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SWINE REPRODUCTION

 

REPRODUCTION                                      PIH-96
PURDUE UNIVERSITY.  COOPERATIVE EXTENSION SERVICE.
   WEST LAFAYETTE, INDIANA
 
             Troubleshooting Swine Reproductive Failure
Authors
   Lawrence Evans, Iowa State University
   Jack Britt, North Carolina State University
   Clyde Kirkbride, South Dakota State University
   Don Levis, University of Nebraska
Reviewers
   John P. Hurtgen, New Freedom, Pennsylvania
   John J. Parrish, University of Wisconsin
   Wayne L. Singleton, Purdue University
 
 
     Some reproductive  failure  occurs  in  all  swine  breeding
   operations,  but  for  practical purposes reproductive failure is
   regarded significant only when production levels fall  below  the
   expected  norm.  These norms may vary from operation to operation
   and are based on such things as percentage  of  animals  cycling,
   conception and farrowing rates, average litter size and number of
   pigs produced per sow  per  year  (Table  1).  The  detection  of
   moderate  rates  of  subfertility  depends upon the observational
   ability of  the  caretaker,  regular  recording  of  reproductive
   events and analysis of reproductive records.
     There is a tendency  to  equate  reproductive  failure  with
   infectious  disease,  but  most problems are not infectious. This
   tendency probably springs from the need to assign the problem  to
   a  tangible  factor  such  as an infectious agent and from public
   awareness of infectious reproductive diseases. Most  reproductive
   problems  have  causes  that involve management practices, nutri-
   tion, environmental effects, toxicoses, genetics and disease con-
   ditions.   Solving  reproductive  problems  requires  a  thorough
   knowledge of the breeding herd management and the collection  and
   analysis  of  pertinent  objective  data  (Table  2). This may be
   followed by submission of appropriate  samples  to  a  diagnostic
   laboratory.  Many  problems  defy  an  exact laboratory diagnosis
   because the causative agent may no longer be present or the prob-
   lem  may  have  been related to prior management or environmental
   factors.
     It is often practical to categorize the reproductive problem
   into  one  or more areas so that specific investigations or tests
   can be applied. Table 3 shows the more common reproductive  signs
   or  complaints  concerning swine reproduction.  Bars indicate the
   relative importance of the female or the male to  each  of  these
   reproductive  problems.  Each  category will be discussed in this
   fact sheet with reference to some  known  causes  and  diagnostic
   procedures.
 
Anestrus
     Gilts. Common complaints with  gilts  are  delayed  puberty,
   silent  estrus  and  anestrus  after  a few heats. These problems
   often are related to modern housing and are influenced  by  breed
   and  age  of the gilts, the season, whether a boar is present and
   to some extent the duration of daylight or artificial lighting.
     Landrace and Large White breeds  tend  to  cycle  better  in
   enclosed facilities and at an earlier age than most other breeds.
   It is stock from herds that have been  shown  to  reproduce  well
   under  management  conditions  similar  to those intended for the
   animals purchased. About 80% to 85% of the gilts should be  show-
   ing  regular  cycles by 7 to 8 months of age, but this percentage
   may be much lower in the summer and fall months. This  percentage
   will not increase significantly for gilts kept beyond 9 months of
   age. Thus, it is not genetically or economically  sound  to  keep
   noncyclic gilts beyond 9 months of age.
     Gilts that are kept in an  enclosed  facility,  isolated  or
   tethered are older when reaching puberty than are gilts kept out-
   side. When gilts  are  housed  in  enclosed  facilities,  smaller
   numbers  per  pen (8 to 12) are better than larger numbers. It is
   best to provide 8 to 10 hours of daylight or artificial light per
   day  and 20 sq ft floor space per animal. Longer day lengths will
   decrease the proportion of gilts cycling.  Moving  gilts  to  new
   pens or to outside housing and exposure to adult boars often will
   stimulate heat in a number of the noncycling gilts  (See  PIH-89,
   Managing the Gilt Pool).
 
