Achieving 30 Pigs/Sow/Year

Key differences exist in high producing farms.
By John T. Waddell

In North America, we have come to respect the Danes for their extremely disciplined approach to pig production but have at the same time tended to discount some of their outstanding production figures due to the fact that these were typically small farms. Regardless of geographical location, we all operate under the same constraints when it comes to reproductive efficiency. If “pigs weaned per female per year” is the measure we choose to employ, then the productivity tree has the same components (Figure 1).

Since gestation length cannot be readily manipulated and shortening lactation length has detrimental effects on subsequent litter size, the number of litters per female per year is less likely to be the branch of the productivity tree that yields the greatest potential improvement in pigs weaned per female per year. The seemingly largest potential to increase the number of pigs weaned per female per year comes in the weaned per litter branch (Polson, 1992).

The economic feasibility of “chasing” the 30 pigs per sow per year goal has been questioned in the past. For example, what is the value of weaning 30 pigs per sow per year if the quality and performance of those pigs is demonstrably inferior to pigs weaned from a less aggressive approach in the overall economic performance of the production system? The Danes recognized this dilemma as they selected for larger and larger litter size and then shifted the emphasis of selection for survivability at five days of age (Su et al., 2007).

The quest continues to maximize reproductive performance while optimizing the quality, size and performance of the pigs weaned. This article will identify the obstacles to achieving 30 pigs per sow per year and show how innovative producers and their advisors are overcoming these obstacles.

It should be obvious that there are no short cuts or quick fixes that will suddenly jump a farm's production to these high levels. In a similar vein, it is unlikely that any single management change would make a huge difference on a farm that is not committed to other important aspects and practices. In other words, it is unlikely that these techniques can be "cherry picked" or applied piecemeal to get expected results. In the end, dedication and discipline in execution of hundreds of daily details allow farms to reach and achieve formerly unimaginable levels of production.


The industry has made huge strides in selection for large litter size. Fourteen pigs total born is becoming commonplace with one benchmarking database reporting the top 5% of over 600 farms with a potential for over 35 pigs born per mated female per year. This calculates to over 14.5 pigs born per female farrowed. (Rix and Ketcham, 2009) Even the top 10% of this database is above 14 total born per litter (Figure 2).

Figure 2. Genetic potential for litter size – total born/mated female/year

While the influence of European genetics are being seen in North America, some of the selection programs have continued to select for litter size with annual improvements of over a quarter of a pig per litter per year. New methods of genomic selection have led some to predict additional gains in litter size over the next decade to achieve live born averages topping 19 pigs per litter (Rathje, 2009).

Of course, huge gains in litter size have not come without a cost. As the Danish industry pushed up litter size to 14 and beyond, they discovered an increase in variation within litters with the number of small, less viable pigs creating challenges for survivability. Researchers discovered that by selecting for the number of pigs remaining alive at five days of age, they could indirectly select away from smaller, less viable pigs and improve piglet survivability throughout lactation (Su et al., 2007). Since selection for this trait began in 2004, the Danes have demonstrated an improvement of nearly two pigs per litter at five days of age. Maximizing heterosis by utilizing an F1 crossbred female is essential for capturing maximum genetic potential.

Gilt Development

Gilt development may account for some of the biggest improvements in production the North American industry has reaped in the previous five years and has often been the most neglected on many farms. With culling rates of 30-50%, gilts may represent nearly a fourth of all litters. Even minor improvements in gilt productivity can substantially impact the reproductive performance of the entire herd and the longevity and productivity of the individual female. In attempts to keep non-productive days at a minimum by breeding gilts younger, we have inadvertently reduced both their litter size and longevity in many cases. A happy medium has been reached by allowing gilts to reach at least 300 lbs. live weight or 240 days of age prior to mating. Gilts should never be bred on their first estrus cycle but there appears to be little or no economic advantage to waiting beyond the second or third cycle for their first mating.

Gilt isolation and acclimatization are an essential part of every production system. Gilts should be housed in pens or stalls allowing approximately 13-15 sq. ft. per animal. Contrary to practices in North America, a common practice in Denmark is to limit (actually eliminate) boar exposure at any time in the gilts life prior to actually mating. There is no boar exposure! Heat checking is predominately performed visually via outward signs of estrous. Surprisingly, even back pressure is used sparingly. They simply walk behind the gilts that are housed individually and look for swelling and redness of the vulva.

