March, 1998 . Volume 21, Number 2
March, 1998 . Volume 21, Number 2
The Problem
Number of litters produced per sow per year and through-put
in farrowing facilities are maximized by early weaning and prompt
rebreeding of the weaned sow. Earlier weaning on swine farms continues
to occur because of development of cost-effective nursery diets
and construction of modern facilities that maintain well-being
of neonatal piglets. Today, it is possible to raise pigs successfully
and economically after weaning as early as 1 week of age; however,
weaning too early results in potential problems in managing the
weaned sow.
The sow must be able to complete several physiological processes
to breed back successfully after weaning. Thus, for the sow to
breed back promptly after farrowing:
Management Steps for Early-Weaned Sows
This paper will deal with management strategies for sows early-weaned
at various times postpartum.
Weaning from Day 0 to 2
Weaning at farrowing (zero weaning) or during the first 2
days postpartum does not permit sufficient suckling to occur to
assure that LH and FSH are suppressed and that the large ovulatory-sized
follicles present at farrowing have undergone regression. As a
result, the follicles that are present at farrowing may continue
to grow and become cystic. This leads to prolonged or irregular
estrus and prolonged infertility. Many sows weaned during the
first 2 days after farrowing will not breed back normally until
5 to 8 weeks postpartum.
If possible, one should avoid weaning during the first 2 days
postpartum so the litter can suppress gonadotropin secretion and
cause the large follicles present to regress (Figure 1). If this
is not possible, ovulation of follicles present at farrowing can
be induced in a high percentage of sows by treatment with 500
to 1,000 IU of hCG about 12 to 24 hours after farrowing (T.A.
Armstrong, W.L. Flowers and J.H. Britt, unpublished observation).
Or sows can be treated with PG600 2 days after farrowing followed
by treatment with hCG 48 h later. Sows induced to ovulate during
the 1st week postpartum return to estrus at somewhat irregular
intervals, mostly around the 4th or 5th week postpartum. Fertility
of these sows has not been studied sufficiently to know how it
compares with sows weaned at 2 to 4 weeks postpartum. We currently
have studies underway to determine whether estrus can be induced
to occur at a more predictable time in these sows by treatment
with luteolytic prostaglandins at 14 to 16 days after induction
of ovulation.
Another potential strategy for delaying estrus and permitting
the large follicles to regress involves treating sows with Altrenogest
(15 to 20 mg/day) for 10 to 14 days after weaning on days 0 to
2. Altrenogest is an orally active progestogen, which suppresses
gonadotropin secretion like progesterone does during the estrous
cycle or pregnancy. The suppression of gonadotropins leads to
regression of the large follicles and subsequent development of
normal follicles. Sows will usually come into heat 4 to 6 days
after withdrawal of Altrenogest from the feed. Altrenogest has not
been approved for use in pigs in the United States but FDA approval
is pending.
Since follicle growth and oocyte quality are influenced by
energy intake, it is important to feed early-weaned sows to promote
normal follicle development. Basically this means that sows should
be fed to avoid weight loss until they are bred (Figure 1).
Weaning from Day 3 to Day 14
Sows weaned after day 2 are likely to have suppressed LH and
FSH at weaning. Once FSH and LH are suppressed, large follicles
on the ovaries regress and these are replaced by very small follicles
(<3 mm diameter). When weaning occurs, the increase in LH and
FSH that follows should stimulate growth of these small follicles,
leading to estrus in about 6 to 10 days.
If weaning occurs during the 2nd week postpartum, then sows
are likely to come into heat during the 3rd week. Split-weaning
of the litter may promote earlier re-breeding in early-weaned
sows, particularly during summer when postweaning anestrus leads
to a delay in return-to-estrus (Figure 1). For split-weaning,
an interval of 2 days is ideal between weaning the heaviest half
of the litter and weaning the lightest half. During this 2-day
period there is an increase in LH and FSH associated with reduced
suckling intensity; however, if the lightest pigs are allowed
to continue to nurse beyond 2 days, they will begin to suckle
both the occupied teats and the teats vacated by the heaviest
pigs and this will result in a compensatory increase in suckling
intensity and gonadotropins will be suppressed.
Sows weaned during the 2nd week postpartum also may benefit
from treatment with PG600 at weaning to stimulate a prompt return
to estrus (Figure 1). In one study when sows were weaned between
days 5 and 11 postpartum, more PG600-treated sows than untreated
sows came into heat within 10 days after weaning (75% vs. 21%)
and the interval to heat was shorter (4.1 vs. 5.9 days). The PG600-treated
sows also had a higher ovulation rate (22.2 vs. 17.7 CL) and more
viable embryos 11.5 days after breeding (16.4 vs. 10.9). Another
strategy is to use PG600 only in sows that have not returned to
estrus by 7 days after weaning. This strategy permits sows that
would return to heat spontaneously to do so without the treatment,
but it permits active stimulation of potentially anestrous sows
in time to get them bred back with minimal delay.
If sows are to be bred on the first heat after weaning, survival
of embryos may be enhanced by treatment with 1 million IU of vitamin
A at weaning (Figure 1). In one study, embryo survival 11.5 days
after breeding tended to be higher in vitamin A-treated sows than
in controls (78% vs. 66%).
It is essential to feed sows all they will eat from weaning
until estrus to promote maximal follicle growth (Figure 1). Sows
will continue to synthesize milk for a few days after weaning
and this can lead to a catabolic state if feeding is restricted.
Follicle growth is affected by feeding during the 1st week postpartum,
so it is important to monitor feed intake in early-weaned sows.
Usually these sows will be moved to the breeding barn where restricted
feeding may be practiced; however, early-weaned sows should be
fed all they will consume until they come into heat, and then
feed intake should be reduced to about 1.5 times maintenance.
