Measuring larval nematode contamination on cattle pastures: Comparing two herbage sampling methods

Verschave, Sien; Levecke, Bruno; Duchateau, Luc; Vercruysse, Jozef; Charlier, Johannes

doi:10.1016/j.vetpar.2015.03.031

Cited by 18 publications

(15 citation statements)

References 38 publications

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“…It has previously been observed that significant aggregation was only apparent during particular months, with the level of aggregation correlating to larval numbers (Flota-Bañuelos et al 2013 ). High PC related to low aggregation and low PC to high aggregation (Flota-Bañuelos et al 2013 ; Verschave et al 2015 ). Although mitigating factors, such as passive dispersal or fecal avoidance behaviours (Hutchings et al 2007 ) are recognized, an aggregated pasture is still expected (Grenfell et al 1995 ) and accounted for.…”

Section: Discussionmentioning

confidence: 99%

“…Calves were assumed to graze randomly across pasture. However, the spatial distribution of the larvae across the pasture was assumed to be aggregated (Boag et al 1989 ; Grenfell et al 1995 ; Verschave et al 2015 ). A negative binomial probability distribution was used with the mean being mean larval contamination of pasture (L 3 kg −1 DM) and the exponent describing the degree of aggregation k = 1·41 (Verschave et al 2015 ).…”

Section: Methodsmentioning

confidence: 99%

“…However, the spatial distribution of the larvae across the pasture was assumed to be aggregated (Boag et al 1989 ; Grenfell et al 1995 ; Verschave et al 2015 ). A negative binomial probability distribution was used with the mean being mean larval contamination of pasture (L 3 kg −1 DM) and the exponent describing the degree of aggregation k = 1·41 (Verschave et al 2015 ). Hence, the larval intake ( LI , infective L 3 larvae) of an individual calf was determined by its feed intake ( FI , kg DM) and by sampling the pasture according to the negative binomial distribution, such that: where LP t / G t (L 3 larvae day −1 ) is the mean number of L 3 larvae per ha grazed on day t .…”

Section: Methodsmentioning

confidence: 99%

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A stochastic model to investigate the effects of control strategies on calves exposed toOstertagia ostertagi

et al. 2016

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SUMMARYPredicting the effectiveness of parasite control strategies requires accounting for the responses of individual hosts and the epidemiology of parasite supra- and infra-populations. The first objective was to develop a stochastic model that predicted the parasitological interactions within a group of first season grazing calves challenged by Ostertagia ostertagi, by considering phenotypic variation amongst the calves and variation in parasite infra-population. Model behaviour was assessed using variations in parasite supra-population and calf stocking rate. The model showed the initial pasture infection level to have little impact on parasitological output traits, such as worm burdens and FEC, or overall performance of calves, whereas increasing stocking rate had a disproportionately large effect on both parasitological and performance traits. Model predictions were compared with published data taken from experiments on common control strategies, such as reducing stocking rates, the ‘dose and move’ strategy and strategic treatment with anthelmintic at specific times. Model predictions showed in most cases reasonable agreement with observations, supporting model robustness. The stochastic model developed is flexible, with the potential to predict the consequences of other nematode control strategies, such as targeted selective treatments on groups of grazing calves.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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A stochastic model to investigate the effects of control strategies on calves exposed toOstertagia ostertagi

et al. 2016

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“…A trigger of 200 eggs/g has been used previously, however this was defined for mixed infections (O'Shaughnessy et al., 2014a). Although seasonal variation in egg ratios is observed in temperate regions (Dorny et al., 1988, Vercruysse et al., 1988, Verschave et al., 2014), for simplicity it was assumed that an average proportion of 0.4 was O. ostertagi eggs (Dorny et al., 1988, Vercruysse et al., 1988, Hilderson et al., 1990, Ploeger and Kloosterman, 1993, Almería et al., 1996, Areskog et al., 2013, Verschave et al., 2015). The threshold for pepsinogen levels was assumed to be 2 IUT/l and therefore the final group involved treating calves when both FECs greater than 80 eggs/g and pepsinogen levels greater than 2 IUT/l were attained by an individual.…”

Section: Methodsmentioning

confidence: 99%

Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves

Berk

Laurenson

Forbes

et al. 2016

International Journal for Parasitology: Drugs and Drug Resistan

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The development of anthelmintic resistance by helminths can be slowed by maintaining refugia on pasture or in untreated hosts. Targeted selective treatments (TST) may achieve this through the treatment only of individuals that would benefit most from anthelmintic, according to certain criteria. However TST consequences on cattle are uncertain, mainly due to difficulties of comparison between alternative strategies. We developed a mathematical model to compare: 1) the most ‘beneficial’ indicator for treatment selection and 2) the method of selection of calves exposed to Ostertagia ostertagi, i.e. treating a fixed percentage of the population with the lowest (or highest) indicator values versus treating individuals who exceed (or are below) a given indicator threshold. The indicators evaluated were average daily gain (ADG), faecal egg counts (FEC), plasma pepsinogen, combined FEC and plasma pepsinogen, versus random selection of individuals. Treatment success was assessed in terms of benefit per R (BPR), the ratio of average benefit in weight gain to change in frequency of resistance alleles R (relative to an untreated population). The optimal indicator in terms of BPR for fixed percentages of calves treated was plasma pepsinogen and the worst ADG; in the latter case treatment was applied to some individuals who were not in need of treatment. The reverse was found when calves were treated according to threshold criteria, with ADG being the best target indicator for treatment. This was also the most beneficial strategy overall, with a significantly higher BPR value than any other strategy, but its degree of success depended on the chosen threshold of the indicator. The study shows strong support for TST, with all strategies showing improvements on calves treated selectively, compared with whole-herd treatment at 3, 8, 13 weeks post-turnout. The developed model appeared capable of assessing the consequences of other TST strategies on calf populations.

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“…Thus comprehensive systematic sampling can provide more information to estimate STH contamination across a study site, and may also be significantly more reliable than purposive sampling [43]. Verschave et al [44] compared the performance of W-route sampling with systematic unaligned sampling of sixteen 0.16 m 2 plots for estimating local levels of pasture contamination with larval nematode parasites. They found no significant difference in the mean estimate of contamination between the two methods, but noted that the systematic unaligned sampling approach required less time to complete [44].…”

Section: Spatial Sampling Regimes For Sthmentioning

confidence: 99%

Methods for Quantification of Soil-Transmitted Helminths in Environmental Media: Current Techniques and Recent Advances

Collender

Kirby

Addiss

et al. 2015

Trends in Parasitology

100

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Limiting the environmental transmission of soil-transmitted helminths (STH), which infect 1.5 billion people worldwide, will require sensitive, reliable, and cost effective methods to detect and quantify STH in the environment. We review the state of the art of STH quantification in soil, biosolids, water, produce, and vegetation with respect to four major methodological issues: environmental sampling; recovery of STH from environmental matrices; quantification of recovered STH; and viability assessment of STH ova. We conclude that methods for sampling and recovering STH require substantial advances to provide reliable measurements for STH control. Recent innovations in the use of automated image identification and developments in molecular genetic assays offer considerable promise for improving quantification and viability assessment.

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Measuring larval nematode contamination on cattle pastures: Comparing two herbage sampling methods

Cited by 18 publications

References 38 publications

A stochastic model to investigate the effects of control strategies on calves exposed toOstertagia ostertagi

A stochastic model to investigate the effects of control strategies on calves exposed toOstertagia ostertagi

Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves

Methods for Quantification of Soil-Transmitted Helminths in Environmental Media: Current Techniques and Recent Advances

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