There are two basic options for acquiring the replacement gilts needed to sustain a commercial sow herd — purchase from a genetic supplier or develop an internal multiplication program.

In recent years, efforts to minimize the risks of introducing new disease vectors — particularly porcine reproductive and respiratory syndrome — have led many producers to raise their own replacement gilts.

It is important to understand the pros and cons of producing vs. purchasing replacement gilts. When a producer chooses to purchase replacement gilts, the genetic supplier is responsible for genetic improvement. In a sense, the producer uses capital (purchase price + royalties) to offset the cost of managing a genetic improvement program.

With internal multiplication of replacement females, commercial producers must set aside a portion of their labor, management and facilities for that purpose. Although a portion of the genetic improvement will still come from outside sources, such as maternal line boar semen to maintain the pure line females, there is a good deal of management and labor required to effectively maintain an internal multiplication program.

If a herd uses a great grandparent (GGP) or a grandparent (GP) program, pure lines must be maintained in the breeding herd. The percentage of each will vary, depending on the number of replacement gilts needed. It is critical that the pure line females are identified and mated for the sole purpose of producing highly prolific replacement females.

When the GGP or GP females farrow, it is essential to identify their female offspring so they can be tracked throughout their growth and development.

Most internal multiplication systems rely on their genetic supplier to select for and improve growth rate and backfat traits to alleviate the need to weigh and scan each candidate gilt as they approach puberty. Generally, replacement gilts should be in the top half of their contemporary group in terms of growth rate, and around 0.75 in.
of backfat at market weight (~250 lb.) and near 1 in. at mating (300 lb. or heavier).

Once the largest gilts are identified, the next step is to evaluate every female for feet, leg and structural soundness, checking closely for injuries. In addition, candidate gilts must be screened for reproductive trait soundness — vulva size and shape and underline (teat) quality.

When this initial screening is complete, roughly 70-75% of the gilts will be ready to enter the development phase.

Some commercial producers prefer to develop replacement females using a two- or three-breed rotational crossbreeding system. The first step to these programs is identifying and mating the most productive sows in the herd to maternal line boars, often brought in via semen. These breeding programs require good records on key maternal traits — number born alive, number and weight at weaning, etc. — plus the ability to track lineage (family tree). Candidate replacement gilts from these superior females must be identified so they can be tracked, evaluated and selected.

If a rotational breeding program is used, a small reduction in heterosis can be expected in the maternal line females. The heterosis loss depends on the number of breeds in the rotation. In a two-breed rotational cross, about 30% of the heterosis is lost; in a three-breed rotational crossbreeding system, about 15% of heterosis is sacrificed.

For additional information on the basic concepts of genetic improvement, breeding and selection programs, selection indexes, recordkeeping requirements and economic considerations, see the 15 fact sheets listed on the National Swine Improvement Federation Web site: http://www.nsif.com/Factsheets.html.

Gilt Development

After gilts have been screened for feet, leg and maternal trait soundness, gilts are moved to the development stage. Nutrition and health programs and estrous stimulation methods for the development phase are discussed elsewhere in this issue.

Not all gilts entering the development phase will cycle, conceive and produce a litter. Roughly 10% of select gilts will drop out before completing their first gestation period. This brings the percentage of gilts from an internal multiplication program entering the breeding herd down to approximately 60-65%.

It is easy to see how an internal gilt multiplication system could fall short of the replacement needs in the breeding herd at certain times of the year. For that reason, I recommend that the internal gilt development system be sized for the time of year when the most gilts are needed — typically during the summer months. With this approach, an adequate supply of gilts will always be available, and there will be some months when greater selection pressure can be turned up a notch.

Less Obvious Costs

Some additional costs of the internal gilt multiplication system are less apparent. For example, the percentage of the sow herd devoted to producing replacement females, typically 8-12%, will reduce the output of market hogs sold from the operation. Compounding the issue, the barrows from the maternal line litters are less valuable than the terminal market hogs in the operation. This can add up to substantial cost.

Assume the maternal line females produce 10 market weight pigs/litter, half are barrows and half are replacement gilt candidates. The barrows are likely worth $10-20 less than their terminal market hog counterparts in the operation — a $50 to $100 loss (cost) per litter.