Table 1. Expected norms for reproductive performance.
   _________________________________________________________________
   Gilts cycling by 7 months                     75% to 80%
   Weaned sows cycling by 1 week-1st litter      70% to 75%
      -older                                     80% to 85%
   First service farrowing rate-gilts            80% to 85%
      -weaned sows                               85% to 90%
   Litter size-total                             10 to 13
      -born alive                                9 to 12
   Boar, rested for 1 week:
      -ejaculate volume                          150 to 300 ml
      -sperm concentration                       200 to 300 x 106/ml
   Boar fertility-sows that farrow from
      matings to that boar                       80% to 90%
   Sows diagnosed pregnant that
      subsequently farrow                        95%
   _________________________________________________________________
  Since undetected heats often are mistaken for anestrus, heat
   detection methods should be evaluated. Tests for estrus should be
   conducted at least once daily with the aid of a mature boar. Each
   female  must have sufficient time for behavioral interaction with
   the boar either by moving the boar from female to  female  or  by
   moving females past the boar's pen. With the latter method, immo-
   bilization is usually seen in sows or gilts in estrus. The  care-
   taker may assist in detecting estrus by applying back pressure to
   the females as they interact with the boar.  Continuous  exposure
   of  the  gilt  to  boar  stimuli decreases the efficiency of this
   method because the interaction between the animals  becomes  less
   intense  over  time. Electronic devices which have vaginal probes
   have been used successfully  for  detecting  estrus  but  require
   additional labor.
     Gilts should be examined closely for underdeveloped external
   genitalia.  These  often  are heavily muscled, lean animals which
   have delayed puberty and, because this is a heritable  condition,
   replacement gilts should not be selected from these animals.
 
Table 2. Data useful in identifying reproductive problems.
   _________________________________________________________________
Number of times each boar is used weekly.
   Conception and (or) farrowing rates for each group of sows.
   Percentage of gilts bred by 8 months of age.
   Percentage of sows rebred by 1 week after weaning.
   Percentage of sows diagnosed pregnant that subsequently farrow.
   Average litter size, born alive, mummies, and stillborns
     for each group of sows.
   Culling rate after weaning:
      % 1st litter
      % 2nd litter
      % Older
   Estimates of feed intake during gestation and lactation.
   _________________________________________________________________
 
Table 3. Signs of reproductive failure.
   _________________________________________________________________
                              Female suspect         Male suspect
Anestrus
   Failure to mate
   Bleeding at mating
   Repeat breedings
   Abortions
   Mummies
   Stillbirths
   Fewer pigs per litter
   Pregnant sows that
     fail to farrow
   _________________________________________________________________
   Importance:                Primary      Shared      Little
   _____________________________________________________________
     Weaned Sows. A common cause of anestrus in  weaned  sows  is
   insufficient  energy  or protein intake during lactation. This is
   particularly important in sows weaning their first  litters.  The
   frequency of feeding, the design of the feeders (large enough for
   sows) and waterers, and the  nutrients  in  the  feed  should  be
   evaluated. There may be a need to add energy or increase the pro-
   tein in the lactation diet when  feed  intake  is  low.  Improper
   feeding  which leads to excessive weight loss during lactation or
   insufficient weight gain during pregnancy are  the  primary  con-
   siderations  when anestrus occurs following weaning.  Conversely,
   excessive feed intake during  gestation  (overweight  sows)  will
   lead  to  decreased  feed  intake  during  lactation resulting in
   severe weight loss and sometimes anestrus after weaning.
     The length of lactation also influences return of heat. Sows
   with  short  lactations,  particularly  if less than 21 days, may
   require more time to cycle after weaning. There  is  evidence  to
   suggest  that weaning the heaviest pigs in the litter at least 48
   hours early  will  improve  cycling  performance,  especially  in
   first-litter sows.
     The stress of grouping sows and withholding feed after wean-
   ing  will  lengthen  the  average  interval  to estrus. Thin sows
   should be fed 6 to 8 lb of the gestation diet for  at  least  the
   first  week after weaning. Housing sows in crates or small groups
   may increase the percentage of sows that cycle  early.   Exposure
   to a mature boar, either in adjacent pens or by daily movement of
   the boar among the sows, also will  stimulate  early  cycling  in
   postweaned  sows.  Mixing 3 or 4 sows with the boar for the first
   48 hours after weaning reduces fighting among sows  and  provides
   boar stimulus to initiate cycles.
     The summer and fall months are periods of reduced cycling in
   sows.  The  effect of this is minimal if the previously mentioned
   practices are utilized and good heat detection methods  are  fol-
   lowed.
     The diagnosis of anestrous problems  should  be  based  upon
   heat  detection and breeding records. Eighty percent of the gilts
   should be cycling regularly by 8 months of age, or an average  of
   4%  of  the gilts of that age should be in heat each day. Between
   85% to 90% of the sows should have cycled  within  the  first  10
   days following weaning. Estrous detection methods and frequencies
   should be checked closely to assure proper  procedures  are  fol-
   lowed. Other diagnostic procedures might include slaughter exami-
   nations or obtaining serum progesterone levels  to  determine  if
   estrus has been missed.
 
