Monte
B. McCaw
For this investment in
effort and resources we expect the gilt to be productive, that is to have piglets, successfully raise them,
rebreed and become pregnant again, thus remaining in the herd, all without
initiating any production losses from clinical disease. She must be fertile, come into heat at a predictable time (earlier rather than
later), and enable elective replacement of an older sow. She should farrow a maximal number of
piglets, lactate her piglets, and likely some from an older sow with too many
liveborn and too few functioning teats.
The gilt should be robust, have sufficient body weight and capacity to
eat enough feed to not loose excessive weight during lactation to enable her to
recycle and rebreed quickly and thus remain in the herd. Finally, she should be healthy, not carrying
in any new diseases nor susceptible to any diseases that are already in
your herd.
Optimizing gilt fertility requires coordination of feeding
management, housing, properly timed boar exposure and mating. Gilts apparently do not require a special
ration during the pre-selection / finishing stage. If gilts are full-fed standard finishing rations during their
growth it appears that there is no long-term detrimental effects upon her fertility
or longevity. Once gilts are selected
(approximately 210 pounds) they should be placed upon a lactation ration. Lactation ration provides the gilt the
necessary elevated levels of protein, lysine, calcium, phosphorus, and
micronutrients. This will minimize any
risk of insufficient bone mineralization and fractures during later matings or
pregnancies. The level of feeding
leading up to mating also can impact the gilt’s performance. Flushing (increasing the gilt’s feed
allowance by 50 to 100% for 10 to 14 days prebreeding) has been shown to
increase ovulation rate and subsequently increase the number of piglets born as
much as 1.0 pig per litter when gilts were being limit fed during
development. This effect may be herd
specific, but often most pronounced in herds with low average gilt total
born. Flushing, to be effective, must
be followed by limit feeding immediately after mating (full feeding following
mating may increase embryo mortality).
Modern fast-growing gilts should be fed to maximize their body weight by
mating to maximize their chances of remaining in the herd after their first
litter. Feeding modern gilts at or
near ad libitum after final selection through puberty up until the time of
mating will maintain them in the positive energy status (“flushed”) necessary
to maximize the number of ova shed during estrus. Gilts may have reduced litter size if they are bred on their
first heat after transportation and entry into the herd because they were in a
negative energy state resulting from reduced daily feed intake during transportation
and adjustment to the new herd. Also,
pen feeding of new gilts may cause the least dominant animals to not get full
access to feed and therefore have small litter size or not cycle as early. Full feeding gilts up to the time of mating
ensures their rapid growth, sufficient size, young age at first estrus, and
maximal number of ova shed. Finally,
the age at which gilts first start to cycle is dependent upon their breed.
Crossbred animals may start to cycle 20 days earlier than purebreds. Certain breeds like the Landrace and Large
White begin cycling younger than Yorkshire or Duroc gilts.
Housing
Housing of gilts also has a major impact upon their
age at puberty, fertility, and fecundity.
It is well known that transporting gilts from one facility to another
will stimulate most mature gilts to cycle within days of arrival. However, how the gilts were raised before
that transport will affect how many will be ready to cycle and breed
successfully after arrival. A greater
percent of gilts reared in outdoor lots will attain puberty and at an earlier
average than confinement reared gilts.
Outdoor rearing of gilts is not practiced widely today, mainly for
biosecurity reasons. None-the-less we
must keep in mind the negative impact confinement rearing has upon their sexual
development. Seasonal effects on gilt
maturation are more marked in outdoor reared vs confined gilts. However, even the negative effects of
seasonal on puberty still do not negate the positive effects outdoor rearing
has upon early maturation of gilts.
Gilts apparently should be reared in groups rather than individually to
optimize their reproductive development.
When gilts were crated individually or penned in groups of 3 they reach
puberty at a much older age and at a lower rate than gilts housed in groups of
10 to 27. Gilts housed individually in
crates were also observed to have nearly double the incidence (28%) of silent
heats and irregular cycles as pen reared gilts. Also, teathered gilts have been found to have a significantly
greater incidence of immature reproductive tracts at 10 to 12 months of age
(13/87 vs. 0 / 87) versus pen reared controls.
Conversely, gilts raised in groups of 50 or more also had a lower
conception rate than smaller groups.
