are most susceptible to the effects of
challenge from transfer extending to
onset of lay.
Monitoring—Serology is a practical way to ensure that flocks are im-
pullet program. Once baselines are established, low titers suggest improper
vaccination or high titers indicate field
challenge. In general, a live program
should yield ELISA geometric mean
FIGURE 2. TYPICAL MG PLATE POSITIVE REACTIONS AFTER AN MG BACTERIN ADMINISTERED BY
INJECTION AT 12 WEEKS OF AGE.
If the vaccination program is adequate to the level of challenge, there should be no
drop in production concurrent with a rise in titer.
munized—not just vaccinated. Flocks
should be sampled just prior to housing to measure their response to the
titers (GMT) between 2,500-4,000
ELISA prior to housing. A combination live-killed program generally
should result in titers of 5,000 to 8,000
ELISA units, approximately three to
four weeks after the killed injection.
Figure 1 shows how inadequate administration of vaccine (birds with dye
on feathers receive only a partial dose)
can influence serology. Titers should
be monitored at 15-week to 20-week
intervals during production.
Shortly after housing, IBV titers typically spike from exposure to the resident virus on the farm. The levels then
gradually decline as circulating immunity wanes. If IBV is suspected as
being responsible for lowered production or egg quality issues, SPF cockerels can be placed as sentinels together
with newly housed flocks.
One week after placement, sentinels
are sacrificed and tracheal and lung tissue is submitted for attempts at virus
isolation or PCR assay to confirm the
presence of RNA fragments characteristic of IBV. Blood samples can be
collected from remaining sentinels two
and three weeks after transfer for serologic assay using the strain specific
hemagglutination technique. If virus
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