MANAGEMENT
TIPS TO REDUCE PRE-WEANING MORTALITY
Dr. Donald C.
Lay, Jr.
Agricultural
Research Service, USDA
216 Poultry Science
Bldg
Purdue University
West Lafayette,
IN 47907
Pre-Weaning Losses
Data from the National Animal Health Monitoring System (NAHMS, 2001;
http://www.aphis.usda.gov/vs/ceah/cahm/Swine/swine.htm ) indicate
that the average number of pigs born per sow is 10.9, of which 10.0
are born alive and only 8.9 are able to survive until weaning. This
results in a 11% pre-weaning mortality rate. In comparison, NAHMS
data from 1990 and 1995 respectively, indicate that the number of
pigs born alive was 9.9 and 9.5, with 8.4 and 8.6 piglets weaned per
litter. So, although we saw a decrease in pre-weaning mortality between
1990 and 1995, we show a slight increase from 9% to 11% between 1995
and 2000. Because average litter size has slowly increased, we have
been able to realize a slow increase in the number weaned from 1990,
1995, and 2000; resulting in 8.4, 8.6, and currently 8.9 pigs weaned
per litter.
The NAHMS 2000
data indicate that of the 11% pre-weaning mortality, 52.1% die from
becoming crushed by the sow, 16.7% die from starvation, 11.5% die
from ¡°other known problem¡±, 9.3% die from scours, 7.4% from ¡°unknown
problem¡±, and 3% from respiratory problems. The majority of pigs are
weaned at 17. 2 days of age, with an average of 19.3 days of age.
Complex Interaction of Causes
Although the above data indicate that pre-weaning mortality is attributed
to very discrete causes, in reality piglets typically die from an
interaction of several possible causes of death. For instance, research
has shown that small piglets are more susceptible to cold and therefore
will lie more closely to their dam to obtain warmth. In this situation
it is easy to see that a piglet such as this may be more likely to
become crushed due to its proximity to its dam.
Similarly, piglets
that miss a meal due to being sick, injured, outcompeted at the udder,
or simply sleeping through a nursing bout, can enter an irreversible
spiral in which they become weaker, miss the next meal, and so on
until finally they starve to death.
Therefore, although
the cause of death may be listed as ¡®starvation¡¯, in reality it was
a combination of size, ability to maintain a constant thermal status,
a loud farrowing environment (possibly responsible for the pig missing
the nursing bout), and pathogens in the environment that all contributed
to the pigs death. Because of these complex interactions surrounding
almost all cases of pre-weaning mortality, pre-weaning mortality has
continued to hover around 10% for many years.
Parturition
The process of birth is the first area of concern in trying to decrease
pre-weaning mortality. The above mentioned data indicate that .9 pigs
per litter are born dead. Most of these deaths are due to still births
while the remaining are mummified fetuses which can be due to either
disease or intrauterine competition. As litter size increases, so
does the number of stillbirths.
In part this
is due to an increase in the length of parturition. As the length
of parturition increases, it is more likely that a piglet will be
subjected to a state of hypoxia (lack of oxygen). Not only can this
kill the piglet prior to birth but it also leads to piglets that are
born with a reduced viability. These piglets may then be more likely
to starve, become crushed, or diseased. In addition, as piglets are
delivered at a larger birth weight, length of parturition increases,
and likewise the chance of becoming hypoxic.
Having larger
litters can also increase pre-weaning mortality by contributing to
a large within-litter variation in piglet weight, thus allowing some
piglets to out-compete their siblings ¨C causing them to starve or
to become crushed.
Thermal Stress
One of the most significant stressors a pig experiences upon birth
is the challenge to adapt to the thermal environment. Unlike many
mammals, piglets do not possess brown adipose tissue, a type of fat
that enables newborn animals to generate a great deal of heat to maintain
body temperature. This fact, combined with very little subcutaneous
fat and a lack of a significant hair coat, ill-prepares the piglet
to enter a cold environment.
Thus the piglet
is required to stay close to the dam or a heat source to avoid hypothermia.
The shivering response is used as a back up response for the piglet
to generate heat in a cold environment; however, if the piglet has
been subjected to this much cold stress, it is already too much, and
likely to cause pigs to become susceptible to disease, starvation,
and crushing. The dam¡¯s belly provides an excellent heat source for
the newborn pig but positions it in a location in which it may easily
become crushed; without an adequate substitute heat source crushing
rates can be very high. The use of heat lamps has helped dramatically
to move the pigs away from the belly of the sow and into a safe area
to avoid crushing.
