Examine New Traits to Gain Herd Production Efficiency

By Caitlyn Abell, John Mabry, and Ken Stalder

Historically, the majority of the selection emphasis for maternal line selection has focused on number of pigs born alive and 21-day litter weight. While these traits adequately measure overall sow productivity, selection based on these two traits alone would not incorporate sow efficiency evaluation or measurement. Just because a sow can produce a litter with a large number of heavy piglets at weaning, does not mean that she is profitable to the producer. She must be very productive (number born alive, number weaned and weaning litter weight), be consistently productive (return to estrus in less than seven days after weaning, conceive on the mating and farrow a litter 121 days later for every parity), and remain this productive over a high number of parities (at least three, preferably more). Females capable of meeting these requirements will allow a pork operation to be profitable over the long term, assuming market prices cooperate.

Number of litters per sow per year (LSY) is one trait that can be used to improve sow production while also improving sow efficiency. This trait is a measurement of how quickly a sow can produce a litter and begin gestating her next litter. The components of LSY are:

  • Entry-to-first-service interval

  • Gestation length

  • Wean-to-service interval

  • Farrowing rate

  • Farrowing interval

  • Culling-to-removal interval

Opportunities to improve the individual components of LSY vary. Entry-to-first-service interval is herd-dependent and based on the swine operation's management system. For example, some farms enter the replacement gilt into their record-keeping system when they take delivery of a group of replacement gilts, while other producers enter females into the record system when they are bred. The entry-to-first-service interval variability is non-genetic and hence, selection to improve this trait would be ineffective. Gestation length is heritable; however, biology dictates that little variation exists for this trait, which prevents efficient improvement through selection. Typical gestation length is 115 days (three months, three weeks, three days). It can be as low as 112 days and as high as 118 days and still be considered normal. If we attempt to change gestation length through selection, adverse results are likely. If the gestation length is too short, piglets are not fully developed and may not be viable when born. As a result, little, if any, opportunity exists to improve gestation length beyond just a few days and the consistent ability to control gestation length is not likely.

Improvement in the interval from weaning-to-service is also limited by biological constraints. After weaning, sows require a few days to come into estrus before they can be bred. Typically, sows will return to estrus from four to seven days after weaning. Producers need well-developed management practices to ensure proper heat detection. Every sow must be detected in estrus in a timely manner so conception and subsequent farrowing is most likely to occur.

Factors affect farrowing rate

Farrowing rate is affected by both management and genetics. Sufficient variation exists for farrowing rate such that traditional selection may be effective at genetically improving the trait. Improving farrowing rate can in turn improve farrowing interval through indirect selection by reducing the number of non-productive days attained by sows being open.

Consider other factors

Increasing the LSY of the herd by 0.1 can have a major impact on the profitability of the operation. A 0.1 increase in LSY in associated with 11 fewer non-productive days; assuming a cost of $2 per non-productive day per sow, this decrease amounts to $22 per sow per year. A 0.1 increase in LSY also is associated with an increase of one pig born alive per sow per year. This increases revenue by $22 per sow. For a 2,400 sow herd, a 0.1 increase in LSY results in $52,800 in decreased costs due to non-productive days, and an increase in revenue of $52,800 due to more piglets born alive.

It is also important to consider the relationships between LSY and other economically important traits before incorporating LSY into a selection program. Table 1 shows the heritabilities, genetic and phenotypic correlation estimates between LSY, number born alive, wean to estrus, percent lean, backfat and days to 100 kg (220 lbs.). The genetic correlation estimates with LSY are not significant except for the genetic correlation between LSY and weanto- estrus. The correlation between LSY and wean-to-estrus is large in magnitude and favorable. The insignificance of the other genetic correlations suggests that selection for LSY would not adversely affect the other four traits considered.

A Caution

One caution that must be taken when using a calculated trait such as LSY is that simply improving the raw values of the trait may have undesirable consequences. Sows removed immediately after weaning their first parity have an inflated value for LSY. In a system where gilts are brought into the sow herd after they are already bred, these females have not had the opportunity to accumulate any non-productive days. Having a high replacement rate would increase the number of gilts in the herd, and thus, inflate the overall LSY of the herd. A herd that culls an excessive number of gilts immediately after weaning would often have a very acceptable LSY. However, the increased proportion of gilts in the herd would lower overall production because of the productivity differences (number born alive, number weaned and litter weaning weight) and adversely impact any measure of longevity. Ultimately, improving the LSY in a sow operation by having a large proportion of gilts in the herd that are culled after their first litter will decrease production efficiency and reduce an operation's profitability. Gilts don't have the opportunity to fully express their potential for LSY. Because of this; there is no basis for ranking gilts based on their affinity for the trait.

Improving LSY can result in increased herd production efficiency by increasing the number of piglets produced in a year by a single sow. An increase in the number of pigs weaned per female per year can improve herd production efficiency in a similar manner as LSY. Many of the components are the same for both traits. Using production efficiency traits can improve the overall profitability of a pork operation by keeping sows in the breeding herd that can produce large litters of heavy piglets in an optimum amount of time.

Editor's Note:Caitlyn Abell is a graduate student at Iowa State University; John Mabry, PhD; and Ken Stalder, PhD are part of the Department of Animal Science at Iowa State University, Ames, IA.