HERD MANAGEMENT                                   PIH-8


         Managing Sows and Gilts for Efficient Reproduction

John R. Diehl, Clemson University
James R. Danion, Auburn, University
Leif H. Thompson, University of Illinois

Tro V. Bui, Cornell University
Wray and Nancy Garrison, Lovell, Wyoming
Gene and Bev Gentry, Farmington, Iowa
Duane Miksch, University of Kentucky

     Every producer should give the highest priority  to  manage-
ment of females in the breeding herd to achieve maximum reproduc-
tive efficiency. Good reproductive management will pay  dividends
by  increasing the number of live pigs farrowed.  Similarly, good
nutritional management can improve the size and viability of pigs
at birth. The more live pigs farrowed, the greater the likelihood
that there will be more at market weight.  The  purpose  of  this
fact  sheet  is  to identify important points of reference in the
reproductive life of the sow which respond to good management  by
yielding additional live pigs at farrowing.

Prebreeding Management

     Gilt Management. Selection of  females  for  replacement  is
only  the  start of managing for highest reproductive efficiency.
Gilts should be selected from family lines  which  have  superior
mothering  ability  (refer  to  PIH-27). A good indication of the
female's ability to function normally is whether she  will  start
coming  into  heat  at  an  early age. Gilts may start cycling as
early as 5 mo. of  age  (Table  1).  The  general  recommendation
regarding  age at first breeding has been to wait until the third
heat to take advantage of any  increase  in  ovulation  rate.  In
swine  units where the breeding groups are kept inside, gilts not
bred at first heat may stop cycling. It is recommended that gilts
not  reaching puberty by 9 mo. of age be culled from the breeding
herd.  The decision to breed on first or  third  heat  should  be
based  on  more factors than the possibility of increasing ovula-
tion rate by one or two eggs.  Fluctuating prices for feed, labor
and facilities, salvage values of breeding stock, market expecta-
tions, etc., can create temporary situations that make it  unpro-
fitable  to  wait  until 7 or 8 mo. of age before breeding gilts.
But be aware that there will likely be fewer rebreeding and  lac-
tation  failure  problems if gilts are first bred at their second
or third estrus.


Table 1. Normal age range of puberty, estrus and ovulation.

Age at puberty                      5-8 mo.
Weight at puberty                   150-250 lb.
Duration of estrus                  5 da. (2 avg.)
Length of estrous cycle             18-24 da. (20-21 avg.)
Weaning to estrus                   3-8 da. (5 avg.)
Time of ovulation                   40 hr. (from onset of estrus)


     Mixing or regrouping gilts (with boar contact) at about  160
days  of  age  can  be beneficial and help to advance the date of
first estrus, especially when they're not raised  in  dirt  lots.
Those  not bred after 3 wk. of heat checking should be remixed to
stimulate anestrus females. This may help synchronize  the  first
heat and, to a lesser degree, the second heat.

     Seasonal differences in age at first heat are  a  widespread
problem.  In general, research has indicated that fall-born gilts
reach puberty at a lighter weight  and  at  a  younger  age  than
spring-born  gilts.  Boar  exposure  decreased  age and weight at
puberty in spring gilts but not in fall-born gilts. In a Canadian
report, an average of 9.7% of the gilts weighing 195-200 lb. that
were slaughtered from June through September had reached puberty;
whereas  an  average  of  22.8% of gilts slaughtered from January
through June had attained puberty.

     Anestrous conditions (absence of standing heat) may  be  the
result of a number of conditions:

     1.   Faulty heat detection

     2.   Hot weather stress

     3.   Silent heat (ovulation with no visible sign of heat)

     4.   Sickness

     5.   Nutrition (lack of protein and/or energy)

     6.   Social stress

     Heat Detection. Good systematic heat detection  is  critical
for  achieving  a  high  pregnancy rate and faulty detection is a
major cause of problems. Heat is the time the female accepts  the
male  for mating. A good method to detect heat is to bring a boar
into a pen of females. The producer then should apply back  pres-
sure  to  each  female  in  the  presence of the boar. Nearly all
females that are in ``standing heat'' will allow the man  to  sit
on  their  back.  Most  sows  or  gilts  will respond by standing
solidly and  attempting  to  stiffen  their  ears  erect  (called
``popping-their-ears'').  If females do not stand solidly and pop
their ears,they are not in heat. Particularly in gilts, the vulva
may be swollen and/or nervousness may be noticed before and after
standing heat.