Unfortunately,
the piglets attraction to the heat lamp is not solidified until approximately
day three after birth. It is during these first three days after parturition
that most pre-weaning deaths occur. During the first three days after
birth, piglets have a high attraction to the dams udder and relatively
little attraction to the heat lamp.
Research has
shown that by transferring the odor of the dam to an area under the
heat lamp the, more piglets can be drawn to this safe area. More research
on how to attract piglets into a safe area can help to reduce pre-weaning
mortality.
As with the other
causes of piglet mortality, thermal stress has complex interactions
with many factors. For instance, small piglets are more susceptible
to hypothermia because of their surface to body volume ratio.
This coupled
with the fact that they are often outcompeted at the udder predisposes
them to starvation which can in turn predispose them to become crushed.
In addition, breed differences in tolerance to cold stress have been
noted. The Meishan, a breed imported from China, produces piglets
that are more resistant to cold stress than are Large Whites. This
difference is not due to the piglets possessing more fat or being
larger, they are actually much smaller, but due to the sow producing
a milk that has a much greater concentration of fat than does the
Large White.
This higher caloric
diet allows the Meishan piglet to produce more metabolic heat, and
therefore better withstand hypothermia.
Nutrition
Obviously, adequate milk production by the sow is critical for proper
nutrition of the piglets. As litter size increases it is important
not to lose track of this insight. Larger litters require a much greater
rate of milk production by the sow to ensure survival of the entire
litter.
Increasing the
quality of the milk that is produced is also a viable strategy to
increase nutrient availability to the piglet. Research has shown that
increasing the dietary fat of the sow during late gestation and early
lactation can increase the fat content of the colostrum and thus increase
survival of low birth weight pigs.
This is due to
the fact that increasing concentrations of colostral fat increases
the piglets¡¯ energy intake and therefore fat deposition. Total intake
of colostrum, however, is decreased. Another important factor in providing
quality milk for the piglets is to maintain an environment that allows
the sow to maximize feed intake. Environmental and disease stressors
can both contribute to decreasing sow feed intake. Heat stress is
especially capable of depressing feed intake. This poses a difficult
situation as the producer must balance the needs of the piglet for
a warm environment, with that of the sow for a much cooler environment.
Disease
Although the majority of pre-weaning losses are due to non-infectious
causes which are strongly associated with management practices, deaths
due to disease do occur and can be quite devastating.
As with all mammals,
the piglet is immunologically na?ve at birth and depends on the transfer
of maternal antibodies to provide it protection against disease. Therefore
ingestion of colostrum, the immunoglobulin-rich milk that is produced
maximally by 12 hours after parturtion, is critical for piglet survival.
After 48 hours of life, the piglet gut is no longer able to absorb
these protective immunoglobulins.
By 10 days of
age the piglet is able to produce its own antibodies and this provides
an overlap from the protection of the maternal antibodies which persist
for approximately 14 days. Any factor that decreases colustrum intake,
such as cold stress, can therefore predispose the neonate to succumb
to disease due to its lack of protection. Birth order can also influence
the amount of immunoglobulins a piglet receives. Because immunoglobulin
content of the colostrum drops by 50% within 6 hours of the initiation
of parturition, sows having larger litters and therefore a longer
farrowing duration may predispose their last born piglets to receive
a lower level of passive immunity. The endemic pathogen status of
the sow herd can also influence whether piglets are struck with disease.
Both bacterial and viral diseases are more likely in neonatal piglets
that are born to infected sows.
The Sow and the Pig
Because more than 50% of pre-weaning mortality is due to being overlain
by the sow, it is critical to examine sow maternal behavior. Researchers
have found that piglets are crushed when the sow changes position,
essentially moving between lying and standing and vice versa.
However, pen
housed sows also crushed a significant amount of piglets while changing
lying positions. Interestingly, evidence exists to suggest that early
experience affects maternal ability, as sows reared in group-housing
systems have been found to exhibit a lower piglet mortality rate.
Sows are capable
of exhibiting beneficial maternal behavior, and confinement has been
shown to prevent their natural ¡°anti-piglet crushing¡± behavioral repertoire
thus suggesting a reason for the variable success of crates.
An outstanding
anomaly in the piglet mortality problem is that the majority of sows
do not respond to the distress vocalizations of their piglets when
they are being crushed . However, sows which are responsive to piglet
distress calls are better able to release trapped piglets prior to
crushing.
One theory to
explain the non-responsiveness is that sows in farrowing crates are
subjected to the distress vocalizations of neighboring piglets, and
regardless of their responses they can not make the neighboring piglet
stop vocalizing and thus they learn to be non-responsive when piglets
vocalize.