Failure To Mate
     Male refusal. Boars or sows may refuse to mate  even  though
   the  female  is  showing signs of estrus. Usually this is a boar-
   oriented problem.  Insufficient sexual behavior by the  boar  may
   be caused by immaturity, lack of proper sexual experience, genet-
   ics, overuse, over-conditioning or pain associated with breeding.
     Normally young boars begin aggressive mating behavior  by  5
   to  6  months  of age.  Those that are not sexually active by 7.5
   months are problem boars. Rarely is this  problem  related  to  a
   deficiency  of  male hormone; consequently, hormone therapy gives
   poor results. More often, the problem can be traced to a lack  of
   breeding  experience  or  to the boar's ancestry. Providing young
   boars with sexual experience through observation and  interaction
   with compatible males and females is the preferred therapy. Boars
   that are unresponsive to this experience should be culled.
     Experienced  boars  may  have  periods  of  reduced  libido.
   Overuse,  heat stress, over-conditioning and old age are possible
   causes for reduced libido, but pain associated with  breeding  is
   the  most  common  cause of abated libido. Pain from feet, leg or
   back lesions caused by injury or disease is accentuated by mount-
   ing  and  may  inhibit  sexual desire in the male. Lesions of the
   penis or prepuce also may cause sufficient pain to inhibit sexual
   activity.
     Some boars may mount sows but  be  unable  or  unwilling  to
   enter  the  female. This may be due to pain from skeletal disease
   or to abated libido occurring as the boar passes his prime age of
   sexual  drive. Other boars may develop the habit of diverting the
   penis into their preputial diverticulum. This  condition  can  be
   corrected  by  surgery,  but  large diverticula are heritable and
   predispose the boar to this problem.
     Virgin boars that fail to mate should be examined for abnor-
   malities  of the penis, including fibrous tags (persistent frenu-
   lum), incomplete erection or short penis syndrome. Usually  these
   boars  can expose only the spiral tip of the penis while attempt-
   ing to mate. These are heritable conditions, and  affected  boars
   should  not  be  used  for  breeding stock production. Boars with
   fibrous tags often can be salvaged for commercial use with surgi-
   cal correction.
     The diagnosis of these boar problems is based on good obser-
   vations,  radiographs  to detect bone disease, and, occasionally,
   examination of a boar under anesthesia  for  penis  or  preputial
   problems.
     Female refusal. Sows or gilts  in  estrus  may  occasionally
   refuse  a boar, particularly a young boar. For this reason mature
   boars are better teasers.  Gilts  that  aggressively  refuse  the
   male  should  be  culled  as undesirable genetic stock. Shy gilts
   that simply avoid the boar when in estrus may breed normally with
   additional  boar  experience.  However,  it  is more desirable to
   select replacement gilts that readily express estrous behavior at
   an  early age. Sows or gilts that object to entry of the boar may
   have cervical, vaginal or urethral damage from prior breeding  or
   farrowing.
 