As cycling gilts are detected, the caretaker chalks or color sprays their back to create a color coded mark. Three colors are used to identify the gilts in heat and the colors are rotated between the three weeks of the normal gilt cycle. For example, all gilts found in heat in this week will receive a blue mark, next week they will be marked red and the following week green. This marking system allows the breeding manager to select from those gilts likely to cycle in a given week so as to reduce the number of gilts needing to be held at the sow unit prior to mating. Once per week, the gilts that have been marked to cycle within the coming week are moved to the sow unit at the beginning of the week they are to be mated, creating a “just in time” type of flow (Thomsen, 2004).

Age at First Mating

The Danish gilt's age at first mating tends to be at least a month older than what is considered normal in North America. The Danes have shown that there are significant reproductive efficiencies to be gained by waiting until gilts are at least 8 months of age regardless of weight (National Committee Pig Breeding, Health & Production, 1992). Furthermore, this same research demonstrates that the gilts bred later in life have significantly more live pigs in their second litter when compared to the "early" mated gilts. On some high producing farms in Denmark, the oldest gilts in the pool are actually nearing 11 months old at first mating with average age being near 9 months!

As for weight at first mating, it is not uncommon for gilts to be upwards of 350 lbs. and some Danish producers seem unconcerned with allowing the gilts to become too large or old. More typically on high producing farms, the gilts usually are 300 to 330 lbs. at first mating. Danish gilts tend to be older and carry more back fat to endure five weeks of lactation and still be expected to return to heat and have an increased litter size in their second litter.

To enable an older age at first mating, the farm must build "slack" into the gilt isolation and acclimatization facility to make it possible to skip heats on younger animals when larger numbers of females are needed in any given week. To avoid "holes" in production, the urge is to mate younger and younger gilts. By allowing additional space in the gilt development units and maintaining a larger inventory of breeding aged gilts, the producer is not tempted to dip into the younger gilt pool for the sole purpose of meeting a weekly breeding target (Thing, 2004).

Challenging First Litter Gilts and Lactation Length

One of the most unique production management tools used in Denmark is how they challenge first litter gilts. Management strongly believes that unless gilts are “challenged” to produce strongly at first parity, these females will be less productive throughout their lifetime. The farrowing personnel aggressively uses cross-fostering early in the piglet’s life to bring all gilt litters to 13 piglets. These top farms average over 14 pigs born alive per litter, allowing the farrowing manager leeway in adjusting the number of piglets each gilt and sow nurses. While the gilts always receive 13 piglets on day one, sows are typically only given 12 pigs to nurse

What happens to all the extra piglets from a farm averaging over 14 born alive? The average weaning age for the entire farm was around 24 days. Parity 2 (and higher) sows are only lactated for about 21 days and are then weaned. Gilts on the other hand, are allowed to nurse their first litter for the about three weeks and then “their” pigs are weaned with others of the same age (21-24 days). Then, instead of discontinuing the lactation of the first litter gilts, they are left in the farrowing stall and are given another litter made up from piglets at the end of their first week of age. These litters are transferred intact from second litter sows. The second litter sows, in turn, receive piglets from various litters of older sows replacing the litter that was nursed off to the gilts whose litters were weaned.

The end result is that all pigs are weaned around three weeks of age but all the first litter gilts lactate for almost five weeks, weaning not only their own litter but a second litter transferred from a parity 2 sow. This is the essence of “challenging” the gilts (Jensen, 2004).

The longer lactation lengths in Denmark also lead to larger litter sizes on subsequent litters. One rule of thumb is that for each additional day of lactation, the litter size increases on the subsequent litter by 0.1 pigs. The biology of this phenomenon has yet to be clearly understood but a recent increase in weaning age in the United States appears to coincide with increases in litter size.

Inventoried Female to Farrowing Stall Ratio

Denmark has another unique situation regarding farrowing space - they have lots of it! Having never made the transition to early weaning, many producers maintained the existing farrowing stalls when they expanded, and these became the extra spaces needed to challenge first litter gilts. New facilities are built with older weaning age in mind and thus have an abundance of space versus what we typically see in North America. Where the typical three-week weaning age farm in North America has a ratio of 6.25 inventoried females per farrowing stall, it is not unusual to find ratios of less than 4.5 inventoried females per farrowing space in Denmark. Some farms have created a “just in time” flow with the gilts since they enter the sow herd only in the week they are expected to be in heat, which tends to deflate the ratio somewhat. The low sow inventory to farrowing stall ratio offers them a unique opportunity to adjust wean age to fit their desired lactation length, and is thus less dependent on the breeding target.