     Effect of High Temperature. High temperature (above  85  F.)
will  delay  or  prevent the occurrence of heat, reduce ovulation
rate and increase early embryonic deaths. Michigan studies showed
that  gilts  exposed  to  104 F. for 2 hours daily from 1-13 days
postbreeding had reduced embryo survival by as  much  as  35-40%.
Other  studies at Illinois and Oklahoma show similar results from
heat stress. The number of boars used and  females  kept  in  the
breeding  pool should be adjusted especially in the hot mo. based
on records of conception rates. See Table 2 for suggested adjust-
ment  factors.  Animals also suffer similar stress from high body
temperature when they get sick and have a fever.  More  variation
in  the  length  of  standing  heat  can  be  expected due to hot
weather. Not only does temperature have detrimental effects,  but
decreasing length of days and relative humidity can also interact
to multiply the problems a producer may encounter during the sum-
mer  mo..  An individual producer must do a good job of selecting
replacement breeding  stock  that  are  reproductively  efficient
under  his  management  system  to  minimize  the effects of heat


Table 2.  Suggested  coefficients  to  determine  the  number  of
females to be bred each month.


Month                                                 Coefficient

January                                                  1.25
February                                                 1.28
March                                                    1.35
April                                                    1.43
May                                                      1.52
June                                                     1.64
July                                                     1.69
August                                                   1.82
September                                                1.52
October                                                  1.35
November                                                 1.30
December                                                 1.25


Numbers to breed each month =  (number  of  farrowing  stalls)  x

     The effect of heat on the boar's  reproductive  capacity  is
decreased  sex drive, lowered sperm output and lowered sperm fer-
tility. If rectal temperature increases as little as 1 F. for  72
hours,  sperm  production is decreased by 70% or more. Once sperm
production is affected, normal sperm production is  not  attained
for  at least 4-6 wk.. See Pork Industry Handbook Fact Sheet PIH-
87, Cooling Swine.

     Keep group sizes to 15  or  less  if  possible  to  minimize
peck-order  fighting  and  help  insure  that all females receive
their day's ration of feed. The  use  of  individual  stalls  may
prove  to  be  economically  feasible to cut down social stresses
associated with the breeding herd.

     Sow Management. Sows occasionally come into heat while their
litter  is still nursing especially if lactation lasts beyond 5-6
wk. If a sow does express heat while she  is  nursing,  she  most
likely will not return to heat within 3-7 days postweaning.

     Selection for sows that do cycle within 7  days  postweaning
is  very important to keep management schedules running smoothly.
A number of producers use early return to heat as  a  prime  con-
sideration  for  retaining  sows  in the breeding herd. This cri-
terion automatically selects a  female  capable  of  successfully
contending  with  the stresses of living in a particular environ-
ment. If a sow fails to conceive within 28 days postweaning,  she
should  be  culled.  This  is enough time for her to have been in
estrus twice. With each 21-day delay, the sow must produce one to
two  extra  pigs  just to pay for the extra labor and feed. Simi-
larly, if cycling gilts  do  not  conceive  after  three  estrous
cycles, they should be culled so as not to increase the number of
``hard breeders'' in future generations.

     If adequate nursery facilities  are  available,  weaning  is
recommended  at 3-4 wk. of age so the sow can be returned to pro-
duction as soon as possible.  Results of one study  conducted  in
England  show a decrease of about three pigs per litter when sows
were weaned and bred before 21 days of lactation.  Weaning groups
of  sows  at an average litter age of 3 1/2 wk. is usually a good
practice to follow.

     If postweaning scours are a problem,  postpone  weaning  for
another week or more; then leave the litter in the farrowing area
an additional week. This will extend scours  protection  provided
by  the  sow's milk. An extra week will allow additional time for
the pigs to get started eating dry feed. Sows in  thin  condition
should  be  on  a high plane of nutrition and in a weight-gaining
status before breeding. This will assure maximum  ovulation  rate
as far as nutrient intake is concerned.

     Synchronization of heat  in  sows  is  a  relatively  simple
matter  when  pigs  are  weaned  from a group of sows at the same
time. A high proportion of sows that are in good physical  condi-
tion  will  begin  to come into heat within 3-7 days postweaning.
Adequate boar power is essential for synchronization of postwean-
ing  heat  to  be effective. If your sows do not respond, analyze
your production system and try to determine the cause.

