The weaned pig output of a sow farm is dependent upon getting sufficient number
of females bred, having high enough farrowing rates so that the target farrowings/week
are achieved, and optimizing born-alive litter size and preweaning mortality.
The gilt pool is the fuel for the breeding farm. Without sufficient gilts, service
targets cannot be made and weaned pig volume and the number of farrowings that
occur fall correspondingly. The gilt pool also has significant effects on the
efficiency of breeding herd performance.
There are more gilts being bred and farrowed than any other parity. Thus, when
gilt litter sizes and farrowing rates are high, herd performance typically is
competitive. This paper focuses on how to use records to optimize farm throughput
(i.e. number of weaned pigs/unit time) in a multi-farm system as well as to
improve the efficiency by which the breeding herd produces weaned pigs (i.e.
pigs weaned/sow/year). Because the breeding herd is typically a cost center
for the finishing herd, the paper also discusses the factors that, in addition
to weaned pig volume, affect the cost of producing a weaned pig.
1. Objectives of the Breeding Herd
1.1 Production of Weaned Pigs
Efficiency of Production. Breeding
herd reproductive efficiency is most commonly measured in terms of the number
of pigs weaned/sow/year (PSY). There are two ways of expressing PSY. Pigs
weaned/inventoried female/yr (PWIFY) includes all females that have been inventoried
in the records of the herd, including gilts and sows. Pigs weaned/mated female/yr
(PWMFY) includes gilts after they have been mated as well as sows. Because
the denominator is larger, PWIFY is usually less than PWMFY and is always
less than or equal to PWMFY. As the interval from entry to service increases
or the replacement rate of a herd rises, the ariance between PWIFY and PWMFY
increases. Similarly, the difference between the two measures of PSY increases
as the interval from entry to removal of gilts and the preservice removal
rate increases.
PSY is driven by two factors: the number of litters/sow/year (LSY) and the
number of pigs weaned/litter (PWL). Similar to PSY, LSY can be expressed either
in terms of the total number of females inventoried in the herd or the number
of mated females. LSY in comprised of the number of nonproductive days/sow/year
(NPD), lactation length (LL), and gestation length (GL), according to the
following formula:
LSY = (365-NPD)/(GL + LL)
The parameter NPD is typically
expressed on an inventoried female basis. It is comprised of 8 subcomponents:
entry-to-service, entry-to-removal (by culling or death), weaning-to-service,
weaning-to-removal, service-to-detected open (by ultrasound, recycle, visual
detection, failure to farrow), service to removal, detected-open-to-reservice,
and detected-open-to-removal NPD. Nonproductive days reflect intervals and
counts of females passing through those intervals. For example, entry-to-service
NPD are a measure of the entry-to-service interval, as expressed in days,
and the number of gilts entering the herd during a period of time, as reflected
in replacement rate.
PWL can be expressed in terms of the number of pigs weaned/sow farrowed (PWSF),
the number weaned/sow weaned (PWSW) and the number weaned/litter weaned (PWLW).
Because of the denominator effect, PWSF is typically less than either PWSW
or PWLW.
Similarly, PWSW is usually less than PWLW. PWL reflects the number of pigs
born alive/litter (PBA) and the number of preweaning deaths/litter (PWD).
Born-alive litter size reflects the total number of pigs born alive (TPB)
corrected for the number of pigs dying during the birth process, called stillbirths
(SB), and the number dying prior to the onset of farrowing, called mummified
pigs (MUM).
1.1.2 Throughput. The output
of a breeding herd is most commonly measured in terms of the number of
pigs weaned per unit time, typically pigs weaned/week. Weaned-pig output
can be manifest as an absolute number or as a percentage of a budgeted
value.
Along with weaned-pig cost, weaned-pig output is one of the most common
endpoints of breeding herd throughput. Weaned-pig output is driven by
weaned-litter size (i.e. number of pigs weaned/litter weaned) and the
number of litters weaned per unit time. In turn, litters weaned/week is
driven largely by number of females served/week.
The number of females served into a breeding group is dependent upon the
size of four subpopulations in the herd: (1) weaned sows, (2) opportunity
sows, (3) females that return to estrus following mating (recycles), and
(4) gilts in the available pool. The opportunity sow pool is comprised
of sows that have not returned to heat within seven days, called late
weaners (LW), sows that have been weaned prior to 14 days of lactation,
called early weaners (EW), sows that have aborted (ABORT), females that
have been found to be negative by ultrasound tests of pregnancy or visual
examination for pregnancy (PCN), and females available to be bred if needed
but otherwise destined to be culled, called active culls (AC), As shown
below, the steps that must be taken to achieve breeding targets are highly
dependent upon the gilt subpopulation. In order for service targets to
be consistently met, record systems must be established that capture pertinent
endpoints.