As for breeding targets, the Danes routinely create farrowing targets utilizing a 90% farrowing rate and since they are required by law to wean beyond 21 days of age, they resist the urge to over-breed.

Culling Policy and Parity Structure

Since the Danes are so driven to excel at producing pigs weaned per sow per year, they are acutely aware of the importance of maintaining genetic improvement and reducing genetic lag. At the farm level on the high producing farms, rarely are sows allowed to remain in the herd after eight litters and generally sows are removed after six litters. Continuous genetic improvement is expected with each generation but since sows peak in production in parity 3 to 5, they target 50% of the inseminated females to be within this parity spread.

Typically, the culling policy is a “two strike” approach. The farm will allow a sow or gilt to remain in the herd (if she is physically sound) beyond one instance of a drop in litter size, but not after a second “strike”. The culling criteria are multi-factorial and include some subjective factors such as temperament or disposition. Generally, sows are expected to produce litters of at least 15 live pigs. They may excuse a sow for a single litter of fewer than 15 if she has other redeeming traits such as good milking ability as evidenced by weaning a large litter of heavy pigs. There are a few exceptions, and each sow and situation is considered on an individual basis. Simply stated, sows are given another chance if weekly breeding targets or her other data deems it necessary (Thing, 2004).

At times the culling decision is made prior to farrowing. The piglets from these sows are used as “extra” pigs to replace the litters of the sows who gave up their litters to the first litter gilts. Approximately 5% of each weekly farrowing group includes sows that will contribute their pigs to other sows and be marked for culling without weaning their pigs. Overall, the Danes practice aggressive culling with the goal of continuous improvement.

The People Factor

The top farms in Denmark employ highly trained, motivated and detail oriented people who are on a mission to exceed 30 pigs per sow per year. Targets for various production parameters are clearly outlined and the current and prior weekly production numbers are prominently displayed. Employees are routinely rewarded for outstanding performance based on the entire farm’s production. If someone hears of a farm that excels in production, they will attempt to emulate it. Veterinarians and consultants are continually challenged to bring new ideas on how to improve production and everyone at the farm has a ravenous appetite for new information (Mikkelsen, 2004).

Farms sustaining 30 pigs/sow/year are commonplace in Denmark, with some reaching 35 pigs/sow/year. Incorporating similar management practices may allow North American producers to achieve these same high levels of productivity.

Editor’s Note:Dr. Waddell, DVM is with the Sutton Veterinary Clinic, Inc. in Sutton, Nebraska. This article is written from a presentation by Dr. Waddell at the 2010 Banff Pork Seminar. For the full text, go to: www.benchmark.farms.com Email the author at: John@suttonvetclinic.com


  • Jensen, H. Personal communication with farm manager of Christiansminde Multisite K/S, Aalborg, DK, June 2004.

  • Mikkelsen, A. Personal communication with veterinary consultant of Christiansminde Multisite K/S. An associate veterinarian with Danvet, Hobro, DK, June 2004.
    National Committee for Pig Breeding, Health and Production, Annual Report 1992. “Mating of Premature Gilts”. p 43

  • Polson, D. Financial Evaluation and Decision Making in the Swine Breeding Herd. Veterinary Clinics of N. America, Nov 1992, 8:3 725- 747

  • Rathje, T. Personal communication, geneticist for Danbred N.A., Oct. 2009

  • Rix, M., and Ketcham, R. Maximize Total Born to Reduce “Per Pig” Costs www.nationalhogfarmer.com

  • Su, G., Lund, M. S., and Sorensen, M. Selection for litter size at day five to improve litter size at weaning and piglet survival rate. J Anim Sci 85:1385-1392

  • Thing, H. Personal communication with farrowing manager of Christiansminde Multisite K/S, Aalborg, DK, June 2004.

  • Thomsen, K. Personal communication with breeding manager of Christiansminde Multisite K/S, Aalborg, DK, June 2004.