HERD MANAGEMENT PIH-8
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Managing Sows and Gilts for Efficient Reproduction
Authors:
John R. Diehl, Clemson University
James R. Danion, Auburn, University
Leif H. Thompson, University of Illinois
Reviewers:
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.
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Table 1. Normal age range of puberty, estrus and ovulation.
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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)
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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
stress.
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Table 2. Suggested coefficients to determine the number of
females to be bred each month.
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Month Coefficient
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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
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Numbers to breed each month = (number of farrowing stalls) x
(coefficient).
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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-
mance.
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
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.
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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 ______________________
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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.
Summary
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
size.
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
profitable.
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
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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-
turer.
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% Figure 1. Effect of time of insemination on conception rate in
swine.
Not Included: % Figure 1. Effect of time of insemination on con-
ception rate in swine.
REV 12/89 (5M)
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