Brief Communication - Susceptibility of the breeding ewe to
parasitism
R.W. McAnulty, A.S. Familton, A.R. Sykes
Animal and Veterinary Sciences Group, Lincoln University,
Canterbury, New Zealand
Pregnant Coopworth ewes were allocated to four periods of
parasitic challenge which commenced either -4, 0, 6 or 12 weeks from
lambing. Within each period, ewes were further allocated to four groups
(n=6) viz. initial slaughter; treatment with anthelmintic following by a
single infection with 20,000 larvae of Ostertagia
(Teladorsagia) circumcincta and slaughtered after 21 days;
chronic infection with 4000 larvae per day for 30 days or no infection.
Both these latter groups were again dosed with anthelmintic on day 50
and given 20,000 larvae on day 57 and slaughtered 21 days later. At the
start of each period 6 non-breeding ewes were challenged with 20,000
larvae and slaughtered 21 days later. All ewes were housed indoors.
Significantly higher worm burdens were found at all times in response to
challenge in breeding ewes compared to non-breeding ewes, except during
period 4 (12 weeks after lambing) where differences were non-
significant. Host suppression of faecal egg output was seen during
periods 2 and 3, with egg output being reduced by 50% and 95%
respectively, compared to that seen during period 1. Faecal egg counts
and worm burdens of previously infected ewes were lower than their
initially non-exposed counterparts (P<0.01). Even though immunity was
relaxed during late pregnancy and early lactation exposure to infection
was nevertheless important in stimulating the re-establishment of immune
competency.
Keywords: NZSAPAB;
Ostertagia; artificial; challenge; parturition; breeding
ewes; nematode; parasites; susceptibility
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Last Updated 25-01-1997
