Agriculture Reference
In-Depth Information
and not in the source herd. The gilts may go through a mild form of the illness during
which time they shed high numbers of pathogens and then develop strong immunity.
Sometimes there are diseases on the recipient farm that pose a serious health threat to
the incoming gilt. The quarantine period is a good opportunity to vaccinate the gilt for
diseases that pose a health threat to the incoming gilts so that they don't become seriously
sick when they are mixed with the resident breeding stock.
Young sows are likely to have less immunity than older sows, making the vaccination of
gilts a priority. From an immunity standpoint, it is better to have a low sow turnover with
as few gilts introduced to the breeding herd as possible. Closing the herd to incoming
animals for a period of several months is an important part of a strategy to control
or eliminate some swine diseases, for example transmissible gastroenteritis (TGE) or
porcine reproductive and respiratory syndrome (PRRS). Both these diseases are caused
by viruses, and in both cases vaccines are not very effective. It is generally accepted that
in the case of a sudden outbreak of diseases such as these, exposure of all sows to the
pathogen as quickly as possible is desirable for the development of herd immunity. This
widespread exposure to the pathogen ideally creates a uniformly immune sow herd. The
immune sows will be able to protect their piglets from disease, and prevent the spread of
disease from suckling pigs into the nursery. This is considered an essential first step for
the elimination of a disease from the herd. During the time of purposeful exposure and
spread of the disease to all sows it is essential that the breeding herd is closed to all new
introductions of replacement breeding animals. Only after it can be demonstrated that
the virus is no longer being transmitted in the sow herd, and that it is no longer present
in the environment, is it safe to begin introducing new animals into the herd.
There are many other ways by which disease can enter a herd and managing that risk has
become extremely important in modern swine production. There are numerous risk-based
methodologies that have been developed to help in the design of biosecurity programs
for swine farms (Neumann, 2012). Major risk factors, in addition to the introduction of
replacement breeding stock, include; livestock and feed trucks, birds and rodents, and
human foot-traffic in and out of the barn. Resource documents outlining essential steps
in farm-level biosecurity are readily available from producer and veterinary organizations
as well as government extension services.
18.3
Managing health of the sow
In general, individual sow health is often neglected relative to that of the rest of the
herd. Mortality rates and culling because of sickness and injury may exceed 10% on
many modern swine farms (Abiven et al. , 1998). Health programs tend to be aimed at
reducing losses in the suckling and post-weaned pig and relatively less attention is paid
to maximizing the health of the individual animals in the breeding herd. The purpose
of many vaccines given to sows is to maximize the quality of the passive and lactogenic
immunity that the sow will transfer to the suckling piglets, for example vaccines that
prevent diarrhea caused by Escherichia coli (colibacillosis) in newborn piglets. Other sow
vaccination programs are primarily designed to reduce the losses associated with fetal
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