     Herd Health. Abortions, mummified fetuses,  stillbirths  and
irregular  estrous  cycles  are  indicative  of potential disease
problems. Pseudorabies, parvovirus and enterovirus  may  also  be
responsible  for  the  occurrence of mummies. There are no treat-
ments for any of the viral  diseases.  Consult  with  your  swine
veterinary  practitioner  for  vaccines  effective  in preventing
viral diseases.  Leptospirosis and brucellosis continue to  cause
losses.  Their  symptoms  can  be  inconsistent. Irregular cycles
should raise suspicions regarding these infections and  appropri-
ate  vaccination  and  blood  testing can lead to their effective
control. If there is any question about the health status of  the
breeding  herd,  consult with a swine veterinary practitioner and
review your herd health program.

Breeding Management

     The all-important factor in achieving a high conception rate
and  good litter size is to get sperm into the female's reproduc-
tive tract at the time when pregnancy rate and litter  size  will
be  maximized.  Regardless  of  the method of breeding (i.e., pen
mating, hand mating  or  artificial  insemination),  an  adequate
number of live sperm must be in the tract a few hours before ovu-
lation occurs or conception rate and litter size will be reduced.
Figure 1 shows the effect on conception rate of breeding at vari-
ous times in relation to time of ovulation. Notice that when heat
lasts 48 hours a female will ovulate 8-12 hours before the end of
standing heat (37-40 hours after the  onset  of  standing  heat).
When  mating  occurs  too  early or too late, conception rate and
litter size drops very rapidly.

     The general recommendation for optimal breeding is based  on
the  number  of  times  per day a producer checks the females for
signs of standing heat. With once-a-day heat detection, breed the
females each day they will accept a boar. With twice-a-day detec-
tion, breed at 12 and 24 hours after they are first  detected  in
heat.  Heat  detection should always be done in the presence of a
boar to maximize the chances of detecting all possible females in
heat.  This applies specifically to producers using hand breeding
or artificial insemination rather than pen breeding.

     Abnormalities in the estrous  cycle  do  occur.  Gilts  will
sometimes  have less than a two-day heat period. If this happens,
they are most apt to ovulate shortly after going out of heat.  If
short  heats  are a problem, then gilts should be bred as soon as
they are detected in heat and each succeeding 12 hours they  will
stand.  When  the  period  of  male receptivity lasts longer than
three days, chances are females may not conceive; so it is  prob-
ably  a  waste  of  time  and boar power to continue to breed her
after the third day.

     Producers using unobserved (pen) mating must have plenty  of
boar  power available. For each 10 sows use one mature boar (over
1 year of age) per 21-day breeding period. Decrease that ratio to
4-6  sows  for  each young boar (less than 1 year). A sow-to-boar
ratio of 4 to 1 for mature boars and 2 to 1 for  young  boars  is
recommended when sows are weaned in groups. When hand mating, the
mature boar should not breed more than 2 females a day if  he  is
to  be  used  intensively  for more than a couple of days, or the
sperm reserve and/or sex  drive  will  be  decreased.  Artificial
insemination  is  extremely  useful in this situation since it is
possible to breed 10 or more sows with the sperm  harvested  from
one  ejaculate.  See  PIH-64.  Using individual stalls during the
first 30 days of gestation  will  significantly  increase  litter
size  and  possibly  conception  rate  during the late summer and
early fall mo.. They help reduce social stresses  encountered  in
group  housing  and  insure  access  to  feed. This is especially
important for first litter sows and pubertal gilts.

     An additional boost in conception rate and litter  size  can
be  obtained  by  using more than one boar on each female (double
mating). This maximizes the chance that a highly fertile and com-
patible  boar will be used on the female. It is easiest to accom-
plish when using hand mating or artificial insemination. This can
be  done  when pen breeding by rotating boars at least once every
day from pen to pen. Sex drive can be enhanced in boars  by  fre-
quent rotation.