Bleeding at Mating
     Hemospermia (blood in the semen) has been clinically associ-
   ated  with  reduced  conception  rates.  Bleeding boars should be
   examined for trauma of the shaft and spiral part  of  the  penis.
   This  occurs  commonly from homosexual activity and with pen mat-
   ing, when boars have difficulty entering sows.  Sexual  rest  for
   two  weeks  and elimination of the cause are necessary for return
   to  normal  function.  Bite  wounds  to  the  penis  usually  are
   inflicted  by  an  intruding  sow or boar during breeding. One or
   more boars in the pen may be injured.  Affected boars  should  be
   given  antibiotics for 10 days and sexual rest for 3 weeks. After
   this time, the boar  should  be  test-mated  and  examined  under
   anesthesia if bleeding still occurs.
     After breeding, virgin gilts and some sows  may  bleed  from
   cervical,  vaginal  or  urethral injury. Most recover by the next
   estrous period.
     The diagnosis of a bleeding problem is made  by  observation
   at  mating,  vaginal examination of the female and, occasionally,
   examination of the boar under anesthesia.
 
Repeat Breedings
     When repeat breeding is a herd problem,  it  is  helpful  to
   determine  the percentage of repeat breeding sows, the percentage
   of sows with return intervals of 24 days or more, and the service
   records of individual boars.
     Repeat breedings, regular intervals. When more than  15%  of
   the  bred  sows  return to estrus within 18 to 23 days, both male
   and female infertility must be investigated.  Primary  considera-
   tions are boar infertility and poor timing of matings that result
   in lower conception rates. Very low conception rates often  indi-
   cate  male  infertility.  Diagnostic efforts should include semen
   quality examination, observation  of  boar  behavior  and  mating
   ability and a review of boar management and use.
     Boars used excessively (more than 7 matings per week)  on  a
   continual  basis  may  have  reduced  fertility. Therefore, boars
   should be rotated every 24 hours during heavy pen mating usage (2
   boars  for  every 4 to 6 sows weaned per week).  When hand-mating
   or artificial insemination (AI) is employed, heat  detection  and
   breeding  times are important. Best fertility occurs when females
   are bred 10 to 12 hours before ovulation. However,  the  interval
   from the start of heat to ovulation is variable. That interval is
   estimated to be 30 to 36 hours in gilts and 38  to  44  hours  in
   sows,  but  the detection of first signs of heat may be difficult
   or delayed. For this reason, two services  per  heat  period  are
   recommended.  Table  4  gives a suggested breeding schedule based
   upon the frequency of heat detection checks.
 