Housing methods
to reduce crushing may have met with variable success largely because
research efforts have concentrated on controlling and(or) altering
the behavior of the sow and have largely ignored the piglets¡¯ role
in crushing mortalities.
Another anomaly
in pre-weaning piglet deaths is due to savaging of piglets by the
sow. Savaging behavior is characterized by a sow that is overtly aggressive
to her piglets, and may result in injury and death to a portion of
the litter. In a comprehensive survey of commercial gilts, researchers
evaluated the incidence of savaging and some factors that are correlated
with this deleterious behavior.
These data reveal
that 5.3% of gilts expressed piglet directed aggression with 2.9%
of these gilts fatally savaging at least one of their piglets. Aggressive
behavior of gilts to their offspring resulted in .6% death loss and
.14% of piglets were injured. Interestingly, these authors found that
if the lights were left on in the farrowing house, a reduction in
the incidence of savaging was realized. Additionally, animals who
savaged piglets as gilts were more likely to savage during their second
parity. Data indicate that savaging sows are more fearful of humans
and that sows that readily interacted with humans were non-savaging
and more protective of their litters.
Fear of the piglets,
lack of experience during adolescence, and the pain associated with
parturition, have all been implicated in savaging behavior, however,
the definitive cause(s) of savaging remains elusive.
Facilities
The initial move to decrease piglet crushing consisted of confining
the sow to a smaller pen than was traditional. The incidence of crushing
and related piglet mortality has significantly decreased since the
popular adoption of the farrowing crate in the 1950s. Indeed, most
studies have found that housing sows in a small pen, or farrowing
crate, does decrease piglet mortality.
This management
practice gained momentum in the 1960¡¯s as more economic pressures
were applied to the swine industry. Unfortunately, piglet crushing
remains a problem for swine producers.
Data from NAHMS
indicates that the rate of piglet crushing has remained at a high,
stable rate from 1991 to 2000. The incidence of pre-weaning mortality
continues to represent a significant source of economic loss to the
swine industry. Interestingly, approximately 50% of these pre-weaning
death losses occur during the first three days of life.
Many experiments
have been conducted to investigate the effect of the design of the
sow¡¯s housing during farrowing in reducing preweaning mortality. The
typical farrowing crate of approximately .6 m x 2.2 mis the prevalent
form of housing today, but animal well-being continues to stimulate
interest in the farrowing pen. But, crate design has been found to
influence piglet mortality as research has found more crushing in
wide crates (64 cm wide) than in narrow crates (55 cm wide). Unfortunately,
relatively little work has been conducted to determine the effect
of gestation housing on subsequent piglet survival.
One major reason
changes in pen sizes and shapes may not have been successful in decreasing
crushing is because piglets are attracted to their dam¡¯s udder immediately
upon birth and prefer to lie there the majority of time during the
first three days after birth.
After this initial
three days, piglets are often seen using the heat lamp instead of
the sow¡¯s udder. This change of preference for lying area may help
the piglets avoid death due to crushing. Although the sow¡¯s housing
environment has been shown to have a profound effect on piglet crushing,
the physical constraints of the sow and the behavior of both the sow
and piglet should not be overlooked.
Management Tips
The biggest, most important act a producer may due to decrease pre-weaning
mortality is to have a stockperson present during farrowing. Concern
and vigilance during this time ensures that struggling piglets find
the udder and are able to consume adequate colostrum. In addition,
piglets that would be crushed can be placed in a safe spot under the
heat lamp until they are able to maneuver well and compete for a teat.
Those pigs that appear less viable and need the extra time under the
heat lamp can be taken care of to ensure that they do not become hypothermic.
In addition, while attending the farrowing sow, attention to her neighbors
who may have already farrowed can help save their piglets as well.
The thermal environment
is probably the second most critical aspect to which to attend. Ensuring
that the sow is not too hot and that the piglets are plenty warm can
be tricky. However, success in both areas will allow the sow to have
a maximum feed intake which will provide the pigs with greater nutrition,
and it will help the pigs combat the challenges of malnutrition and
disease.
As always, a
clean environment goes a long way in providing a disease free state
for both the sow and the piglet. Sow health can not be overlooked.
Unhealthy sows, lame sows, and sows with pressure sores are less likely
to be adept at lying and responding to their piglets and thus have
a higher incidence of crushing.
Authors Note: For a more comprehensive review of this topic refer
to Lay et al., 2001 (JAS, 2001)
Articles
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