     The labor requirement is lowest for pen  breeding.  However,
in  most  cases  breeding dates are not known, so if one is to be
present during farrowing, a greater amount of time spent  in  the
farrowing  house is required. Less is known about the mating per-
formance of the males or females;  therefore,  problems  such  as
origin  of  blood  in  semen and inability to couple properly and
others are more likely to occur without being noticed. This makes
it  more difficult to keep accurate records of individual perfor-

     Pregnancy Detection. Electronic  pregnancy  diagnosis  is  a
reality.  With  the ultrasonic detectors, a producer can find out
with a 90-95% accuracy how many females  have  settled  early  in
gestation.  These  machines  are  most accurate and give the best
return per dollar invested when they are used between  30  to  45
days  after  breeding.  The economic advantage and accuracy drops
off rapidly after 45 days.

     If bred females are observed for return to estrus  at  18-25
days  following mating, electronic heat detectors are not needed.
Most producers do not remove open  females  from  gestation  pens
before  90 days. Assuming feed costs amount to $0.35-0.50/day for
open or pregnant females, and that  an  average  of  10%  of  all
females bred will not conceive, it costs about $30 to maintain an
open female between days 30-90 postbreeding. Therefore,  a  preg-
nant  sow  must  produce  3  extra pigs just to pay for each open
female's feed cost.  On  this  basis  a  producer  farrowing  300
litters  per  year can pay for a pregnancy testing machine within
two years.

     Nutrition. It is important that brood sows and gilts get the
proper  amount  of nutrients for successful reproduction. Feeding
in excess is not  only  wasteful  and  costly  but  may  increase
embryonic  mortality. A limit-feeding system using balanced, for-
tified diets is recommended. It insures that each  sow  gets  her
daily requirements of nutrients without consuming excess energy.

     As a rule of thumb, 4 lb. of a balanced ration will  provide
adequate  protein  and energy. During cold weather, an additional
pound or two of feed depending on the type of housing, may  prove
beneficial,  especially for bred gilts and thin sows. With limit-
feeding it is extremely important that each sow gets her level of
feed  and  no  more.  One of the following systems may be used to
restrict energy  intake  of  gestating  females-daily  individual
limit feeding or interval feeding.

     The daily feeding of a limited amount to each individual  is
the  most  popular  system, and its success is based on having an
adequate  number  of  feeding  stalls  or  space  for  individual
animals.  The  individual  stall  is best because it prevents the
``boss sows'' from taking feed from slower eating or timid  sows.
However, individual feeding takes more labor if it is not mechan-
ized. Self- feeding for given intervals (1  day  every  3rd  day)
takes  less labor but is the least acceptable method for two rea-
sons: (1) it costs more to maintain sows and (2) it is very  dif-
ficult  to  control  feed  intake.  Constipation  problems can be
minimized by feeding a bulky ration for several days prior to the
expected  day  of  farrowing.  Occasionally,  a sow may need some
exercise. Remove all feed the day of farrowing.

     All animals are territorial and therefore like to have  some
space  identifiable  as  their  own.  Use of individual stalls or
maintaining  small  groups,  especially  during  early  gestation
(through  day  30), provides for this need. Some breeds appear to
adapt better to stalls than others, Yorkshire and Landrace, while
the Hampshire breed is one considered best adapted to pen or even
outside lots. If gestating females are group housed, keep them in
as  small a group as possible and separate gilts and first litter
gilts from older and fat sows. Comfort and  contentment  of  bred
females  is  important for efficient reproduction. The above fac-
tors should be considered to achieve maximum  profitability  from
the breeding herd.

     Introducing New Breeding Stock. Many producers bringing  new
breeding  stock  into  their  operation  create  situations  that
increase herd health problems.  This is done when new animals are
not  properly  quarantined.  All  new  breeding  stock  should be
totally isolated for 30  days.  Retesting  for  certain  diseases
should  be done in consultation with your veterinarian. Then dur-
ing the next 30 days, start  commingling  by  direct  contact  or
reciprocal  feeding  of fecal material from the new livestock and
open females only. In this way the new open females will be  able
to  build an immunity to any new organisms they may encounter. If
new boars or gilts have a new virus and it is transmitted to bred
females,  all  the  signs of infertility mentioned previously may
show up.  In addition, near the end of the initial 30-day  isola-
tion, test mate boars to females to be culled to observe breeding
ability. Use cull females so that if new  organisms  are  present
the  effect will not be costly. Commercial producers can purchase
females or use their own farm-raised females for replacements and
upgrade  their  herd  by bringing in new boars or semen. Purebred
females should come from a single source at  any  given  time  to
minimize potential health problems.