Table 4. Breeding schedule for hand-mating (hours after detecting
   heat).
   _________________________________________________________________
                                   Frequency of heat detection
                       _____________________________________________
   Type of female             once daily               twice daily
   _________________________________________________________________
   Gilt                         0 & 24                   12 & 24
   Sow                          12 & 36                  24 & 36
   _________________________________________________________________
     Double-mating increases  conception  rates  by  10%  to  30%
   because  it  increases  the  chance  of  breeding near ovulation.
   Nearly all the sows and at least 70% of  the  gilts  should  have
   double services if adequate heat detection methods are used.
     Boars exposed to high  environmental  temperatures  (greater
   than  90o   F)  for  several days may suffer reduced fertility for
   several weeks. Providing shade and water sprinklers for the  boar
   during  hot  weather  reduces  heat  stress and semen damage (see
   PIH-87, Cooling Swine). Likewise, acute  systemic  diseases  that
   cause  a  high  fever  in  the  boar can cause semen damage. Con-
   versely, boars exposed to cold stress for several days during the
   winter  can  be  rendered  infertile  or  subfertile  for several
   months.
     Evaluation of semen samples will detect  the  infertile  and
   some  subfertile  boars.  Other  subfertile boars can be detected
   only by evaluating the breeding record (farrowing rate and litter
   size) of individual boars.
     When an individual sow or gilt returns to estrus  repeatedly
   at  regular  intervals after breeding, lesions of the oviducts or
   uterus should be suspected. The reproductive tract can  be  exam-
   ined at slaughter or by surgery.
     Another cause of reduced fertility in the female is  uterine
   infection.  Bacteria may be introduced into the uterus at farrow-
   ing or at breeding. Most of the affected sows  return  to  normal
   fertility  by  the  next  estrus  unless  a chronic urinary tract
   infection exists. The sow with a urinary tract infection may have
   bloody  urine.  A  few  animals  may  have  a  noticeable vaginal
   discharge at approximately 16 to 17 days after breeding  as  they
   abort  the  pregnancy. The boar with preputial infection often is
   responsible for spreading infection among females.
     Parvovirus is the most prevalent viral agent  involved  with
   infertility.  It  rarely  causes  repeat breeding alone but often
   results in mummification of fetuses. It  occurs  much  more  fre-
   quently in gilts than in sows.
     Eperthrozoonosis (Epy) has been suggested but not proven  to
   be a cause of infertility in the sow and gilt. This is most often
   diagnosed as a problem in the fall.  It  is  theorized  that  the
   decrease  in  fertility during late summer is analogous to a sea-
   sonal anestrus  in  other  species  rather  than  the  effect  of
   eperthrozoonosis.
     Repeat breeding with a delayed return to  estrus.  Normally,
   the  incidence of delayed (24 days or more) return to estrus fol-
   lowing breeding is rarely higher than 3% to 4%.  This  percentage
   may  increase  by 3 to 4 times for females mated in July, August,
   September and October and when bred females are moved  and  mixed
   during early pregnancy (up to 4 weeks postbreeding).
     Delayed return to estrus suggests a loss of early pregnancy.
   Uterine infections caused by viral or bacterial agents may be the
   cause. Pseudorabies and parvovirus  are  viral  agents  that  may
   cause  this  problem. Bacterial agents associated with lower con-
   ception rates and delayed return to heat include a  wide  variety
   of  organisms.  Staphylococcus  species  (spp.), alpha- and beta-
   hemolytic Streptococcus spp., Escherichia coli, Pasteurella  mul-
   tocida,  Actinobacillus  spp.  and  Eubacterium suis are commonly
   present in the vagina and occasionally are  introduced  into  the
   uterus. A chronic leptospirosis infection may cause repeat breed-
   ing in sows, but abortions are usually seen in other sows in  the
   herd.  The  involvement of Mycoplasma spp. and Ureaplasma spp. in
   swine infertility is questionable.
     Bacterial infections may  be  prevalent  in  the  uterus  or
   vagina  due  to  contamination  from  the farrowing barn, bladder
   infections or breeding.  Sanitation in the farrowing and breeding
   facilities is extremely important when attempting to curtail this
   problem. Removal of manure from behind sows in individual stalls,
   on a daily basis, may be helpful.
     Diagnostic efforts in repeat  breeding  problems  should  be
   directed to:
1.   Boar fertility and use.
2.   Bacterial culturing of vaginal discharge.
3.   Serological (blood) tests for pseudorabies  and  parvovirus.
        Interpretation  of  the  test  results  is  difficult unless
        results of a prebreeding test also are available.
4.   Diagnostic procedures for early pregnancy detection, includ-
        ing  blood  tests  for  progesterone or estrone sulfate, and
        ultrasonic tests.
5.   Examination of reproductive tracts collected  at  slaughter.
        Bacterial culturing of these tracts may not be satisfactory
     because of contamination of the organs with  scalding  water
        and urine during slaughter procedures.
 
