Farrowing
Management and Piglet Losses
Piglet Mortality
When do losses of piglets occur and why?
The loss of embryos
and fetuses during pregnancy, and loss of piglets at birth, has been
well documented in swine and in swine production systems. Approximately
40% of potential piglets are lost as embryos and fetuses before day
40 of gestation.
The reasons for
these high rates of litter reduction may be a natural mechanism to
ensure pregnancy can be maintained or some piglets are born to sustain
the species, or may result due to defective embryos, unfavorable uterine
environments, and fetal competition for space. At a much lower frequency,
some fetuses die in the uterus before farrowing. These undergo degeneration
and depending upon when they are lost during gestation, may appear
as mummified very small or almost normal sized fetuses at birth. Pigs
that are fully formed, but fail to survive the birth process are classified
as stillborns.
How common are stillborns?
Stillborns average 6 to 7 % and but range anywhere from 5 to 10% across
farms. 1999 PigCHAMP summary data indicates the US average is 0.2
mummified fetuses and 0.8 stillborn pigs per litter. It is reported
that the USA has a higher stillborn and preweaning mortality rate
than other parts of the world. This is thought to be due to the lower
number of farrowing personnel to sows, which can often exceed 1:250.
It is suggested that a 1:30 ratio could reduce the incidence of stillborn
pigs. In herds where stillbirths are higher than 10%, it is suggested
that infectious causes should be investigated.
Stillbirths are related to dystocia or difficult birth during farrowing.
Stillborn pigs are not identified as the runts in a litter and are
observed to occur more frequently in litters with less than 5 pigs
and when more than 14 are born in a litter. Stillborns are observed
to be low when 8 pigs are born (.04) but this number increases as
litter size increases. Stillborns may occur due to premature rupture
of the umbilical cord, early detachment of the placenta from the uterus,
or restricted blood flow to the piglet during intense uterine muscle
contractions, or during passage through the pelvic canal.
It is also observed
that the umbilical cord can get wrapped around the piglet's body and
get pinched or closed off in the pelvis. Stillborns are also observed
to increase when farrowing is induced earlier than day 112 of gestation
or if gestation is prolonged past day 116.
What is the ultimate
cause of piglet loss?
The fetal lungs acquire the ability for gas exchange at birth. Major
changes in lung development occur at days 95-100. During the birth
process and soon after liquid is removed from the lung. It has been
estimated that the physiologic half-life of oxygen is less than 5
minutes and irreversible brain damage occurs within 5 minutes of umbilical
rupture or even impeded blood flow through the umbilicus. It is thought
that 93% of all intrapartum deaths are due to umbilical rupture since
most stillborn pigs have broken umbilical cords. Fetal hypoxia (lack
of oxygen) is most related to piglet survival at farrowing and even
temporary hypoxia during birth may cause permanent brain damage and
reduce liveborn pig survival. Pig fetuses are very susceptible to
intrauterine asphyxia.
A period of prolonged
intrauterine hypoxia caused by uterine hypertension (high pressure
due to contractions) could deplete energy stores (glycogen) needed
by the piglet after birth to survive. Most of the pig's glycogen is
found in skeletal muscle and this is essential both for movement and
temperature regulation. In cases of intrauterine asphyxia, inhalation
of fetal meconium (feces) is very common, and 87% of stillborn pigs
that die by asphyxiation, have meconium in the oral cavity.
The duration of parturition is highly related to stillbirths and therefore
short deliveries are considered highly desirable. As duration of farrowing
increases from 1 to 8 hours, stillbirths increase from 2.5 to 10.5%.
Interestingly, more than 2/3 of all stillbirths occur in farrowings
lasting less than 4 hours. Over 80% of stillborn losses occur in the
last 1/3 of the litter in sows. Stillbirths in gilts can occur more
frequently in the first two pigs born. The stillbirth rate increase
as the interval between pigs exceeds 20 minutes.
The average birth
interval between successive live pigs is 13 to 18 minutes but between
a live pig and stillborn pig is 45 to 55 minutes. However, the intervals
are longer between the first two and the last two pigs born in a litter.
Generally speaking the last pig born has less than a 50% chance of
survival in any litter. Most piglets must leave the space they occupied
during pregnancy and enter empty space previously occupied by a delivered
pig. From there, they move through the uterine body, the cervix, and
the vagina, and finally exit though the vulva.
The umbilical
cord is 60 to 75 cm long and if the 120-180 cm of the uterus does
not shorten sufficiently after emptying, then rupture of the cord
is inevitable. Therefore delivery must subsequently occur within 5
minutes of rupture. Umbilical rupture or premature placental detachment
is thought to occur in 20% of stillborn pigs from the first third
of the litter and involve up to 50% of stillborn pigs in the last
1/3rd of the litter.
It is not known whether prostaglandin administered during farrowing
at this stage, could improve the process.
Stresses on the sow and stillbirths.
Temperatures above 30 ˇăC in late gestation from days 102 to 110 increase
rate of stillbirths and reduce piglet birth weight. The mechanism
for this remains unknown however. Lack of feed and absence of nesting
material is also suspected of increasing sow stress levels. Stress
has been shown to reduce oxytocin levels during parturition, which
would tend to prolong delivery. Therefore it is important to provide
conditions that will allow the sow to remain calm and comfortable.
How can you tell
if pigs were stillborn?
