the role of energy nutrition to increase the immune response against GI nematode infection. In this study the effect of D. flagrans and energy supplementation on the epidemiology of GI nematode infections is explored on grazing kids. Four groups of 10, 4-month old goats were turned out on infected pasture in the early spring and allocated to four separate paddocks where they were rotationally grazed for 16 weeks. One of these groups (F) received 0.5 x 10(6) D. flagrans spores/kg BW/d. Another group (S) was supplemented with 100 g barley grain per day. A third group (F+S) received both nematophagous fungi and barley supplement treatments simultaneously while the fourth group (C) was used as a non-treated control. Both nematophagous fungi and barley supplement had a significant effect (P<0.01) on reducing pasture infectivity, faecal egg excretion and worm burdens at slaughter that was particularly evident for Trichostrongylus colubriformis. The combination of both treatments showed a synergistic effect on the control of gastrointestinal nematode infections. At slaughter, the average total post-mortem worm count of the F+S group was reduced by 65% compared with the non-treated control. The results herein show that D. flagrans can act as an efficient biological control agent against kid GI nematode infections on pasture, which could further improve carcass characteristics. While small amounts of energy supplement can also reduce kid infection, the effect of D. flagrans as a biological control agent appeared clearly enhanced both in magnitude and duration by energy supplementation. This has clear implications for grazing animals and provides an efficient method for the practical control of parasitic nematodes in biological production systems.