Abortions
     An abortion rate of 1% to 2% is regarded as  normal  in  the
   swine  breeding  herd.   The number increases slightly during the
   fall months.
     When many abortions occur, specimens should be submitted  to
   a  diagnostic laboratory. An exact diagnosis is achieved only 20%
   to 30% of the time.  Abortions are caused by  infectious,  toxic,
   genetic, metabolic, and other factors.
     Infectious agents such as pseudorabies virus,  Streptococcus
   spp.,  E.  coli,  Erysipelothrix  rhusiopathia,  Salmonella spp.,
   Pasteurella spp., and Actinobacillus pleuropneumonia  cause  sys-
   temic  disease,  fever,  and  abortion in 2 to 14 days. They fre-
   quently cause abortion storms. The  disease  condition  currently
   called  Swine Infertility and Respiratory Syndrome (SIRS) or Mys-
   tery Swine Disease normally follows a similar pattern. Sick  sows
   are observed first, followed by abortions and later by stillborn,
   weak pigs and mummies.  Nursing and weaned pigs often  will  have
   pneumonia.  A  viral  agent is the most likely cause. In Europe a
   similar syndrome known as Porcine  Reproductive  and  Respiratory
   Syndrome  (PRRS)  has  been  associated  with a new viral isolate
   named the Lelystad virus. Researchers in the United  States  have
   isolated  a  viral  agent (BIAH-001) responsible for causing SIRS
   which seems to differ antigenically from the Lelystad isolate.
     Leptospirosis  and  brucellosis  usually   cause   abortions
   without prior evidence of systemic disease. Leptospira bratislava
   is  a  recently  investigated  serotype  which  appears   to   be
   widespread  in  swine  herds  and  has been isolated from aborted
   fetuses. Its incidence in abortion storms and swine  reproductive
   failure syndrome is very low. Toxoplasmosis and mycotic infection
   cause sporadic abortions of a similar nature.
     Toxic agents also cause abortions. Carbon monoxide poisoning
   produced  by poorly adjusted or unvented heaters in the farrowing
   house causes late-term abortions without much  evidence  of  sys-
   temic disease in the sow. These aborted pigs have cherry red tis-
   sues. Zearalenone is a mycotoxin produced in  moldy  feeds  which
   has been associated with causing abortions (See PIH-129, Mycotox-
   ins and Swine Performance). Aflatoxin, ergot  and  vomitoxin  are
   agents  produced  by  moldy feed, but they do not generally cause
   abortion. Likewise, nitrates or nitrites in feed  or  water  have
   not been shown to cause abortion or fetal loss in swine.
     Cold stress also can cause abortion in late-term sows.  Usu-
   ally  this  is  caused by inadequate energy intake and acute heat
   loss when bedding is scant or absent. These abortions  may  occur
   during  the  winter when sows are on limited feed and lie on cold
   concrete floors.
     Diagnostic procedures for  determining  causes  of  abortion
   include submission of aborted fetuses and placentae to a diagnos-
   tic laboratory for culture and histologic examination; submission
   of  blood  samples to be tested for pseudorabies, brucellosis and
   leptospirosis; testing feeds for mycotoxins, and  monitoring  the
   environment for carbon monoxide or cold stress.
 