Weaning after Day 14
Weaning after day 14 usually results in a tighter synchrony
of postweaning estrus and higher fertility at that estrus compared
with weaning earlier.
Most management procedures that are useful for sows weaned
between days 3 and 14 also apply for sows weaned after day 14.
Feeding during lactation may be more critical for sows weaned
after day 14 than for sows weaned earlier because the sow has
reached peak milk production and body weight loss may be greater.
Sows in a more catabolic state during lactation return to estrus
later, have lower ovulation rates and lower embryo survival rates
than sows that have a higher energy balance.
In situations where postweaning anestrus is a serious problem,
such as in start-up herds with all primiparous sows in later summer,
use of PG600 in all sows at weaning may be appropriate to keep
pig flow at the desired level and to prevent accumulation of nonproductive
days in open sows. Split weaning may also be useful in these situations.
Treatment with vitamin A at weaning will also benefit subsequent
litter size, and under certain circumstances, may be beneficial
in promoting earlier rebreeding and higher conception rate.
Jack Britt
Swine Health Summit
Williamsburg, VA
November 12-13, 1997
Adapted by Todd See
The rapid implementation of Segregated Early Weaning (SEW)
in the US swine industry has posed some new challenges to the
health of piglets and those caring for them. Many problems stem
from imposing strict maximum ages at weaning, regardless of piglet
body weight, to prevent disease transmission and achieve the eradication
of certain endemic infections during the growing life of the pig
(i.e. Actinobacillus pleuropneumoniae).
Perhaps we have improbable expectations for the complete
elimination of pathogens and placing excessive faith in the early
weaning "magic" and forgetting the principles of good
production. This is particularly true when commingling from multiple
sources or in nurseries that house multiple age piglets. In addition,
early weaning will increase labor and feed costs to care for these
smaller and younger piglets in the nursery. Importantly, we must
remember that normal biological differences in body weight at
birth, become heightened from weaning to slaughter, particularly
in All-in-all out production and may lead to variation in weight
gains during the growing phase. "Sort loss" and prolonged
close-outs in finishing units can be the ultimate consequence.
On the positive side, SEW will allow a reduction of exposure
to pathogenic microorganism endemic to the sow herd, reducing
the incidence of costly diseases. Growth rates particularly in
single source nurseries can be exceptional (Average daily gain
above 400 g). There is also evidence that SEW piglets have increased
thymus size when compared to conventionally reared piglets. The
thymus is responsible for development of the immune system and
production of growth hormone, and a greater thymus/body weight
ratio may explain the improved growth rate.
General Principles When Dealing With Lightweight Pigs
2. Employ a herd approach to the analysis of the problem,
but apply individual pig care for prevention and resolution.
3. People really make a difference. We need stockpeople with
husbandry skills, pride in their work and attention to detail.
4. Disease has a major impact on weight variability. Implement
routine herd health checks and use targeted diagnostic investigations.
5. Rapid detection and treatment of the disease or injured
pig, with humane culling if required.
6. Recognize the influence of genotype on growth potential,
particularly when setting target weaning weights at fixed ages.
7. Realize problems are seldom simple, but rather a combination
of disease, nutrition, management and stockmanship.
Minimizing Lightweight Pigs at Weaning
Reasons why piglets may be below the target weaning weight:
Oliver Duran
1997 Swine Health Summit
Adapted by Todd See
January 21, 1998
TO: N.C. Swine Producers
FROM: Dr. George C. Edwards, State Veterinarian
RE: PSEUDORABIES ERADICATION
The U.S. Department of Agriculture is expected to implement
changes in the national pseudorabies program by April 1, 1998
that will significantly impact North Carolina's pseudorabies program.
North Carolina regulations adopt the federal regulations by reference.
When changes in the federal regulations become effective, they
automatically become effective in North Carolina.
Regulatory officials are currently working with infected herd
owners to remove as many positive animals as possible prior to
the national changes. The purpose of this communication is to
advise you of these important changes and encourage each producer
to intensify disease prevention methods to include isolation and
testing of all herd additions prior to adding animals to your
herd.
These changes require swine
producers to test and remove all infected sows at weaning and
all infected boars quarterly. These regulatory changes are designed
to remove all positives within one breeding cycle to accomplish
the national goal of PRV eradication by the year 2000.
Your efforts in accomplishing these goals will promote the
demand for North Carolina pork by avoiding additional interstate
and international trade restrictions.
GCE/bb
Morgan Morrow
The National Research Council (NRC) is in the process of updating
their publication on "Nutrient Requirements of Swine".
The previous publication was published in 1988 and has been widely
used by scientists and others interested in swine. However, significant
progress has been made in genetic selection, increasing lean,
and management techniques (for example early weaning). These changes
have prompted the NRC to revisit the nutritional requirements
of pigs and update their publication to include the latest research
information. The new publication will include:
The NRC is planning a 2-day satellite symposium to update
interested audiences on new discoveries in the biology of swine
and how they influence nutritional requirements. In addition,
computer modeling demonstrations and case study workshops will
be held to familiarize participants with the Nutritional Software,
followed by a panel discussion.
North Carolina State University will host a satellite downlink
and put together a program to introduce this new publication.
The program is targeted for professionals in the field of swine
production, including consulting nutritionists, professional animal
scientists, feed company nutritionists, feed additive industry
representatives, practicing and professional veterinarians, field
swine specialists, extension specialists, university nutritionists,
and professionals involved in educating both college students
and the general public.
The program is scheduled for April 14 and 15, 1998. Specific
details on the program format, times, and costs will be available
in a separate mailing in the near future. If you have any questions
in the meantime, please contact Dr. Eric van Heugten at (919)
513-1116 or via e-mail at Eric_vanHeugten@ncsu.edu.
Eric van Heugten