1st
Calculate the budgeted number of farrowings/week. Calculating the budgeted
weekly farrowings is necessary in order to achieve the desired utilization
of farrowing facilities, and to determine the farrowing group size and
“flow” of females through the farm. Budgeted farrowings should
consider the percentage of farrowing sows that are early and zero weaned.
Key factors influencing budgeted farrowings include: (1) stage of gestation
that females are loaded into farrowing, (2) desired lactation length,
and (3) number of rooms to farrow each week. Targets for number of farrowings/week
are greater than budgeted
numbers and are usually
determined by having females loaded into farrowing at a later gestation
date, having them weaned at a shorter lactation length, and by farrowing
more rooms of sows weekly.
2nd Do
a “gilt needs projections” for the farm. Gilt needs projection
computations are necessary so that sufficient gilts are available to meet
service targets throughout the year. Establishing the gilt needs for a
farm is dependent upon the budgeted replacement rate for the herd, the
seasonal change in farrowing rates, and the number of females that have
already been served into existing service groups (i.e. the size of holes
in breeding groups that must be filled). Note, because PCP and post ultrasound
fallout rates fall when females are mated during the summer, more females
have to be mated. Until the sizes of recycle and opportunity sow pools
increase in response to the seasonal drop in fertility, the sow herd inventory
must be grown by increasing the size of the gilt pool, if service targets
are to be achieved.
4th
Set service targets. Service targets must be set dynamically according
to anticipated changes in farrowing rate. Seasonal changes in fertility
are abrupt, often occurring within 2 to 4 weeks. New Fashion Pork, Inc,
(NFP) uses % budgeted services as a bonus incentive for its breeding departments.
Thus, we reset service targets monthly. Records of ultrasound diagnostic
tests can be used to predict farrowing rates based upon 28-day ultrasound
tests and the percentage of females falling out between the 28-day test
and farrowing (% fallout).
5th
Organize the breeding barn. Barn organization is essential if all subpopulations
of females are to be easily found and available as needed. Gilts should
be organized in pens or stalls by age and/or the occurrence of skip-heat
events. Females that have been skip heated must be clearly identified
as to the week that they will return to heat. The breeding barn must be
set up with an “opportunity sow area” where each type of opportunity
sow (e.g. LW, EW, PCN, ABORT, AC) is clearly identified. Recycles must
be pulled from their old group in the gestation snake as they are found
in heat and replaced in the breeding line or with their new service group
in the gestation snake. Open spaces in the gestation snake must be promptly
filled with pregnant females from the parking area as soon as animals
are detected open.
6th Develop
weekly service budgets. Service budgets are a weekly plan for how budgeted
number of services will be achieved. The plan is developed weekly late
in the week prior to when females are to be bred. It should project the
overage/underage for number of females likely to be bred based upon (1)
the number of weaners predicted to return to estrus following weaning,
(2) the number of available gilts (including skip-heat gilts) predicted
to come into heat, (3) the number of served females likely to return to
service (recycles) and (4) the number of opportunity females projected
to return to heat during the following week. Weekly service budgets must
be monitored closely (e.g. at quarterly intervals) to ensure staff compliance.
In order for them to be useful, breeding barn staff must be forced to
use service budgets. This can be accomplished by periodically checking
how close the service budgets prepared one week actually match what was
mated on the following week
7th
Monitor the breeding system. The breeding system should be monitored weekly
to ensure that budgets and targets are being achieved and that subpopulations
are being managed as planned. The monitoring of gilt-related activities
is particularly important, since this is the one subpopulation, of the
four subpopulations in the service pool, which can be most easily manipulated
in order to achieve service targets. There are several areas warranting
special attention. Are the budgeted numbers of gilts being served each
week? Are gilts being mated at the budgeted age? Are sufficient gilts
being skip heated before they are bred? As discussed below, a gilt availability
report will need to be designed to enable the viewer to efficiently and
effectively manage the gilt pool.
1.2 Weaned Pig Quality
The quality of lots of weaned pigs is typically measured in terms of average
weaning weight. As producers attempt to improve the performance of the growing
pig, their record systems are increasingly being used to track the number
of pigs that (1) are not weaned at a certain minimum weight, (2) have defects
(e.g. hernias, injuries), (3) have been castrated, (4) do not show signs of
disease, and (5) are free of diseases potentially impacting their performance
during the growing phase.
