[Cross fertilization of Teladorsagia trifurcata with T. circumcincta]

Species and morphs in the Ostertagiinae: an allozyme study of seven species

Five enzymes, malate dehydrogenase, lactate dehydrogenase, mannose-phosphate isomerase, glucose-phosphate isomerase and phosphoglucomutase from seven putative species of Ostertagiinae were compared using starch-gel electrophoresis. The Nei distances were not much affected by origin of specimens or host species. Six of the putative species could form polymorphic pairs: Ostertagia ostertagi and Ostertagia lyrata, Ostertagia leptospicularis and Ostertagia kolchida, Teladorsagia circumcincta and Teladorsagia trifurcata. The Nei distance was of the same magnitude (> 0.6) between species pairs, O. ostertagi, O. leptospicularis, T. circumcincta and Spiculopteragia spp.

A method for studying interbreeding of nematodes of the subfamily Ostertagiinae in sheep with abomasal fistulae

Interbreeding in two nematode species, Teladorsagia circumcincta and Ostertagia leptospicularis, was studied in lambs using small populations. Offspring from a single mated female were investigated for T. circumcincta. The following protocol was found to be satisfactory for small populations: virgin females and adult males were obtained from donor lambs infected artificially and transferred into the abomasa of fistulated sheep or lambs being treated with a long-acting corticosteroid. Infective larvae obtained from cultures of faeces of fistulated sheep were given to a recipient lamb and when this animal was slaughtered it was possible to examine the adult nematodes resulting from the interbreeding. Interbreeding between one male and one female was not successful while there was limited recovery of infective larvae from the implantation of a single mated female.

Summer-arrested development of abomasal trichostrongylids in Awassi sheep in semi-arid areas of north-west Syria

Inhibition in trichostrongylids was studied in Awassi sheep in North-west Syria, which has cold winters and hot summers. On six occasions during a 1-year period, five ewes with natural helminth infections were slaughtered after being held in pens for 3 weeks. The percentage of inhibited larvae was lowest in January (6%); it increased during the spring to 76.7% in April and to 84.6% in June and then decreased during the autumn (57.1% in September, 26.1% in December). Inhibition occurred mainly during the early fourth stage in mucosa but was also observed during the late fourth stage in digesta. Teladorsagia circumcincta was the main species involved, but it seemed that this phenomenon also occurred in Marshallagia marshalli.

Apparent absence of genetic differences among species of Teladorsagia (Nematoda: Trichostrongylidae)

The technique of allozyme electrophoresis was applied to three species of Teladorsagia present in sheep to determine the extent of genetic variation among species. Thirty-four enzyme loci were established of which 22 were invariant and 12 were shown to be polymorphic. No fixed allelic differences were detected among the species and the level of polymorphism was within the range found commonly between populations of a single species. Therefore, the genetic data support breeding data and existing morphological evidence that T. circumcincta, T. davtiani and T. trifurcata as currently recognized do in fact belong to a single species.