Stillborn pigs appear normal but they can be distinguished from other
pigs that were born alive and died later after birth by the lung flotation
test. This test requires the lungs to be dissected and placed in water.
If the lungs float, the pig had air trapped in its lungs and was born
alive and breathed. If the lungs sink, they contained no air and the
animal never breathed. Stillborns can also be classified into type
I, which are prepartum deaths due to infection, and type II, which
are stillborns that occur during parturition, which are usually non-infectious.
Is lack of uterine
contractions involved in stillbirths?
Uterine inertia is rare even during prolonged delivery. However, in
cases where this was identified, administration 10 I.U. of oxytocin
returned the pattern of contractions to normal for ~10 to 15 minutes.
However, this induction of massive contractions could potentially
disrupt blood flow to the placenta.
Can any treatments
reduce stillbirths?
- Assisted births
An assistant present at farrowing can reduce the incidence of stillbirths.
Obstetrical assistance will minimize stillbirth rates, and inducing
farrowing during the normal working hours will improve the frequency
of observed farrowings. It has been reported that ~25% all stillborn
pigs can be revived by artificial respiration using a small funnel
over the snout. In addition, during assisted farrowing, an attendant
can successfully remove fluid and mucus that obstructs the pig's airway
and facilitate normal breathing. It was observed that 18 hour farrowing
supervision through the night and continuing into the daytime, increased
the number of pigs saved.
- ACTH
ACTH (25 to 60 I.U.) administered to sows i.m. on day 110 has been
shown to reduce duration of parturition and reduce stillbirths by
40-50% (0.2 pigs/litter saved). This thought to be related to increased
corticosteroid levels reaching the fetal lungs and gut and facilitating
precocious maturation. Estradiol benzoate given to sows also was reported
to reduces stillborn rates. It was suspected that estrogen increased
muscle gap junctions, increased oxytocin receptors, and relaxin receptors
in both myometrium and cervix. This collectively improved the ability
to deliver live piglets.
What are the
factors involved in live piglet loss?
Mortality of pigs born alive results from a variety of causes. The
industry has set a 10% death loss as acceptable and USDA and PigCHAMP
figures indicate a 10 to 14% range for pre weaning mortality. Producers
in the top 90th percentile in production records have a preweaning
mortality of 8.3%. Of pigs that are liveborn and subsequently die,
>50% die within 4 d of farrowing. These typically involve weak
pigs that are crushed and die of starvation. Mortality in liveborn
pigs is also associated with sows that farrow early, especially those
that are induced to farrow on d 110 compared to 112. At day 109 of
gestation, piglets can be delivered but many pigs do not survive past
one day post-partum. Even pigs from days 110-111 have reduced survival.
Colostral Immunity
and Milk
Immunity for the piglet is not obtained through placental transfer
of antibodies during gestation and therefore it is born with very
limited immune protection. Further, the piglet has finite reserves
of body energy and may even be energy deficient after a long and stressful
delivery process. It then becomes even more critical for the piglet
to obtain both antibodies and energy through the colostrum soon after
birth. The piglets should begin to suck within 10 to 35 minutes of
birth. If they fail to do so, they can be helped to nurse or even
given colostrum.
Colostrum will
serve to protect the piglet against a host of microbes and also allow
it to cope and survive in its new environment through the energy expending
activities of nursing, seeking warmth, and moving to prevent being
crushed by the mother. Nursing soon after birth and nursing as frequently
as possible are highly advantageous for piglet survival since the
newborn obtains antibodies only through colostrum ingested within
the first 24 h after birth.
Antibodies in
the mother's milk are very high at this time and when ingested, are
readily absorbed.
The antibodies
in the gut also serve to provide protection within the gut of the
piglet. After 24 h, gut acids in the piglet begin forming and stomach
pH lowers. After this time period, immunoglobulins from the mother's
milk cannot pass through the gut wall and are destroyed. Thus, only
the antibodies that are obtained in this manner during this short
period will serve to protect the piglet over the next few weeks.
What other factors
can help reduce preweaning mortality?
Use of heat lamps. Three lamps used strategically have been shown
to be beneficial immediately near the time of birth. Lamps placed
behind, and on the sides of sows, but which do not place excessive
heat on the sows, can improve piglet survival. Keep all three on during
farrowing, and then remove the one behind when farrowing is completed.
This will keep
pigs from getting or staying behind the sow where they are prone to
be crushed when the sow sits down. Then remove the second side lamp
at 48 h, which will keep the pigs located to only one side for warmth.
If open flooring is used in the farrowing crate a floor mat should
be used to reduce drafts on the pigs.
What about crushing?
Crushing has been linked to sow behavior, crate style, size of the
sow, and weak pigs. Piglets that suffered hypoxia or dystocia will
deplete their body stores of oxygen and even energy more quickly.
These pigs will be born weak and may therefore be the ones that are
too weak to move and are more susceptible to crushing, chilling and
starvation. Crates have been shown to reduce crushing by 3% compared
to outdoor systems.
Crushing remains
a serious problem and crate design may be an important aspect. Reports
have indicated that free stall crates may crush more pigs than more
restrictive crates. Further, more sophisticated crates, that utilize
hydraulic cylinders or other mechanisms to slow the sow's when lying
down, can reduce pig loss by 0.8/litter.
Other methods
to reduce crushing have involved the use of raised flooring in the
center of the crate to prevent the frequency and ease of pigs being
there when the sow lies down.
Articles
99
