Know When to Cull and Replace

Refine your practices to maximize production and profits.

By Stephanie Rutten-Ramos

Sow culling and subsequent replacement rates represent economic opportunities for producers. According to PigCHAMP Annual Summaries, sow culling rates have increased over the last 10 years from median values of 43.6% to 48.7% and averages of 45.5% to 47.0%. Sow culling serves two general purposes. First, it is a tool to remove sows with problems related to their health or welfare (i.e., lameness, discharges, etc.). Second, it is tool to replace minimally productive (i.e., failure to conceive, small litter size) and aging females.

While the ability to cull for sow health and welfare is a critical component of good husbandry, the need for such removals may also reflect an opportunity to improve gilt selection, acclimation, sow nutrition and other herd practices.

Culling for performance reasons presents both production and economic opportunities. However, effective production-based culling requires an ability to reliably predict the future performance of a given animal. While production-based culls account for the majority of olderparity removal reasons, in many herds, they also account for approximately half of the removal reasons in the early and middle parities.

Despite perceptions, aggressive production-based culling may not be an economically effective strategy to improve performance. In fact, several studies have identified financial advantages, but not necessarily productivity differences, when herds employ lower culling rates and older parity structures (Kroes and Van Male, 1979; Jalvingh et al., 1992; Lucia et al., 2000; Koketsu, 2007).

The challenge with production-based culling lies in our ability – or inability – to predict the future performance of individual animals. While retrospective record analyses suggest that removals related to small litter size may be advantageous, the benefits of removals related to conception are less consistent (Rutten-Ramos and Deen, 2009).

Figure 1: The evolution of herd parity distribution over time assuming consistent removal rates within parity. (The resultant removal rate generates an average herd parity of 2.9)

Although this is an area for additional research, there may be a few factors contributing to the unreliability of fertility predictions. First, several factors contribute to sow fertility. These include season of the year, sow nutrition, mating timing, frequency of insemination, insemination technique and semen quality, just to name a few. If a decision to cull considers only the number of services and does not account for other influences, sows may actually be culled for factors not related to their ability to conceive. Second, because of the nature of how gilts are introduced to sow herds, aggressive sow culling may be used as a method to make room for incoming gilts. In such circumstances, liberal culling criteria may be employed, thereby weakening the removal/replacement outcome. And third, when a herd is experiencing a general challenge with conception, gilts do not tend to fare better than sows with respect to overall fertility and longevity.

Another important consideration with respect to sow culling is its impact on herd parity distribution. And while it may be conceptually simple to compare the singleparity performance of a sow to the expected first-litter performance of an “average” replacement gilt, the true productivity (and economic) comparisons are not that simple. If the determination of when to keep and when to cull a sow seeks to optimize the economic value of the sow space, then sow survival must also be considered. For example, fourth parity sows have a higher probability of achieving five parities than do the parity one sows which have yet to survive through parities two, three and four. And the incorporation of sow survival into removal decisions may warrant different culling standards as sows age.

Furthermore, parity structure evolves over time according to removal rates within parities (Figure 1.). If a herd employed a consistent within-parity removal rate over time, it would find that the natural changes in parity distribution generate periods of greater and lesser productivity, especially in the first few years.

By understanding the factors that contribute to sow culling, as well as the consequences of sow culling decisions, herds can refine their practices to generate both economic and production advantages.

Editor’s Note: Stephanie Rutten-Ramos received her DVM and PhD from the University of Minnesota and is an independent consultant. To contact her, e-mail: rutt0011@ umn.edu