There are two basic options for acquiring the replacement gilts needed to sustain a commercial sow herd — purchase from a genetic supplier or develop an internal multiplication program.

In recent years, efforts to minimize the risks of introducing new disease vectors — particularly porcine reproductive and respiratory syndrome — have led many producers to raise their own replacement gilts.

It is important to understand the pros and cons of producing vs. purchasing replacement gilts. When a producer chooses to purchase replacement gilts, the genetic supplier is responsible for genetic improvement. In a sense, the producer uses capital (purchase price + royalties) to offset the cost of managing a genetic improvement program.

With internal multiplication of replacement females, commercial producers must set aside a portion of their labor, management and facilities for that purpose. Although a portion of the genetic improvement will still come from outside sources, such as maternal line boar semen to maintain the pure line females, there is a good deal of management and labor required to effectively maintain an internal multiplication program.

If a herd uses a great grandparent (GGP) or a grandparent (GP) program, pure lines must be maintained in the breeding herd. The percentage of each will vary, depending on the number of replacement gilts needed. It is critical that the pure line females are identified and mated for the sole purpose of producing highly prolific replacement females.

When the GGP or GP females farrow, it is essential to identify their female offspring so they can be tracked throughout their growth and development.

Most internal multiplication systems rely on their genetic supplier to select for and improve growth rate and backfat traits to alleviate the need to weigh and scan each candidate gilt as they approach puberty. Generally, replacement gilts should be in the top half of their contemporary group in terms of growth rate, and around 0.75 in.
of backfat at market weight (~250 lb.) and near 1 in. at mating (300 lb. or heavier).

Once the largest gilts are identified, the next step is to evaluate every female for feet, leg and structural soundness, checking closely for injuries. In addition, candidate gilts must be screened for reproductive trait soundness — vulva size and shape and underline (teat) quality.

When this initial screening is complete, roughly 70-75% of the gilts will be ready to enter the development phase.

Some commercial producers prefer to develop replacement females using a two- or three-breed rotational crossbreeding system. The first step to these programs is identifying and mating the most productive sows in the herd to maternal line boars, often brought in via semen. These breeding programs require good records on key maternal traits — number born alive, number and weight at weaning, etc. — plus the ability to track lineage (family tree). Candidate replacement gilts from these superior females must be identified so they can be tracked, evaluated and selected.

If a rotational breeding program is used, a small reduction in heterosis can be expected in the maternal line females. The heterosis loss depends on the number of breeds in the rotation. In a two-breed rotational cross, about 30% of the heterosis is lost; in a three-breed rotational crossbreeding system, about 15% of heterosis is sacrificed.

For additional information on the basic concepts of genetic improvement, breeding and selection programs, selection indexes, recordkeeping requirements and economic considerations, see the 15 fact sheets listed on the National Swine Improvement Federation Web site: http://www.nsif.com/Factsheets.html.

Gilt Development

After gilts have been screened for feet, leg and maternal trait soundness, gilts are moved to the development stage. Nutrition and health programs and estrous stimulation methods for the development phase are discussed elsewhere in this issue.

Not all gilts entering the development phase will cycle, conceive and produce a litter. Roughly 10% of select gilts will drop out before completing their first gestation period. This brings the percentage of gilts from an internal multiplication program entering the breeding herd down to approximately 60-65%.

It is easy to see how an internal gilt multiplication system could fall short of the replacement needs in the breeding herd at certain times of the year. For that reason, I recommend that the internal gilt development system be sized for the time of year when the most gilts are needed — typically during the summer months. With this approach, an adequate supply of gilts will always be available, and there will be some months when greater selection pressure can be turned up a notch.

Less Obvious Costs

Some additional costs of the internal gilt multiplication system are less apparent. For example, the percentage of the sow herd devoted to producing replacement females, typically 8-12%, will reduce the output of market hogs sold from the operation. Compounding the issue, the barrows from the maternal line litters are less valuable than the terminal market hogs in the operation. This can add up to substantial cost.

Assume the maternal line females produce 10 market weight pigs/litter, half are barrows and half are replacement gilt candidates. The barrows are likely worth $10-20 less than their terminal market hog counterparts in the operation — a $50 to $100 loss (cost) per litter.