Issue |
Vet. Res.
Volume 31, Number 1, January-February 2000
|
|
---|---|---|
Page(s) | 95 - 96 | |
DOI | https://doi.org/10.1051/vetres:2000044 | |
How to cite this article | Vet. Res. (2000) 95-96 |
The production of PRRS negative pigs from multiple PRRS serologically stable herds over time using segregated early weaning (SEW)
A.M. Rajica, C.E. Deweya, A.E. Deckerta, R.M. Friendshipa, S.W. Martina and D. Yooba Population Medicine, University of Guelph, Ontario, N1G 2W1, Canada
b Pathobiology departments of Ontario Veterinary College, University of Guelph, Ontario, N1G 2W1, Canada
Abstract -
The objectives of this research were
to determine if it is possible to
produce PRRS negative pigs from multiple PRRS sero-positive herds over time using
segregated early weaning (SEW) and to evaluate serological stability of participating
breeding herds and the impact of sow vaccination on sow herd stability. The following
definitions were established. A vaccinated herd was considered serologically stable if
of the sow samples had PRRS ELISA S/P ratios
< 2.0. A non-vaccinated herd was
considered serologically stable if
of the sow samples had PRRS ELISA S/P ratios
< 1.0
and
of sow samples had PRRS ELISA S/P ratios
> 2.0 (modified from Dee.
Proc AASP, 1998; 409-411). Serological stability of ten PRRS sero-positive herds was assessed
by testing serum samples from 30 randomly selected sows per herd with an ELISA
(IDEXX). Piglets were weaned between 8 and 14 days of age and isolated in an off-site nursery
for 90 days. The procedure was repeated three times over a period of 14 months.
Pigs originating from non-vaccinated herds were housed separately from pigs obtained from
vaccinated herds. Serial blood tests of pigs were conducted at weaning and 30,
60 and 90 days of age. Serology was confirmed and clarified using PRRS RT-PCR and RFLP
assays. Littermates remaining on the farm of origin were also tested at weaning
and at 60 days of age. All closed vaccinated herds had
of sow samples with PRRS ELISA
S/P ratios
< 2.0. All piglets from these herds became negative after 30-60 days
and remained negative up to 90 days of age. The same results were obtained in the repeated
trials. Littermates remaining on the farm of origin had an active PRRS virus
(PRRSV) infection as demonstrated by rising S/P ratios in trial 1, but not in the repeated
trials. Two closed non-vaccinated herds had
of sow samples with PRRS
ELISA S/P ratios
< 1.0. One of these had
of sow samples with PRRS ELISA S/P ratios
>2.0.
The number of sero-positive piglets and their S/P ratio values increased
over time. In two non-vaccinated herds, piglets were PRRS virus positive at weaning. One
field and one intermediate strain of PRRS virus were identified. PRRS negative
pigs were produced from two stable, non-vaccinated herds. One open non-vaccinated herd had
56.7% and 10.0% of sow samples with PRRS ELISA S/P
< 1.0
and PRRS ELISA S/P
> 2.0,
respectively. PRRSV positive
piglets were detected at weaning in this herd. PRRS negative
pigs were produced after dams were vaccinated. The production of PRRS virus negative
pigs from multiple PRRS virus positive herds over time using SEW technology requires a
stable
breeding herd. Assessment of serological stability by the suggested criteria might be
very useful, but should not be overestimated. The consistent stability of vaccinated herds
observed in this study suggests that vaccinated herds are more likely to be stable
than non-vaccinated herds. Results need to be validated in large commercial operations.
Corresponding author: A.M. Rajic Tel.: (1) 519 824 4120 / 4070, 4873; fax: (1) 519 763 3117;
e-mail: , arajic@ovc.uoguelph.cacdewey@ovc.uoguelph.ca
© INRA, EDP Sciences 2000