Farrowing Management

     Be present when sows farrow, but do not offer any assistance
unless  necessary.   Keep  sows  as  comfortable as possible. The
average interval between births is  approximately  15-20  minutes
unless a problem develops. Producers with more experience in han-
dling farrowing problems may assist the sow in  trouble  (greater
than  25-30 minutes between births). If help is unavailable, con-
sult a veterinarian as soon as  possible.  Keep  the  pen  clean,
remove  all  afterbirth and supply supplemental heat for the baby
pigs. Make sure sows have  plenty  of  fresh  water.  Check  them
closely  and be sure they remain in good health and properly care
for their pigs. If breeding dates and the average length of  ges-
tation  for  sows  and  gilts  is known, you may wish to consider
inducing farrowing with Lutalyse or other prostaglandins to shor-
ten  the  time  required for farrowing observation and facilitate
crossfostering of large with small litters. Close observation  is
recommended to allow attention to be given when problems occur.


     Records in swine production are essential. To keep  accurate
records,  hogs must be identified. A good way to identify indivi-
duals is by ear notching at farrowing. See PIH-114 for ear notch-
ing  numbering systems. Consider using ear tags in place of or in
addition to notches for gilts and sows.


Figure 2. Sow record.

Sow number                                 ______________________
Sire number                                ______________________
Breeding date                              ______________________
Farrowing date                             ______________________
Litter number                              ______________________
Litter birth weight                        ______________________
Number farrowed                            ______________________
   Live                                    ______________________
   Dead                                    ______________________
Number transferred                         ______________________
Weaning date                               ______________________
Number weaned                              ______________________
Weaning weight                             ______________________
Farrowing problems                         ______________________
Other                                      ______________________

     Records should be kept on each  sow  and  litter.  Figure  2
shows  an  example  of  a  sow  record card. Data from individual
record cards can be recorded in a permanent  record  book  and  a
summary  prepared  as a partial data base for future selection of
breeding stock.

     Additional records are desirable in  many  circumstances  to
utilize  boar  power more efficiently and identify breeding prob-
lems early. Keep records of the frequency of boar  services  and,
if  artificial  insemination is used, the date and volume of each
ejaculate collected. A record of the date and duration of heat is
essential  for predicting when females will next be in heat, cal-
culating dates for return to heat if conception does  not  occur,
pregnancy checking dates, and the day to bring them into the far-
rowing house. Computer programs are available for use in keeping,
organizing and analyzing records.


     Commercial gilts should be selected from largest, healthiest
litters  (based on farrowing and weaning data) as replacements on
the basis of their ability to come into heat at an early age  and
conceive  within  3  heat periods after their first exposure to a
boar. Sows should be retained on the basis of  their  ability  to
conceive  within  7  days after weaning or the earliest time that
fits your management schedule. Use of a sow productivity index as
developed  by the National Swine Improvement Federation is recom-
mended as an added selection tool.

     No matter how sperm are placed in the female's  reproductive
tract,  they must be there a few hours before ovulation to maxim-
ize the chance of getting the  best  pregnancy  rate  and  litter

     During gestation, gilts should be  fed  so  they  will  gain
about  75  lb. and sows should gain about 50 lb. Lactation should
last 20-28 days to help insure that baby pigs get  a  good  start
and  to  insure  a high rate of embryo implantation in the sow at
the first postweaning heat. At farrowing, additional pigs will be
saved  if  an  attendant  can  be  present. This also affords the
opportunity to correct problems if they occur.  Adequate  records
of  individual  performance during all phases of the reproductive
cycle will be of benefit in upgrading the herd and making it more

Related Publications

     The following PIH fact sheets contain additional information
related to swine production.
PIH-1    Management of the Boar
PIH-27   Guidelines for Choosing Replacement Females
PIH-59   Infectious Swine Reproductive Diseases
PIH-64   Artificial Insemination in Swine
PIH-68   Guidelines for the Development of a Swine Herd
         Health Calendar
PIH-74   Management of Developing Gilts and Boars for
         Efficient Reproduction
PIH-87   Cooling Swine


     Reference to products in this publication is not intended to
be  an  endorsement to the exclusion of others which may be simi-
lar. Persons using such products assume responsibility for  their
use  in  accordance with current label directions of the manufac-

% Figure 1. Effect of time of insemination on conception rate  in

Not Included: % Figure 1. Effect of time of insemination on  con-
ception rate in swine.

REV 12/89 (5M)


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.