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Heterosis and Its Use in Swine Breeding Systems
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Heterosis, or hybrid vigor, is a phenomenon in which the performance of crossbred progeny exceeds the average of the parent animal. It is very evident in lowly heritable traits, such as reproductive efficiency, and therefore is extremely valuable in litter-bearing species such as swine, where reproductive performance plays a major role in profitability. Because effect of heterosis can be easily maximized by proper use of purebred breeding stock, it is a very valuable component of any pork-production system. Proper use of heterosis can improve some measures of reproductive performance, such as 21 day litter weight, by up to 27 percent, and has a positive impact on growth and feed efficiency as well.

The following breeding systems utilize purebred breeding stock in an efficient way to maximize heterosis and therefore profitability in your operation.



Terminal Programs (1 & 2)
In terminal programs, crossbred females, either F1 or three-way cross females, are bred to a purebred terminal boar of a breed not included in the genetic makeup of the female. All progeny are sent to market and no breeding gilts are retained from this final cross; therefore, replacement females must either be purchased or produced in a separate program. This allows the use of purebreds in specialized roles (i.e. to produce only females or only market hogs) and therefore the strong characteristics of each breed can be fully utilized.

Advantages

  • Maintains 100 percent heterosis in both sows and market animals.
  • Provides opportunity to fully utilize each pure breed’s strengths.
  • Produces uniformity of both breeding animals and market hogs, as every animal has the same genetic makeup.
  • System is easy to manage, if replacement females are purchased and all animals produced go to market.

Rotaterminal Program (3)
In the rotaterminal system, two or more breeds are used in rotational cross in order to produce females. Maternal purebred boars are used for replacement gilt production, while the females going into the commercial herd are mated to terminal breed boars, with all progeny going to market. Approximately 15 percent of the sowherd must be committed to female production with the balance (85 percent) used to produce market animals.

Advantages

  • Maintains 100 percent heterosis in the market animals. If three breeds are used in the maternal side, maternal heterosis will be 86 percent; if two breeds are used heterosis will be 67 percent.
  • Provides opportunity to produce replacement females.
  • Produces replacement gilts from top sows, ensuring top maternal performance.
  • Produces uniform market animals, as all are sired by the same breed of boar.