1.3 Herd Health
With the co-emergence of high health breeding herds and the pathogen Porcine
Reproductive and Respiratory Disease Virus (PRRSV), disease became “king.”
Herds periodically become unstable, from a health standpoint, resulting in
fluctuations in weaned pig output and quality. Level of immunity to most diseases
varies over time in a herd. The presence of subpopulations of females in the
herd that are in different phases of the reproductive cycle contributes to
temporal variations in herd immunity.
The gilt is the most important
cause of herd health instability. Shedding gilts carry pathogens into the
herd with them thereby exposing naïve individuals in the herd. Naïve
gilts can be exposed post entry to shedding sows in an unstable herd. Either
way, infusing gilt into a herd is similar to “pouring gasoline onto a
fire.”
In an effort to better understand and control diseases, producers have begun
developing databases that capture routine serology and post mortem information.
For example, NFP monitors its sow herds quarterly, taking samples from females
that have been bred 1, 4, 7, 11 and 15 weeks and sows that have been lactating
for 1 week. In a similar cross-sectional sampling frame, groups of unbred
gilts are subsampled every 3 weeks from the time they enter the gilt development
unit (GDU) through the time that they are mated.
2. Measures of Performance
2.1 Budgets and Targets
Budgeted numbers refer to what you project that a farm will do. Because they
are readily achievable, they are usually the numbers that are used in forecasts
for lenders and owners. Budgeted numbers are also the numbers used to compute
input use rates.
Targeted numbers are what a farm strives to achieve. They should be “a
reach;” that is, not readily achievable, but achievable with reasonable
extra effort. Both budget and target numbers should be calculated for endpoints
used to measure how well gilts are being managed.
2.2 Gilt Pool Management Endpoints
There are several endpoints used to assess how well farm staff members are
managing a herd; several relate to how gilts are managed and others pertain
to the entire population of females. Relative to gilts, some endpoints assess
how well either chronological or physiological age is being managed. Some
assess how well farm staff members are managing the inventory of gilts in
the farm or its gilt development unit. Other endpoints can be used to assess
how quickly gilts are bred or made available to be bred.
2.2.1 Age-related Endpoints.
Several endpoints can be used to assess how well the system is being executed
to optimize the maturity of the gilt when first mated. These include:
- age at first service
- % gilts served greater than the budgeted minimum age
- % gilts served that have a skip heat event
- age at 1 st skip heat
2.2.2 Inventory Management Endpoints.
Several endpoints can be used to assess how
well gilt inventories are being managed. These include:
- total number of gilts in the gilt pool
- % total female inventory in herd that are unbred gilts
- number of gilts in gilt pool that are available to be bred (i.e. size
of available gilt pool)
- ratio of number of available gilts to number needing to be bred. If
all available gilts are cyclic this ratio would be 3:1. Typically, when
available gilts are a blend of cyclic and acyclic gilts, this ratio
will be greater than 4.5.
- % replacement rate
- % gilts entering a herd that are removed prior to service
- % selection rate (the proportion of gilts entering a gilt development
system that eventually make it into the breeding herd)
2.2.3 Intervals Relating to Gilt
Management. The key endpoint used to assess how quickly the gilt
becomes productive is entry to 1st service interval. It can be
decomposed into its two components:
- entry-to-available interval
- available-to-1st -service interval (days from becoming
available until served)
2.3 Productivity Endpoints
2.3.1 Prime Numbers of Productivity.
Prime numbers are those that cannot be readily decomposed into
component parts. They are the key drivers of herd productivity. Prime
numbers of productivity that are commonly assessed include born-alive
litter size, preweaning mortality and farrowing rates. While being a prime
number for the breeding herd, at large, preweaning mortality is seldom
a problem for first-litter sows and, thus, is not a prime number used
to assess gilt performance in isolation from the remainder of the herd.
2.3.2 Sow Longevity. The
number of litters a sow has before she exits the herd, either by dying
or culling, has a major influence on the genetic cost for producing the
weaned pig.