Mummified Fetuses
     Mummified fetuses occur in normal farrowings at a rate of 4%
   to  5%.  These represent fetuses that died in the uterus at 35 to
   90 days gestation without causing sufficient uterine reaction
to result in abortion. Noninfectious causes  of  mummies  include
   placental insufficiency and lethal developmental abnormalities.
     Parvovirus is the most  common  infectious  agent  known  to
   cause  mummification; however, other viruses such as EMC, Entero-
   viruses and the Swine Reproductive Respiratory Syndrome may cause
   mummies  in  the  litter. Parvovirus has been diagnosed most com-
   monly with mummies and hence, has received a great deal of atten-
   tion.
     Infection of the litter with parvovirus must  occur  in  the
   first  70 days of gestation to cause fetal death. Fetuses usually
   vary in age and size at death because the  virus  spreads  slowly
   from  one  fetus to another in the uterus. It occurs in both sows
   and gilts, but most sows have immunity prior to breeding.   Gilts
   raised  in  isolation may not have prebreeding exposure to parvo-
   virus, and they are much more likely to  become  infected  during
   pregnancy.  Gilts  can be tested for immunity (seroconversion) to
   parvovirus prior to the breeding period, and immune  animals  can
   be used for breeding. Exposing the gilts and animals being intro-
   duced to the breeding herd to  boars  and  older  sows  or  their
   manure  generally improve seroconversion rates. Additionally, the
   gilts should develop immunity to other viral agents in the  herd.
   Gilt  herds  which  have been maintained in isolation for disease
   control may rely on prebreeding vaccination for  parvovirus  pro-
   tection.
     Parvovirus can be readily identified in mummified fetuses by
   laboratory examination. This is the most reliable method of diag-
   nosis. Elevated serologic titers  are  not  significant  evidence
   that  parvo caused fetal loss unless blood samples also have been
   taken before breeding and a rise in parvovirus antibodies can  be
   demonstrated in the second sample.
 
Stillbirths
     A stillbirth rate of 6% to 8% is common in farrowing  units.
   This  represents death of the fetus just before or during farrow-
   ing. These rates increase rather dramatically as  the  sow  ages,
   particularly after 6 litters.
     There are  several  factors  that  contribute  to  increased
   stillbirths. Infections such as leptospirosis or pseudorabies and
   carbon monoxide toxicity may increase stillbirths,  but  abortion
   will be present in other sows if these agents are present.
     Overweight sows and gilts or those subjected to heat  stress
   have  higher  stillbirth  rates. Likewise, sows or gilts that are
   uneasy in the farrowing facilities or are disturbed  during  far-
   rowing  are  likely  to  have  slower farrowings with more still-
   births. Low blood glucose, hemoglobin or calcium may  reduce  the
   responsiveness  of  the uterine muscles and cause delayed or pro-
   longed labor resulting in stillbirths.
     Sows with large litters and prolonged parturition  and  sows
   with  small  litters,  but large pigs, have a higher incidence of
   stillborn.  Gilts  with  small  pelvic  size  also  have   higher
   stillborn rates. Stillbirths can be significantly reduced if far-
   rowings are supervised and sows with prolonged labor are  treated
   with  oxytocin. Supervision of farrowings has been facilitated by
   synchronized farrowings with prostaglandin and oxytocin.
     Diagnosis of the cause of stillbirth  involves  testing  for
   infectious  agents, carbon monoxide toxicity, altered blood chem-
   istry, observing the farrowing process  to  determine  if  still-
   births are related to prolonged labor and determining the age and
   parity of problem sows.
 
Small Litters
     Small litters are considered significant when more than  15%
   of  sows farrow fewer than 7 pigs. Major factors affecting litter
   size are breed and heterosis  of  the  dam,  number  of  previous
   litters  (parity  of  the  sow), duration of prior lactation, and
   adequacy of male services.
     It is obvious that breed  and  heterosis  of  the  dam  will
   influence the number of pigs farrowed. Selecting gilts from prol-
   ific dam and sire breed  lines  will  generally  increase  litter
   size.
     Litter size generally increases with each parity beyond  the
   second  litter, but litter size weaned is generally reduced after
   6 litters. To maintain maximum litter size and replacement  effi-
   ciency,  a  herd  should  be  approximately  25% to 30% first and
   second litter sows.
     Breeding sows at less than 21 days after farrowing will gen-
   erally  reduce  litter size. Litter size tends to increase as the
   interval from previous farrowing is increased,  up  to  about  35
   days.  However,  total  pigs  per  sow per year are significantly
   higher with the shorter lactation period. The appropriate weaning
   age  for a given production unit will depend upon nursery manage-
   ment and the reproductive response of the weaned sows.
     Inadequate boar coverage also will decrease  average  litter
   size.  Subfertile  or  overused  boars  can  cause small litters.
   Improper timing at mating, breeding too early or too  late,  will
   cause individual sows to recycle or have small litters. Poor con-
   ception rates in pen or pasture breeding will accentuate the boar
   usage  leading  to  overusage, small litters, and increased recy-
   cling. With handmating, the boar/sow ratio recommended is 1  boar
   per 2 sows weaned weekly. This results in approximately 4 matings
   per week for each boar.  Pasture and pen mating ratios should  be
   about  1  boar to each 2 to 3 sows weaned per week with the boars
   working in groups of 2 in a pen of 8 to 12  sows  and  another  2
   boars rotated in their place at 24 hour intervals. This maximizes
   boar usage through less  competition  but  minimizes  overuse  of
   individual boars.
     Diagnostic procedures for determining the cause  of  reduced
   litter size in the herd include assessing boar fertility and use,
   genetic factors, breeding practices and average parity of the sow
   herd.  A  secondary approach is determining the possible presence
   in the herd of infectious agents that  interfere  with  reproduc-
   tion.
 
