Optimum Length of Time for a Boar to be in Stud

There are typically two conflicting perspectives: that of the boar stud and that of the semen customer, commercial pig producer, according to J.S. Fix and colleagues at North Carolina State University (NCSU) and Pig Improvement Company. They have developed a decision-making tool to determine the optimum length of time a boar should be utilized in an AI program. Their article was published in the November 2008 NCSU Swine News.
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What is the optimum length of time a boar should be in stud? The answer to this question depends on who is being asked the question. There are typically two conflicting perspectives: that of the boar stud and that of the semen customer, commercial pig producer. The objective of this study was to develop a decision-tool that determines the optimum length of time a boar should be utilized in an AI program.

The boar stud wants to increase profit margin by dividing their costs over large amounts of quality se¬men. This typically occurs as boars become older and have higher lifetime semen production. As the boar’s age increases, and thus lifetime semen production increases, many of the costs are divided over a greater number of doses of semen and subsequently costs per dose decrease. The pig producers tend to be on the other end of the boar’s life. They want semen from genetically superior boars. In a successful selection program, this will continually be the youngest boars. The longer a boar is in stud, the more genetically superior his potential replacements become; and thus the pig producer is potentially missing out on an increasingly larger return on their commercial market hogs. Because the two perspectives are on the opposite end of a boar’s life, an optimum must be determined.

Pig Producer’s Perspective

As mentioned, for every week a boar is in stud and is not replaced with a genetically superior boar, there is a value lost for the pig producer. This opportunity lost is calcu¬lated using the following information:

  • Value of an index point for a marketed pig
    • An index is value that is calculated based on a boar’s genetic makeup for various economically important traits
  • Difference in index points between a given boar and a potential replacement
  • Pigs produced per week
    • Pigs marketed per litter
    • Doses per mating
    • Semen production curve
      • Doses of semen per week

Weekly basis is used to account for older boars influencing more pigs.

Boar Stud’s Perspective

For each additional dose of semen produced, the initial costs of the boar are divided over a greater number of doses. The cost per dose is calculated using the following information:

  • Boar stud costs are a function of:
    • Cost of purchasing boar
      • Salvage value of boar
      • Death loss
    • Isolation cost / boar
    • Production cost / boar space / week
    • Collection labor / collection
    • Post collection (lab costs) / dose
    • Royalty cost
      • Per dose
      • Per pig
    • Semen production curve

How to Determine the Optimum?

Figure 1 is a depiction of how the two curves (Boar Stud: cost per week; Pig Producer: opportunity lost per week) change the longer a boar is in stud. The optimum is when these two curves intersect.

Figure 1. Depiction of optimum and how cost and opportunity lost curves change over time.

If an average index value is assumed for the incoming boars to be used as replacements, an index value for which a boar should be culled at a given age can be calculated. This is accomplished by setting the formulas for costs of produc¬tion and opportunity lost equal to one another and solving for the difference in index points. Using the assumed aver¬age index value for replacement boars and the aforemen¬tioned difference in index points, an index value based on weeks in service (or boar’s age) is given. Figure 2 shows an example of index values a boar should be culled at – based on an average incoming index of 100 for various weeks in service.

Figure 2. An example of index value for boars to be culled for a given age when the replacement boars have an average index of 100.

Index Based Boar Stud Culling Tool

A spreadsheet was developed that allows for quick and easy input of boar stud specific inputs that in turn calculates an index level to assist in the replacing of boars in stud with new boars.

All of the values needed to calculate production costs per week and opportunity lost per week are easily entered into the spreadsheet. Some of the inputs, such as average semen production curve and costs, which do not fluctuate much, only need to be updated periodically; however, inputs such as mean of incoming boars or costs which change fre¬quently are easily updated with each use. This tool also can allow for multiple sire lines to be included since production parameters or costs may differ between lines and multiple cost structures. In this example, the royalty cost structure may vary and such can be easily changed. An example of these options is presented in Figure 3. Once the information is put into the spreadsheet, a suggested culling level for a given five-week interval in production is shown. Using an assumed average change in index value due to genetic im¬provement and culling levels for other non-genetic reasons, an average suggested culling age and annual culling rate can be calculated. These values are presented on the same screen as the suggested index culling value (Figure 4).

Figure 3. Example of semi-permanent inputs and inputs for daily use.

Figure 4. Output portion of culling tool

This tool is designed to assist boar stud managers with important culling decisions, by balancing both the boar stud’s perspective and the perspective of pig producers.

December 2008
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