Through its effect on the herd’s parity distribution, it also affects
the efficiency of production (e.g. pigs weaned/litter, farrrowing rate,
born-alive litter size. There are at least four endpoints that can be
used to monitor sow longevity:
- Pigs born alive/sow lifetime
- pigs weaned/sow lifetime
- litters farrowed/sow lifetime
- parity at removal
3. Establishing the Correct Gilt Flow
for a Farm
Gilt flow into the farm is the primary determinant of the number of females
available to meet service targets. Computer models are very useful in figuring
out gilt flow for a farm and size of gilt development facilities needed. Being
relatively easy to construct using
spreadsheets, they should consider the desired delivery frequency in the computation
of the number of gilts needed in each delivery. To do this meaningfully, gilt
flow models should also consider:
- budgeted age at which gilts are delivered into the gilt development system
- budgeted age at which gilts will exit the gilt development system
- budgeted age at which gilts enter the breeding farm
- budgeted age at first service
- time post mating that gilts will be put in gestation snake
- expected removal rates prior to service (after gilts have entered the herd)
- expected selection rates during development
- changes in replacement (infusion) rates during the year
- facility sizes (including the sizes of (1) the gilt development unit, (2)
housing after entry into the breeding herd but prior to being made available,
(3) housing after being made available, and (4) housing from when gilts are
bred until they are placed in the gestation snake
- budgeted floor space allowance by age of gilts
4. Informatics
There are several essential elements to the effective monitoring of performance.
4.1 Data Capture
The breeding herd is comprised of subpopulations. Females in the herd are
either bred females presumed to be pregnant, open females thought to be non-pregnant,
and lactating sows. There are four major open female types in the breeding
herd: weaner, recycle, opportunity and unmated gilt. The opportunity female
category is comprised of late weaners (not in heat by seven days after weaning),
early weaners (weaned less than 14 days of lactation), pregnancy check negatives,
and abortions.
Information on fertility and litter size should not only be captured by parity
but also by subpopulation. In addition, several bits of information must be
captured on individual gilts, including: dates of birth, entry, skip heats,
service, treatments with PG600, and
removal.
4.2 Projection of Gilt Needs
Projections must be done for a period as far in advance as possible. It is
desirable that projections be done for a time period beginning when gilts
are dedicated to a sow farm until they are available to be bred into a service
group. Accurate group sizes are typically available for (1) gestating (16
weeks), (2) lactating (3 weeks), and (3) weaned groups (1 week). Thus, gilt
needs projections can only be done accurately for 20 weeks in advance.
4.3 Monitoring of Gilt Availability
In order to improve the efficiencies associated with gilt performance, management
must ensure that sufficient gilts are available at the desired age and after
having the targeted number of skip-heat events. In well-managed systems, just
having enough gilts to achieve service targets is not enough. The gilts must
be old enough, from both a chronological and physiological standpoint.
4.4 Monitoring of Gilt Handling
How gilts are being handled by farm personnel should also be considered, including
such things as the proportions of gilts being (1) bred too young, (2) culled
prior to breeding, and (3) treated with PG600.
4.5 Monitoring of Gilt Performance
All competitive computerized information systems report litter size and fertility
by parity.
This allows the gilt’s biological performance relative to other parities
to be easily assessed. NFP uses a template, called “Ultrasound Diagnostic
Record” to determine how the gilt differs from other parities in various
measures of fertility, including pregnancy check positive rates at 4 and 7
weeks of gestation, rates of pregnancy when visually examined at 11 weeks
of gestation, and farrowing rates.
5. In-the-barn Information Systems
Real-time information management is only possible when the in-the-barn systems
tell the farm staff (1) when an event has occurred or a date has arrived keying
an action by a technician and (2) what management practice must be performed
on the gilt at that time.
While a computerized information system is a necessary tool for managing the
breeding herd, it must be supplemented by in-the-barn information systems. The
design of these systems is critical to their usefulness.
5.1 Gilt Identification
A simple method for permanently identifying gilts according to their birth
or entry date is helpful for managing gilts in the barn. NFP uses a 6-digit
slap tattoo number in which the year and week of a gilt’s birth or entry
date is included in her identification number. For example, “033124”
would mean that gilt #124 entered the herd on the 33 rd week of Year 2000.
By having entry or birth date information in the gilt’s permanent identity,
the technician has access to information that allows them to more effectively
manage individual animals.
5.2 Stall and Crate Cards
NFP uses a different breeding stall cards for each of the four major female
types (weaner, recycle, opportunity, and gilt). The stall cards allows females
to be managed real-time (i.e. in the barn), such that anyone looking at a
the card (1) has immediate access to pertinent lifetime information (e.g.
entry dates, skip heat dates, PG600 treatments) and (2) knows when certain
actions need to be taken (e.g. dates when PG600 treatments should be given,
when females should be placed in “stress pens,” when females should
be removed from the herd for failure to farrow following service. NFP also
uses different colors of cards for the different types of opportunity females
(late weaners, early weaners, females found not pregnant, aborted females,
and females identified for culling).