Therefore, it appears gilts are best reared in groups of approximately
10 to 30 animals. Density of gilts in
the developer pens appears to have no effect on the age of puberty. However, PIC recommends 12 square feet per
gilt space, possibly to minimize the risk of injury from fighting among
animals. Gilts can be raised with
barrows with no bad effect on their sexual development. However, gilts should not be exposed to
mature boars until they are approaching puberty (see below). The gilts’ environment can also affect her development
and fertility. Dr. Flowers found
environmental temperatures of 90oF reduced the proportion of gilts
reaching puberty by 230 days from 90% to > 30%. Approximately half of the gilts reared at the higher temperatures
had cystic ovaries. Also, excessive
environmental temperature increases embryo mortality if the gilt is exposed
between mating and day 16 gestation, thus decreasing the number of piglets born
live. Conversely, gilts housed
individually in wet conditions or with a lot of draft will experience greatly
reduced effective environmental temperatures.
These gilts will need more feed to maintain their expected rate of
growth and body condition and thus a positive energy status for optimal
fecundity at mating. Finally,
environmental gases may also play a role in the gilt’s reproductive development
as 20ppm ammonia was found to delay puberty by 7 to 10 days in 15% of gilts
tested.
Boar
exposure is essential to stimulating gilts to mature earlier and express visible
estrus. Properly timed boar exposure
can stimulate gilts to cycle as much as 40 days earlier than non-stimulated
controls. This is critical to minimize
feed and housing costs of gilt development.
Also, early puberty enables producers to wait and breed gilts on their
second or third heat. One pig or more
liveborn per litter can be gained by waiting to mate gilts until their second
or even third estrus. Given that gilts
generally farrow 25% of the herd’s litters, this may be a very significant gain
for herds with low liveborn problems.
To achieve early puberty and optimal gilt
reproductive performance four things must be accomplished: 1) do not start boar exposure at too young an age (<160 days),
this makes gilts much less responsive to his effect when they approach puberty 2) use mature (>10 months old) boars
for gilt exposure 3) take gilts
daily to a strange pen to be exposed to the boar (either the boar pen or a
breeding pen) 4) direct physical contact with the boar by the gilt is critical, fence line contact not good enough. Only 5 to 15 minutes of boar exposure is
needed per day to get the desired effect.
The rest of the time, house gilts away from boar contact and scent.
Once the gilts approach puberty their estrus cycles
can be synchronized by transporting them to a new facility. If the final stages of gilt development are
performed “on farm” or if boar exposure in the gilt developer is not possible
then maximizing the number of sexually mature gilts AND synchronization of gilt
estrus may be difficult to achieve simultaneously. Rotating boars used to expose gilts with may improve the
proportion of gilts that will begin cycling and therefore mate. Realize, that there appears to be an
association between how quick gilts come into heat following boar stimulation
and their subsequent lifetime fertility.
Usually gilts quick to show estrus are more fertile (return to heat
quickly, high conception rates) than slower to cycle animals. If gilts are to be naturally mated, mate
them immediately upon observing standing heat.
Vasectomized boars can be used to stimulate heat in young gilts and
still prevent unwanted / recorded matings.
Allowing the vasectomized boar to mount and “breed” the gilts on their
first estrus may have positive effects upon subsequent litter size. However, be certain to wait 6 weeks after
surgery to ensure no viable sperm is in his ejaculate. Also make sure the vasectomized boar is
mature (old) enough to stimulate the gilts with his odor and mating
activity. Finally, abortion of bred gilts
early in pregnancy (< 42 days of pregnancy) and rebreeding them upon their
first estrus (96 hours later) can be a very reliable method of timing their
entry into specific breeding groups.
We expect gilts and sows to lactate or feed their piglets. That we can’t do it easily or economically is evident by the reduction in swine units attempting to use the Segregated Early (7 to 14 days) Weaning management system. However, how frequently do we cull based upon the number of pigs weaned? At what level of priority is lactation ability ranked among factors used to decide whether a sow is kept in the herd or not? Certainly it’s ranked below ability to walk and become pregnant, and farrow a few liveborn piglets. But how much lower should it be ranked, if at all?
Lactation
is half of the sow’s purpose in the herd.
Sows must be able to feed the piglets that are born
alive; otherwise the piglets die. Piglets commit to and suckle from only one
teat. Therefore, the number of functional teats controls the number of piglets
that are weaned. Functional teat number
is vastly overlooked! Functional teat
number is the most limiting factor to the number of pigs weaned per sow or per
week in most of out herds.
