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 CuS0₄ 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.
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