No abstract

Three years after the start of an experiment to assess the merits of thiabendazole (TBZ) treatment of trichostrongylid parasites in weaner sheep, field isolates of Ostertagia spp and Trichostrongylus spp were made from weaner sheep treated under one of three treatment schemes. Treatment frequencies were "nil", "planned" (5 or 6/year) and "regular" (every 3 weeks). In addition an isolate was taken from a group of "tracer" sheep drenched with TBZ every 10 days. Resistance to TBZ was assessed using an in vitro egg hatch assay, pre- and post-treatment faecal egg counts and a controlled anthelmintic efficiency test. Pre- and post-treatment egg counts revealed the presence of TBZ-resistance in field isolates of mixed species. Egg hatch assays indicated a level of resistance for Ostertagia spp which was proportional to the frequency of TBZ treatment. The "planned", "regular" and "tracer" strains of Ostertagia spp had resistance ratios for eggs of 4, 13 and 15 respectively when compared to the "nil" strain. In the anthelmintic efficiency assay treatment with 44 mg kg-1 and 88 mg kg-1 of TBZ removed 82 and 96% respectively of the total Ostertagia burden (adults and larvae) from the "nil" strain and 30 and 75% respectively from the "planned" strain. The same dose rates against the "regular" and "tracer" strains and additional rates of 132 or 176 mg kg-1 against the "tracer" strain failed to reduce the Ostertagia burden significantly. Intestinal Trichostrongylus spp from all isolates were fully susceptible to TBZ at 44 mg kg-1. Levamisole at 7.0 mg kg-1 was highly effective (99% reduction) against the "tracer" strain of Ostertagia.

1. Sixty-four Dorset Horn ewes and sixty Half- Bred ewes were X-rayed in the pelvic region at stages of pregnancy between 51 and 110 days.2. Diagnosis of pregnancy and estimates of the number of foetuses carried were made from the X-ray film.3. Over the range of gestation stages examined, interpretation of the number of foetuses present was found to be most accurate at stages between 91 and 110 days.4. An accurate estimation of whether the ewe is pregnant or barren can be made from 50 days onwards.

1. The literature on the early weaning of lambs has been reviewed.2. Four experiments were carried out at the Grassland Research Institute, Hurley, during 1959, 1960 and 1961 on the early weaning of Suffolk x Half-Bred lambs. The technique used involved weaning one of a pair of twin lambs at ages varying from 15 to 28 days.3. In 1959 oneof each of apair of six twin lambs was weaned on to grass alone at 15–20 days. No losses occurred, but the weaned lambs grew very slowly. The unweaned twin lambs remaining with the ewes (i.e. reared as singles) grew at rates comparable to those of single lambs.

1. Observations carried out on four groups of sheep during the spring of 1954 are described.2. A spring-rise in the worm-egg output was found to occur in all the groups studied.3. The management of the animals precluded rcinfestation during the spring and, in two instances, from 8th January and 22nd, respectively.4. Time of lambing and nutritional level appeared to influence the onset and magnitude of the spring increase.