The farrowing crate cards used by NFP allow the user to easily understand
in chronological order the events that occurred to a sow and her litter (e.g.
foster on/off, nurse off, piglet death). While capturing farrowing and weaning
data, it also captures qualitative information on the sow and litter at birth
and at weaning. A system of colored cards is also used to identify nurse sows
and at-risk pigs and litters.
5.3 Data Capture Forms
Forms used to capture breeding information, regardless of where they are being
used in the breeding herd, should capture requisite data simply and accurately
to allow for subsequent entry into a computerized information system. Forms
should also lend themselves to being easily used by farm staff to visually
examine data as they attempt to manage subpopulations of females.
5.4 Group Numbering
Sows are identified according to the week of the year in which they are served
(i.e. 1-52).
As with sow service groups, NFP identifies each group of entering gilts with
a number consistent with either the week or 1000-day date that the gilt group
enters the herd. For example, Group 41 refers to the group that entered on
Week 41 of the year. Group 357 refers to the group that entered on Day 357
of the 1,000-day calendar. Group numbers are used to sort gilt information
so that individual group performance can be tracked.
6. Projection of Gilt Needs
6.1 Application
NFP uses a customized spreadsheet application, called the “Gilt Needs
Projections ” to determine dynamically how to vary rates of gilt introduction
into a herd. Projections are run monthly.
6.2 Basis for Projections
Steady state needs for replacement gilts are dependent upon:
- budgeted replacement rate
- herd’s breeding female inventory
- post entry selection rates
- proportion of gilts not cycling following entry
- Age when gilts enter the farm
6.3 Factors Influencing Gilt Needs
Several factors cause fluctuations in gilt needs:
- seasonal changes in fertility, percent of entering gilts served, age of
puberty, and synchrony of puberty
- group-to-group variations in weaning group size
- changes in the budgeted age when gilts become available
- changes in replacement rates (as occurs with the implementation of a parity
correction plan)
- non-seasonal temporal variations in fertility
6.4 Gilt Needs during a New Herd Start-up
The ramping up a start-up herd or the repopulation of a new herd requires
the consideration of several additional variables. In planning the infusion
of gilts into a new herd, NFP uses a custom template, called “Gilt Needs
Projections for a New Herd.” In
addition to the above inputs, it considers:
- timing and sizing of gilt deliveries to ensure that service targets are
met
- staging of gilt deliveries to ensure that gilts are mated after being
skipped heat and above a minimum age
- establishing ongoing regular replacement rates after startup is complete
7. Monitoring Gilt Pool Management
NFP captures its gilt information in a commercial software program, called PigCHAMP.
It then exports that data to a custom designed database system called the “Gilt
Availability Report.” This report allows the monitoring of how gilts are
performing after they have been delivered into the herd. It measures endpoints
weekly over time following the periodic introduction of gilt groups.
- % gilts served at greater and less than targeted minimum age
- % gilts treated with PG600
- % gilts served and % remaining to be served
- % gilts with skip heat event and age of 1 st skip heat
- % gilts culled or dying
It also allows the user to make decisions “on the fly” as to how
the gilt pool should be managed in order to achieve service targets. That is,
what you can change in gilt pool management to make sure that you achieve service
targets while maximizing gilt maturity.
8. Cost Management
8.1 Key Factors Influencing Weaned
Pig Costs
Several factors influence the cost of the weaned pig. Since most costs of
production for the breeding herd behave as fixed costs, volume of pigs weaned
is the most important determinant. In general, as the number of pigs weaned
increases, the cost of production decreases. Farm staff influence several
costs, commonly called controllable expenses.
Key controllable expenses for the breeding herd included:
- sow feed cost, primarily through the amount of gestation feed provided
each sow
- semen cost, through the number of matings/service, the farrowing rates,
and weaned litter size average
- gilt genetic cost component, through breeding herd replacement rates,
sow lifetime productivity (pigs marketed/sow/lifetime)
- labor cost, through staffing levels of farms, annual replacement rates
of staff, wages (including salary, fringe, bonuses, and other incentives)
- utilities, through the use of propane/natural gas to heat farrowing rooms
- health product cost, through compliance with vaccination schedules and
use of drugs.