Interspecific interactions in naturally acquired nematode communities from sheep abomasum in relation to age of host and season in four areas of León (Spain).

The abomasa of naturally infected ewes (407) and lambs (190) from four areas of León were collected weekly over 2 years in the abattoir of León (north-west Spain). The major species and morphs found were Teladorsagia circumcincta and Trichostrongylus axei and to a lesser extent Marshallagia marshalli and Teladorsagia trifurcata. The putative interactions between species were assessed by Euclidian distances based on the results of multivariate analyses. The estimation of interaction was either based on mean intensities of worm burdens or on frequencies of nematode species within individual hosts. The areas, years, seasons and categories of sheep (ewes or lambs) did not influence the interaction estimates. These were not dependent upon the size of worm burden. The majority of interactions were positive. Slight negative interactions were found only with T. circumcincta-T. axei, T. circumcincta-M. marshalli and M. marshalli-T. axei. Positive interactions were recorded between the less frequent species.