Maximizing throughput or production of a pork enterprise begins with the breeding herd. In order to achieve a consistent flow of pigs, and the minimum variation biologically possible, sows must first be bred, piglets born, and viable pigs weaned in sufficient numbers to meet production targets.

For most producers, between 18 and 26 pigs are produced annually, for every breeding female. The sow herd eats and takes up space and labor regardless of productivity, so it costs almost as much to produce 18 pigs as 26.

Obviously, there is a great deal of variation in pigs/sow/year (P/S/Y) between farms. The P/S/Y that can be achieved by an operation is dependent on facility type, management practices, health, nutrition and genetics.

Also, fluctuations in pig flow occur from changes in management practices, health and personnel throughout the year. Many farms also experience seasonal effects on reproduction.

With all of these factors and the inherent biological variation, pork producers face a stiff challenge to optimize reproductive efficiency and maximize throughput.

Establish Your Goals

What is optimal reproductive efficiency for the breeding herd? As previously discussed, P/S/Y is a good measure, and the most commonly tracked statistic for monitoring performance of the breeding herd.

However, to truly measure the impact of reproductive efficiency on throughput for the entire operation, a more complete statistic would be the pounds of weaned pigs/mated female/ year (Figure 1, page 14).

With this measure, not only are the numbers of pigs produced by each female tracked, but also the size and viability of the weaned pigs, which will impact their future performance and variability in growth.

A reasonable goal would be 275 lb. of weaned pigs/mated female/year. This can be achieved with 2.3 litters/mated female/year, 11 pigs born alive/litter, 9% preweaning mortality and weaning 12-lb. pigs at an average age of 18.5 days. These components then become our areas of opportunity for improvement.

Achieving Your Goals

To maintain optimal reproduction and throughput, a complete understanding of an operation and its productivity are required. Table 1 provides some key productivity indicators to maximize throughput, along with suggested target values. Which indicators to focus on will depend on individual operations.

Most farms should verify that they have targeted an optimal weaning age, work toward increasing the average parity of the sow herd and achieve two matings per service period. Herds with a low P/S/Y should focus on improving breeding techniques that enhance farrowing rate and reduce non-productive sow days. Farms that are average in P/S/Y should look at methods of improving litter size in addition to breeding techniques. Farms that are already doing an excellent job with P/S/Y can look more closely at reducing preweaning mortality and improving litter weights to further maximize throughput.

The need for farms to focus on differing areas based on productivity is illustrated in Table 2. Good breeding techniques and low non-productive sow days make it possible to achieve 2.5 litters/sow/year. When comparing the three sections of Table 2 (blue, black, red) on page 16, it becomes apparent that litters/sow/year and the traits and management techniques that impact it are the most important factors in maximizing P/S/Y.

Obviously, improvements in the number of live born pigs will also increase P/S/Y — but even with 12 live piglets, if litters/sow/year is 2.1 or less, 25 P/S/Y cannot be achieved. Table 2 also demonstrates how reducing preweaning mortality can improve throughput, but large reductions in mortality often come at a fairly high cost.

The remainder of this article will describe in greater detail these indicators and their impacts on optimal reproduction and maximum throughput.

Litters/Mated Female/Year

To maximize the annual pounds of weaned pigs/mated female, an optimal number of litters/female must be achieved. The PigChamp datashare program reports that the top 10% of participating farms achieve 2.5 litters/mated female/year, while the lower 10% reach only 2.08. This results in a 20% reduction in throughput, assuming equivalent performance in other parameters.

Non-productive days: The most significant factor that affects litters/mated female/year is non-productive sow days. The best opportunity for improving throughput and minimizing non-productive days is by reducing the interval from weaning to insemination. Even with older weaning ages, greater throughput can be achieved if the breeding female is pregnant within five days after weaning.

Areas to focus on when reducing non-productive days include sow feeding programs, body condition, insemination techniques, estrous detection, pregnancy detection, gilt pool management, weaning age, parity distribution and sow mortality and culling.

Breeding technique and conception rate: Assuming the sow herd is reproductively healthy and fertile semen is provided, conception rates are most greatly influenced by the breeding technician and his/her heat detection methods and insemination technique. It is not surprising that there are dramatic differences in breeding technicians (Table 3 on page 17).

Technicians need an adequate knowledge of physiology and anatomy in order to make prudent decisions while inseminating females. Careful training of personnel charged with breeding the females, coupled with tracking their performance and a program for continual process improvement, can increase throughput. Reproductive performance also tends to be greater for farms that achieve a higher percentage of multiple matings.

Another concern is what is referred to as insemination fatigue. Farrowing rates may decline when individuals are presented a large number of females in estrus at a given time (Table 4 on page 17). Strategies should be in place to detect and correct this potential problem. Develop a standard routine with rest breaks after 10 to 15 sows.

