Agriculture Reference
In-Depth Information
18.2
Management of disease in the sow population impacts
the entire herd
The control of many swine diseases depends on the sow herd providing immunity to
piglets against all the important pathogens present on the farm, and at the same time
not transmitting any of these pathogens to the piglets. In other words, each sow in the
herd is not only providing nutrition to her piglets but also passive immunity through
immunoglobulin-rich colostrum and milk as well as providing piglets with a healthy
microbial flora. As herd size increases the achievement of strong overall herd immunity
becomes difficult. Subpopulations of sows that have not been exposed to an endemic
pathogen can easily exist in a large herd. If a sow with no exposure to a pathogen farrows,
her litter will not receive passive protection to protect the litter from that pathogen,
leaving them more vulnerable to infection than piglets from immune sows. The piglets
that did not acquire passive protection might encounter the disease in the first few weeks
of postnatal life and be overwhelmed by infection. These infected pigs might become very
sick and die, but they are also likely to spread large numbers of the pathogen to other
pigs and to the environment as well. The disease challenge for all piglets in the farrowing
room is increased in this case and contamination of the environment might pose a threat
to subsequent litters using the same farrowing crate. In addition, sick piglets may carry
disease into the nursery or even the grower-finisher barn. Sows that become exposed for
the first time to a pathogen during the last stage of gestation are likely to be a source of the
pathogen and infect their litter. Therefore, there should be a great deal of effort placed in
ensuring that the entire sow population has immunity to the endemic pathogens present
in a herd. This is particularly important for the young replacement gilts that are entering
the breeding herd and are possibly being exposed to different micro-organisms for which
they have no immunity.
In general, sows gain immunity by encountering the potential pathogens through mixing
with other sows or from encountering the organisms in the environment. When farms
are small and extensive-rearing is practiced, it is relatively easy to ensure that all sows are
exposed to the same organisms and that there are no subpopulations of naive animals.
However, modern intensive confinement facilities make it more difficult to expose young
breeding stock to all the possible diseases present on the farm. Strategies to accomplish
sow herd immunity include purposeful exposure (particularly useful for replacement
gilts held in quarantine facilities) and vaccination. In addition, there should be emphasis
placed on preventing new diseases from entering the herd (biosecurity).
One of the greatest risks for a new disease entering the sow herd occurs when replacement
breeding animals are introduced. The health status of the source herd must be as similar
as possible to that of the recipient herd. A single source of replacement animals is always
preferable to multiple sources. Incoming gilts should be housed in a quarantine facility
before entering the main herd. The main advantage of using a quarantine barn is that if
the gilts were subclinical carriers of a disease it might be quickly diagnosed and the gilts
can be shipped to market instead of being integrated into the main population, and thus
infecting the entire herd. But the quarantine barn also provides an opportunity to expose
the gilts to potential disease-causing agents that may be present in the recipient herd
