Spatial distribution on pasture of infective larvae of the gastro-intestinal nematode parasites of sheep

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

“…The use of PLC in validating nematode vaccination strategies and targeted control programmes and as input for nematode model predictions, however, requires good estimates for both low and high degrees of pasture contamination. Unfortunately, only limited data is available on the spatial distribution of trichostrongyle larvae on cattle pastures (Gruner and Sauve, 1982;Flota-Bañuelos et al, 2013), as most studies consider data collected on sheep pastures (Crofton, 1954;Tallis and Donald, 1964;Donald, 1967;Boag et al, 1989). Extrapolation of results between host species is objectionable because differences in faecal morphology (i.e.…”

“…Distribution patterns of trichostrongylid larvae on pasture are known to be aggregated (Crofton, 1954;Donald, 1967;Gruner and Sauve, 1982;Boag et al, 1989;FlotaBañuelos et al, 2013). This is to be expected, as faecal pats are not evenly distributed across pasture (MacDiarmid and Watkin, 1972;Gruner and Sauve, 1982;Hirata et al, 2011;da Silva et al, 2013) and as most L 3 do not migrate considerable distances away from the faecal pat (Gruner and Sauve, 1982;Stromberg, 1997).…”

“…These limitations do not apply to the direct quantification of L 3 on herbage. However, this technique has other important drawbacks: it is labour intensive (Boag et al, 1989;Demeler et al, 2012) and considerable variation is often seen between repeated measurements (Boag et al, 1989;Couvillion, 1993).…”

Behaviour of lambs (Ovis aries) in relation to spatial patterns of defecation on a pasture

“…Spatial heterogeneity in defecation is well known in a wide variety of habitats (Hunter, 1962;Donald & Leslie, 1969;Boag, Topham & Webster, 1989;Taylor et al, 1987); faeces accumulate in areas where sheep habitually pass the night (their`camps') (Arnold & Dudzinski, 1978) and has been quanti®ed for adult merino sheep (Taylor et al, 1987). However, no information on frequency of defecation of sheep seems to have been published since Arnold & Dudzinski (1978) reported that such data were not available.…”

Compound processes as models for clumped parasite data

“…To analyze such aggregated parasite data, the fitting of the negative binomial distribution is a common method, as in [4] to model the abundance of the fluke Diplostomum spathaceum in fish, in [5] for European red mite on apple leaves, in [6] for the tapeworms Echinococcus granulosus and multilocularis in dogs, in [7] for the nematode Trichinella spiralis in rabbits and in [8] for the larval stage of the mites Allothrombium pulvinum Ewing in lice. However, these models do not take into account the age of the hosts, which is known to influence the parasite pattern [9,10,11]. To incorporate age, negative binomial regression can be used, as in modeling the age-dependent frequency of the nematode Wuchereria bancrofti in humans [12], or of the nematodes Ostertagia gruehneri and Marshallagia marshalli in reindeer [13].…”