Pig reproduction is an adventure for most new swine enthusiasts. Often, the excitement of fruitful events, such as the birth of a litter of many new piglets, is often paired with a frustrating struggle of how to actually bring a gilt into season for her first breeding. In this article, you will find an overview of swine herd management, including typical markers of performance, different breeding and farrowing management systems, puberty (maturity for breeding), and techniques for breeding.
- Measuring reproductive performance
The reproductive herd is for the multiplication of maternal and paternal lines that are prized for economically valuable reproductive traits, or, traits that generate desirable offspring reliably. Typically, prized reproductive traits include litter size, particularly total number of pigs born, and pigs weaned, weight of the litter of piglets at birth and weaning, wean-to-estrus interval (WEI), and pigs per sow per year (PSY). In more recent years, length of time a sow remains productive in the herd (longevity or survivability) is increasing in priority for major genetic lines. These traits are prioritized due to the impact on value of the sow to the herd.
Commonly, these records are collected to measure productivity in the reproductive herd and can be defined as follows:
- Litter size: The number of pigs per litter. As the number of pigs born per litter increases, generally there is an increase in the number of pigs born alive and the number of pigs weaned. This number is currently scrutinized as a primary economic focus, as in recent years there has been evidence of reduced birth weights due to increased litter sizes, which is associated with increased mortality rates and decreased growth rates in offspring. However, in the same period of time, offspring have been selected and now grow at the fastest rate in history, while mortality rates have generally remained the same. Litter size remains a top priority for most pig producers.
Total born, born alive: Total born is the total number of pigs a sow has, including born alive, stillborn, and mummies. The number born alive is all piglets born alive, excluding number of pigs born still (stillborn, fully developed but not alive at birth) and mummies (partially decomposed due to death early in gestation and before full development).
- Total Weaned: The total number of pigs an individual sow weans. Marker of sow's ability to provide enough milk and mothering ability to rear pigs.
- Birth and Wean weight: Birth weight is the weight of piglets born alive within the first 24 hours, typically, this includes all piglets that were born alive, even if some of those pigs died before weighing. Wean weight is the weight of the piglets that were weaned from one litter. Weights can be individual, but are usually collected by producers as an entire litter.
- Wean-to-Estrus Interval (WEI): the amount of time that passes from the time a litter is weaned from a sow to the time she returns to estrus. A good sow should be reliable in her ability to return to a productive heat or estrus in a timely manner post weaning (usually 4-6 days). It is very common for producers to give sows up to 7 days post weaning to show signs of estrus. After 7 days, the opportunity to catch a reliable heat is usually dependent on the sow's ability to enter back into a normal estrous cycle. Depending on your system, you may wait until the next cycle (18-21 days) while watching for heat and trying to breed again.
- Heat-No-Service: As explained in the name, a heat or signal of readiness to breed is observed in the sow, however she is not inseminated (bred or 'serviced') by a boar or Artificial Insemination. Instead, she is allowed to continue in the estrous cycle (18-21 days) until her next heat or estrus period is reached. A purposely skipped heat is different than a missed heat. Purposely skipped heat stages are associated with management decisions that are for the benefit of the sow or the system. A missed heat is either a lack of management or a reproductively unpredictable sow; in either case here, a missed heat generally contributes to a poor understanding of herd performance.
- Days Non-Productive (DNP): The number of days that a sow is not in gestation (pregnant), lactation, or the 7-day window post weaning. This number can be used to evaluate overhead cost of caring for sows in the herd and act as a measure of reproductive performance when culling decisions are made or management changes occur.
- Pigs per Sow, per Year (PSY): The number of piglets born per sow in a given period, expressed on a yearly basis, divided by the average herd size at mating. This is often used to broadly evaluate sow productivity within the entire herd and across parities. PSY has traditionally been the benchmark of reproductive efficiency, however current pig production models place less emphasis on this single measurement.
- Longevity: how long a sow stays productive (continues to have litters) in the herd. Longevity of sows in pig operations can and should be measured across a variety of indicators of sow removal, such as replacement rate, culling rate, percent of gilts in the herd, and mean parity (number of litters) of females in the herd. Each marker of removal can indicate a different reason for sows exiting the herd, and should be carefully considered.
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