Methods of infesting sheep with gastro-intestinal nematodes after cryopreservation: dosing of larvae in gelatin capsules compared to dosing of larvae in water suspension.

Cryopreservation of the infective larvae (L3) of nematodes is being used increasingly for the routine maintenance of pure strains of nematodes in the laboratory. Gelatin capsules are frequently used to administer the L3 of nematodes to sheep, but with some nematode species this method usually does not give good results with cryopreserved larvae. The development in sheep of cryopreserved L3 of Trichostrongylus spp. and other ovine nematodes was compared when the larvae were administered either in a suspension or in gelatin capsules with or without the use of CuSO4 to stimulate the oesophageal groove reflex. Significantly larger numbers of cryopreserved L3 developed when dosed per os in suspension than when the L3 were dosed in gelatin capsules. Stimulation of the oesophageal groove did not appear to affect the numbers of worms that developed from L3 dosed in suspension. It is speculated that L3 in suspension bypass the rumen to go directly into the abomasum, while those in gelatin capsules enter the rumen, thus closely approximating the natural infestation of grazing ruminants. In these trials, however, only cryopreserved L3 were used. Sufficient numbers of cryopreserved L3 of Trichostrongylus falculatus and T. colubriformis in suspension developed, so that it seems unlikely that laparotomy will be required for routine infestations in the laboratory.