Research has also shown that reproductive performance of females and boars is higher on farms where animals don't fear humans.

Heat detection: Careful heat detection is essential to minimize the number of non-productive sow days and weaning-to-insemination interval. The failure to detect estrus or breed a sow when in heat will automatically add another 21 days to the number of non-productive sow days.

Heat detection is very labor-intensive and time-consuming, so consequently, most operations do not check heat more than once per day. What becomes more important is the thoroughness and quality of heat detection.

It is important to remember that each female is an individual and will show slightly different signs of estrus. Systematic and consistent heat checks enable one to become familiar with the normal situation of all females and when they are in estrus. The standing reflex is enhanced by intense periods of boar exposure.

However, prolonged boar exposure may result in habituation and fatigue. Use boars to check for estrus in small groups. If the boar is placed in the alley in front of the sow, then estrous detection is a two-person job: one handles the boar and the other checks the sow.

Weaning age: Weaning age is obviously another important influence on litters/mated female/year. But to optimize overall reproductive efficiency, weaning age must be set at an optimal level. Reducing the lactation length will decrease the subsequent fertility of the female by extending the weaning-to- insemination interval, reducing conception rate and decreasing subsequent litter size.

Therefore, to maximize throughput in an operation, the weaning age must be set where it does not significantly reduce sow reproductive performance. In most herds, the greatest impacts on reproduction are observed for lactations of less than 17 days. If a sow is to be rebred, she needs a minimum of three days of nursing to suppress the secretion of lutenizing hormone, avoiding the formation of follicular cysts, or the sow may exhibit erratic estrous patterns or remain anestrus. Carefully monitoring and maximizing lactation feed intake to achieve more than 12 lb./day can minimize the impact of shorter lactations.

Sow feeding and condition: Nutrition and feeding management play a vital role in reproductive performance during each phase of the cycle.

After selection, the gilt pool should be limit-fed to prevent over-fattening prior to breeding, which will impact reproductive performance.

For sows, the feeding period from weaning through rebreeding is critical to reverse the severe drain on nutrient reserves during lactation and to promote conception. However, some level of feed restriction is required to reduce milk flow. Generally, 6 to 8 lb. of feed is appropriate.

Nutritional management during gestation should provide planned increases of 80-100 lb. for Parity 1, 80-90 lb. for Parity 2-5, and 55 lb. for sows greater than five parities. These targets should vary according to sow maturity, body weight at breeding and body condition. Overfeeding during gestation has a well-documented detrimental impact on feed intake during lactation that results in tissue loss for the sow, decreasing her ability to return to estrus.

Maximum feed intake needs to be achieved during lactation to maintain body condition. Extremely thin sows resulting from inadequate energy intake during lactation often experience reproductive failure. A dip in litter size occurs on some farms for Parity 2 sows. The body condition of the sows at Parity 1 during farrowing, and their management during lactation, likely play major roles in whether litter size dips in Parity 2.

Feed intake during lactation is maximized by increasing feeding frequency, ensuring that feed is fresh, increasing the energy density of the diet, and providing for a constant water supply that can deliver 0.25 gal./minute.

Parity distribution: Herds with a high throughput also tend to have a higher average parity. Higher average parity will result in decreased wean-to-estrus interval, increased farrowing rate and increased litter size. Parity 1 sows often exhibit a 0.5- to 2-day longer wean-to-estrus interval than multiparous sows.

Gilts typically exhibit a 10 to 15% lower farrowing rate than multiparous sows. Farrowing rate will remain relatively constant from Parities 2 to 5, but will decrease with high-parity sows.

Generally, litter size is also lowest at Parity 1, increases up to Parity 4 or 5, then tends to level off until it begins to decrease around Parity 7 or 8. In addition, younger sows are more susceptible to increased non-productive sow days associated with reduced lactation length than higher-parity sows.

All of these factors, plus the investment in breeding animals, demonstrates the need for producers to maintain a higher average herd parity to retain more females at, or near, their peak reproductive performance.

Sow mortality and culling: The loss or removal of sows from the herd for non-reproductive reasons will also reduce the overall reproductive rate by increasing non-productive sow days and lowering the average parity. Careful selection of replacement females plus proper management can reduce both sow mortality and sow culling rates.

Gilt pool management: Management of the gilt pool will also significantly contribute to non-productive sow days. If the average gilt is bred on her second or later estrus, another 21 to 42 days will be added to non-productive days. Focus on proper feeding, health acclimation, boar stimulation, heat detection and breeding.

Live Born Pigs/Litter

The contribution of litter size to throughput is important, but not as great as minimizing non-productive sow days. While the genetic program plays an important role in litter size, remember heritability is only 10%. This means 90% of observed variation in litter size is due to other factors.

