Agriculture Reference
In-Depth Information
Catastrophic events that kill large numbers of sows can occur in modern confinement
buildings. The two most common causes are electric power failure causing the mechanical
ventilation system to stop, resulting in a sudden rise in temperature and death loss due to
heat stress, and secondly accidental asphyxia due to manure gases rising from the manure
pit, usually caused by agitation of the manure in the absence of adequate ventilation.
18.5
Infectious diseases affecting the health of sows
The following is an overview of some of the common and important diseases affecting
sow health, arranged according to body systems.
18.5.1
Reproduction
Sows tend to have a high conception rate of around 90% on most modern, well-managed
pig farms and they produce large litters of piglets. In recent years the introduction of
hyperprolific breeding lines has resulted in average litters of 15 or more pigs born per
farrowing being common. Disease can impact the conception rate, and the survival of
embryos and fetuses. The result of mortality of the products of conception can be expressed
as regular and irregular returns to estrus, abortion, or small numbers of pigs born per
litter. A regular return to service is defined as a sow that comes into heat around 21 d after
having been bred, whereas an irregular return refers to a sow that shows signs of heat
>24 d after the initial breeding. The presence of mummified or stillborn piglets among
a small number of live pigs is indicative of disease within the uterus during pregnancy.
Certain diseases tend to leave their own distinctive pattern of reproductive failure. For
example, parvovirus and enterovirus infections cause a pattern that has sometimes been
described as SMEDI, a short form for stillbirths, mummified fetuses, embryonic death
and infertility. Fetuses can mount immunity against parvovirus after about 70 d from
conception so that only small mummified piglets (<17 cm crown-rump length) are born
to sows infected with parvovirus during pregnancy. The fetal skeleton begins to develop
after 35 d post-conception, prior to skeletal formation the embryos are reabsorbed and
don't appear at birth as mummies.
Abortions tend to be uncommon in sows. They can be triggered by non-infectious causes
such as restricted feeding combined with sudden cold stress, sunburn, and following
high fevers (pyrexia). Infectious diseases (such as PRRS and leptospirosis) that cross the
placenta, kill the fetuses, and cause abortion, generally affect sows in the last trimester
of pregnancy. Diseases that are associated with late stage abortion are also generally
characterized by stillbirths and/or weak-born piglets.
Common swine reproductive diseases can be prevented by vaccination at 4 and 2 wks
prebreeding for gilts and at weaning for sows. Routinely used commercial sow vaccines
contain Leptospira sp. Erysipelothrix rhusiopathiae and parvovirus. In certain situations
PRRS virus vaccine prior to breeding may be used as well, although the currently available
PRRS vaccines have poor efficacy.
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