Pregnant Sows That Fail to Farrow
     Occasionally, sows or gilts that were presumed or  diagnosed
   pregnant fail to farrow. Viral infections that cause death of the
   entire litter during early gestation can result in sows that look
   pregnant but never farrow. Parvovirus introduced at 30 to 60 days
   of gestation is a likely cause.
     Misdiagnosis of pregnancy  occurs  with  variable  frequency
   depending  upon  the  method used and the skill of the diagnosti-
   cian. Generally, sows that are incorrectly called pregnant (false
   positive)  can  be  identified by good heat detection methods but
   anestrus during the late summer and fall months may mask the mis-
   diagnosis.
     Pseudopregnancy in the sow occurs when  noncycling  sows  or
   gilts are exposed to estrogenic agents such as zearalenone (some-
   times produced in moldy feed).  Concentrations of  4  to  10  ppm
   zearalenone  will  cause  anestrus.  These sows fail to return to
   estrus, react questionably to pregnancy testing dev-
 
ices that detect fluid  in  the  uterus  and  have  some  mammary
   development.  Pseudopregnancy  also  may occur more frequently in
   sows bred in early fall.
     Procedures for diagnosis of failure to farrow  are  directed
   to assessments of pregnancy detection procedures, the possibility
   of moldy feed and infectious agents. Examination of  reproductive
   tracts  at  slaughter may reveal uteri full of mummified fetuses.
   These should be tested for parvovirus. Sows  with  empty  tracts,
   which  have  large  pale, mature corpora lutea but no old corpora
   lutea or new large follicles, and a thickened  congested  uterine
   lining  suggest pseudopregnancy. If available, feed from previous
   periods should be tested for zearalenone.
 
Summary
     The first step in investigating swine  reproductive  failure
   is  recognition  of the problem with a thorough review of produc-
   tion records. Many times several problems  exist  simultaneously,
   but  the  attention directed toward these problems often improves
   the reproductive management and productivity even  when  a  diag-
   nosis has not been confirmed.
Other recommended PIH fact sheets:
   PIH-1     Management of the Boar
   PIH-8     Managing Sows and Gilts for Efficient Reproduction
   PIH-59    Infectious Swine Reproductive Diseases
   PIH-74    Management of Developing Gilts and Boars
   PIH-87    Cooling Swine
   PIH-89    Managing the Gilt Pool
   PIH-129   Mycotoxins and Swine Performance
 
REV 12/92 (7M)
   ______________________________________________
Cooperative Extension Work in  Agriculture  and  Home  Economics,
   State  of Indiana, Purdue University and U.S. Department of Agri-
   culture Cooperating. H.A. Wadsworth,  Director,  West  Lafayette,
   IN. Issued in furtherance of the Acts of May 8 and June 30, 1914.
   It is the policy of the Cooperative Extension Service  of  Purdue
   University  that  all  persons  shall  have equal opportunity and
                access to our programs and facilities.

 

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