Today, with our aggressive breeding programs and
sows selected for large litter size / liveborn, it is rare to find herds where
the number of pigs born alive doesn’t exceed the number of functional teats
available to feed them. Also, with many
states implementing waste management control plans that also limit the number
of sows per site, we are now unable to “over farrow” each week to meet our
production goals in less efficient herds.
Therefore, to maximize our sow herd’s productive efficiency we must
include the number of pigs each sow weans in our culling decisions and select
gilts with a large number of well spaced and formed teats in their
underlines. The following calculations
illustrate the impact of number of functional teats available (number of pigs
that can be weaned) upon preweaning mortality and obviously the number of pigs
weaned per litter.
10 litters
Ave
Weaned 9.2 92 weaned
13
died =
12.4% PreWeaning Mortality
Ave
LB 11.0 110 born
Ave
Weaned 9.2 92 weaned
18
died = 16.4% PreWeaning Mortality
After
increasing number of functional teats in the group by 5 to handle the increased
number of pigs born alive.
Ave
LB 11.0 110 born
Ave
Weaned 9.7 97 weaned
13 died
= 11.8% PreWeaning Mortality
How can we change the
average number of functional teats per sow (per crate)?
By increasing the average number of functional teats
per sow we will increase the average number of pigs weaned per crate, therefore
per room and ultimately per week by the herd!
Simply put, the average number
of functional teats per sow can be increased by: 1)
carefully selecting gilts with a large number of evenly spaced well formed
teats and 2) culling sows with poor underlines (damaged teats, rear
udders that swing freely, mastitis, or are too big for piglets to reach the
teats easily) and / or wean low numbers of pigs. Obviously we need to have 1) enough gilts to replace these
voluntarily culled sows and 2) be certain that the gilts will definitely
wean more pigs than the sow she replaces.
I feel that, barring obvious disease of the litter or sow, that low
number of pigs weaned by middle to older aged sows will very likely be repeated
in the next litter. What we may lose in
number of pigs born alive by replacing that sow with a gilt I believe will be
made up for by the increased number of pigs weaned by the gilt. Remember, we currently are farrowing more
pigs than most of our sows can wean, therefore fostering (at birth) some of the
extras onto gilts will help increase the number of pigs weaned and decrease
preweaning mortality at the same time!
In short we must maximize the number of functional teats in each room to
maximize the farrowing herd’s weaning performance. Therefore, it is critical that we manage the gilt pool so we have
enough gilts available to replace older poor milking (as well as non-breeding
or lame) sows that need to be replaced.
This allows for voluntary sow culling rather than the involuntary and
therefore reactionary or emergency type replacement programs we’re often forced
to use when gilt supplies are tight.
We need to ensure gilts enter the breeding herd in robust body condition. We must maintain that condition through gestation and especially their first lactation to maximize the chances of their rebreeding successfully and remaining in the herd long-term. Therefore active attention must be focused on both pre-pubertal as well as lactation gilt feeding practices and rations. If the gilt is not robust upon entry into the breeding herd, and not maintained in that condition, she is very likely to fail to cycle or conceive and be culled by second parity. This is particularly true of gilts that produce a lot of milk / feed a large first litter. Particular attention must be focused upon the amino acid levels as well as energy and calcium / phosphorus levels of the gilt rations. Gilt growth targets should be an 100 pound gain from breeding to farrowing, sows 75 pounds. Particular care needs to be made in ensuring all gilts in pen gestation situations get their needed amounts of feed for growth and condition maintanance. The least dominant animals are at a high risk of not gaining the necessary amount of weight during their first pregnancy and therefore are likely candidates for culling after weaning only one litter. In lactation for every 1% loss in weight (as fat) by parity 1 sows there was a decrease of 0.12 pigs born, 0.14 pigs weaned, and 2.2 pounds less litter weaning weight in the second parity. Sows should gain 25 to 35 pounds between farrowings. For some of our hybrid sows we need to also pay attention to their size and body condition for entering lactation. If they are too fat, they may not eat as much in lactation, lose a higher percentage of body weight, enter a negative energy state, and ultimately not rebreed. To minimize gilt weight loss and maximize their lactation feed intake we may need to consider feeding them three to four times a day after first week of lactation. It appears that nitrogen (protein) loss during pregnancy may actually be more important than energy / fat losses to subsequent reproductive performance and retention in the herd. This appears to be particularly true during the first lactation. We may need to consider a gilt weighing and ultrasonic probing to measure back fat and loin eye size before and after lactation to access the effectiveness of our feeding management.