To maximize the genetic contribution of litter size, a sound genetic improvement program should be followed, along with production and selection of parent females that have maximum maternal heterosis.

To achieve large litter size, sows should be fed to appetite (6 to 8 lb.) postweaning and for the first three weeks of pregnancy. Both high- and low-feeding levels for the first three weeks may compromise the number of fetuses.

Stress prior to, during and following breeding can produce high levels of embryo mortality. Stress on the female can be in the form of physical stress from handling, interacting with other animals or heat stress.

Animals should always be properly handled and not fear their caretakers. It is also important to avoid or reduce sow movement or mixing, especially during critical periods of gestation.

One of the most common mistakes in management is a failure to recognize that females during breeding and gestation are also susceptible to heat stress when temperatures reach and exceed 80-85°F for any period. Heat stress has its most detrimental effect on reproductive performance during two critical stages of the gestation period — the first 30 days and the last 30 days.

In the normal breeding female, 30% of the potential litter number (number of eggs ovulated) are lost within the first 30 days of pregnancy, making management of the female in the first 30 days critical to the production of large litters of viable pigs.

Preweaning Mortality Rate

Mortality of newborn pigs at or soon after birth also represents a major loss of throughput. Preweaning mortality is reduced by attended farrowing, a warm and hygienic environment, adequate care and nutrition of the mother and heavier birth weights.

The easiest way to decrease preweaning mortality is to have a stockperson present during farrowing. Balance the additional labor costs against potential gains. Through attended farrowing, struggling piglets find the udder and are able to nurse and consume adequate colostrum. Also, piglets that would be crushed can be placed in a safe spot under a heat lamp until they can compete for a teat.

Providing the proper thermal environment is the second most critical aspect to reducing preweaning mortality. Ensuring that the sow is not too hot, and the piglets are warm, can be difficult. However, success in both areas will allow the sow to have maximum feed intake, providing the pigs with greater nutrition and greater ability to combat the challenges of malnutrition and disease.

A clean environment also goes a long way in providing a disease-free environment for both the sow and the piglets. Sow health cannot be overlooked. Unhealthy sows, lame sows, and sows with pressure sores are less likely to be adept at lying and responding to their piglets and thus have a higher incidence of crushing.

Target Weaning Weights

The weaning weight of the pig will play a role in the throughput experienced in the nursery and finishing phases. In general, minimize the number of pigs that are less than 9 lb. at weaning. Tracking litter weaning weights and the number of lightweight pigs in a litter can be useful in recognizing problems.

Common reasons why pigs may be below target weaning weights include weaning age, light birth weight, increased number born alive and lack of adequate nutrition from the sow, or diseases like scours, porcine reproductive and respiratory syndrome, joint infections or Streptococcus meningitis.