Finally, we expect gilts to be Healthy additions to
the herd. Health in this setting means
that the gilts neither
bring in new disease nor are susceptible to diseases already present in the
herd. In the second situation, commonly
seen in PRRSV infected herds, as the proportion of non-immune animals in the
breeding herd increases, so to does the risk of clinical disease
reoccurring in the herd. To prevent
introduction of unwanted new diseases we must test animals both before delivery
and while in isolation to ensure they are not infected before being added into
the herd. Closely observe new gilts and
boars daily in isolation for any
abnormal signs including cough, diarrhea, lack of appetite, depression, reluctance
to move, rough hair coat, bad colored feces, pale color, rapid breathing,
etc. The cull animals from your herd
can be used as both clinical signs sentinels an should be tested at the same
time for sero-conversion to unwanted diseases following exposure to the new
gilts. Also, blunt discussions by your
veterinarian with the selling producer and their veterinarian (should include
diagnostic test charts of regular repeated testing in the source herd) should
be had before sale as to whether the disease has been observed. Also ask what are the measures taken to
identify whether the infection may be in the herd and what is done to keep it
out. Gilts must be made immune to diseases
already present in your herd. This can
be accomplished by vaccination with commercial vaccines, exposure to clinically
affected animals, or feed-back of infected tissues or feces (TGE, rotavirus,
PRRSV?) while the animals are in isolation.
Each herd needs its own set of immunization procedures since they each
have different disease profiles. The
gilt feed-back or exposure procedure must be limited to use in isolation only
because the gilts may shed enough bacteria or viruses to actually overcome the
immunity of older sows in the herd causing clinical repeated disease even in these
animals. Feed-back can be accomplished
with feces from piglets in the farrowing house, infected pig intestines,
mummies, or with housing gilts with cull animals from the main herd. The best cull animals to use are un-bred
cull gilts or possibly very old and thin sows.
Successfully infecting gilts in isolation is actually very difficult to
do consistently. To improve the rate of
infection, trade pens of gilts with the cull animals daily (keep the same
animal groups, move the groups to different pens). Also, don’t wash out the isolation room between groups of gilts
to improve chances of successfully infecting them. However, if an unwanted disease is detected in gilts during
isolation, thoroughly clean and disinfect the isolation unit after selling the
infected gilts and before bringing in a new group. Success or failure of infection must be monitored by testing
gilts at entry and again prior to release into the breeding herd. We have to assume they are immune following
developing an antibody response. All
testing, exposure, and observation procedures must be repeated religiously for
each set of gilts entering the herd.
One single slip or certainly repeated systematic lazy omissions in gilt
vaccination or acclimatization (exposure to home-herd infections in isolation)
will result in exceptionally costly losses (for example PRV, TGE, PRRSV,
Influenza, disentary, etc). To maximize
the usefulness of the isolation time expose gilts to a boar, observe and record
estrus dates in isolation to aid efficient and effective gilt insertion into
the herd.
Take-Home
Messages:
·
Make sure gilts are fed for rapid growth
·
Make sure gilts get fed heavily before breeding and
for growth during gestation (maintain a 3.5 body condition score)
·
Make sure gilts are exposed to boars to stimulate
early estrus
·
Breed gilts only after their first estrus
·
Select gilts also by the number and spacing of their
teats
·
Cull sows that don’t wean many pigs
·
Maintain enough gilts in the gilt pool to allow for
voluntary (non-death non-reproductive) culling.
·
Make sure gilts and sows are fed as much as they
will eat in lactation to ensure they can come into fertile heat again and be
rebred. Feed gilts 3 – 4 times per day
in the second and third weeks of lactation.
·
ISOLATE AND TEST ALL HERD ADDITIONS! REJECT groups found to be infected with
unwanted diseases.
·
Determine which diseases you have and which ones you
don’t have in your herd. Design (with
your veterinarian) and follow religiously a vaccination, exposure, or feedback
program in isolation. Test new gilts
negative for new diseases before allowing them to enter the sow herd. Test gilts to cross-check that they have
been successfully exposed (acclimatized) to the diseases in your herd that they
were not immune to upon arrival.