Table 1. Productivity Measures to Maximize Throughput
Datashare Summarya
Productivity Measure Suggested Value Mean Upper 10% Lower 10%
Pigs weaned/mated female/year > 19 19.1 23.3 17
Non-productive sow days < 60 74 47 103.5
Weaning age, days < 24 18.2 21.1 15.2
Farrowing rate, % > 80 75.6 84.8 64.1
Number born alive > 10.0 10.3 11.1 9.5
Average sow parity > 3.5 3.5 4.3 2.7
Preweaning mortality, % < 14.0 13.4 8.7 17.7
Multiple matings, % > 95 83.4 99.5 66.7
Sow mortality, % < 8.0 7.8 3.2 13.1
21-day litter weight, lb.b > 120
aData for 2003 reported from 199 U.S. farms
bNot reported in PigChamp Annual Datashare Summary
Table 2. Achieving Pigs/Sow/Year Targets with Differing Live Born Pigs, Preweaning Mortality and Litters/Sow/Year
Preweaning Mortality, %
Born Alive 4 6 8 10 12 14 16 18 20
12 28.8 28.2 27.6 27.0 26.4 25.8 25.2 24.6 24.0
11.5 27.6 27.0 26.5 25.9 25.3 24.7 24.2 23.6 23.0
11 26.4 25.9 25.3 24.8 24.2 23.7 23.1 22.6 22.0
10.5 25.2 24.7 24.2 23.6 23.1 22.6 22.1 21.5 21.0
10 24.0 23.5 23.0 22.5 22.0 21.5 21.0 20.5 20.0
9.5 22.8 22.3 21.9 21.4 20.9 20.4 20.0 19.5 19.0
9 21.6 21.2 20.7 20.3 19.8 19.4 18.9 18.5 18.0
8.5 20.4 20.0 19.6 19.1 18.7 18.3 17.9 17.4 17.0
8 19.2 18.8 18.4 18.0 17.6 17.2 16.8 16.4 16.0
Litters/sow/year = 2.5
Preweaning Mortality, %
Born Alive 4 6 8 10 12 14 16 18 20
12 26.5 25.9 25.4 24.8 24.3 23.7 23.2 22.6 22.1
11.5 25.4 24.9 24.3 23.8 23.3 22.7 22.2 21.7 21.2
11 24.3 23.8 23.3 22.8 22.3 21.8 21.3 20.7 20.2
10.5 23.2 22.7 22.2 21.7 21.3 20.8 20.3 19.8 19.3
10 22.1 21.6 21.2 20.7 20.2 19.8 19.3 18.9 18.4
9.5 21.0 20.5 20.1 19.7 19.2 18.8 18.4 17.9 17.5
9 19.9 19.5 19.0 18.6 18.2 17.8 17.4 17.0 16.6
8.5 18.8 18.4 18.0 17.6 17.2 16.8 16.4 16.0 15.6
8 17.7 17.3 16.9 16.6 16.2 15.8 15.5 15.1 14.7
Litters/sow/year = 2.3
Preweaning Mortality, %
Born Alive 4 6 8 10 12 14 16 18 20
12 24.2 23.7 23.2 22.7 22.2 21.7 21.2 20.7 20.2
11.5 23.2 22.7 22.2 21.7 21.3 20.8 20.3 19.8 19.3
11 22.2 21.7 21.3 20.8 20.3 19.9 19.4 18.9 18.5
10.5 21.2 20.7 20.3 19.8 19.4 19.0 18.5 18.1 17.6
10 20.2 19.7 19.3 18.9 18.5 18.1 17.6 17.2 16.8
9.5 19.2 18.8 18.4 18.0 17.6 17.2 16.8 16.4 16.0
9 18.1 17.8 17.4 17.0 16.6 16.3 15.9 15.5 15.1
8.5 17.1 16.8 16.4 16.1 15.7 15.4 15.0 14.6 14.3
8 16.1 15.8 15.5 15.1 14.8 14.4 14.1 13.8 13.4
Litters/sow/year = 2.1
Table 3. Effect of AI Technician (256 sows/technician) on Reproductive Throughput
Technician Farrowing Rate (%) # Born Alive/Litter Total # Born/Litter # Pigs Produced
1 90.6 10.3 11.0 2,348
2 85.9 10.5 11.2 2,310
3 81.6 10.3 11.0 2,153
4 89.1 10.2 10.8 2,346
5 89.8 10.4 11.1 2,413
6 67.8 8.5 9.3 1,377
Flowers, 1993
Table 4. Effect of AI Technician Fatigue on Reproductive Throughput
Matings/Day Technician (n) Farrowing Rate (%) Born Alive
1-5 24 86.7x 10.7
6-10 54 85.2x 10.5
11-15 59 78.3x,y 10.3
>15 39 71.4y 10.3
SEM 5.2 0.3
x,yValues in the same column with differing superscripts are significantly different at P < 0.05.
Flowers, 1996

How to Reduce Seasonal Infertility

The seasonal decrease in sow fertility during the summer and early fall is a common and costly phenomenon on many farms, and can contribute greatly to variability in numbers of pigs produced. From July to September, sows take longer to return to estrus after weaning, have reduced ovulation rates and a higher incidence of anestrus than at other times of the year. Sows mated during this period often exhibit a 10% decrease in farrowing rate and sometimes a 0.5- to 1.0-pig decrease in litter size.

The following steps can reduce the impact of seasonal infertility.

  • Incorporate the most advanced methods of ventilation and cooling into all phases of gilt development and sow productivity, and make sure they work. Don't wait until sows and gilts are already heat stressed. Activate systems earlier to periods of prolonged, high-ambient temperatures.

  • Schedule animal activities in the early morning and evening, when temperatures are not as extreme. This practice benefits both employees and breeding females.

  • Set up a cool zone (reduced heat index) for the gilt acclimation phase.

  • Implement strategies to reduce or avoid sow movements and mixing. Reevaluate estrous detection strategies to ensure optimal reproductive stimulation, and that insemination protocols are used to avoid late estrual inseminations.

  • Evaluate specific problems (i.e., anestrus or prolonged wean-to-estrus interval) and apply hormonal treatments when needed.

  • Feed nursing sows smaller quantities of more nutrient-dense diets more often.

  • Overcompensate for an increase in seasonal anestrus by having 10 to 15% more gilts available for breeding. However, avoid overcrowding of additional gilts.

  • Consider implementing an early-wean/split-weaning program during the summer that will reduce the metabolic demand on lactating females.

  • Utilize genetics that have documented records for superior appetite and feed intakes.