Introduction

The demand on commercial pork producers to raise leaner animals without compromising reproduction or productivity dictates that a terminal crossbreeding program be used. A terminal crossbreeding system allows the producer the best use of specialized sire and dam lines. Terminal sire lines should be used that are extreme in leanness, muscling and growth. Emphasis should be placed on litter size, milking ability and longevity within the dam lines, with some regard to backfat.

By using sire and dam lines that differ completely in breed composition maximum paternal, maternal and individual heterosis will be achieved. A terminal crossbreeding system also allows the producer to have maximum consistency in the final product, uniformity of production practices and less labor in the breeding barn.

The problem in a terminal crossbreeding program is obtaining replacement gilts. There are two options. They can be purchased or raised on the farm.

Why purchase?

Producers decide to purchase gilts for many reasons. The greatest advantage to many producers is the opportunity to purchase animals of greater genetic value from a higher quality selection program. For other producers herd size may be too small to maintain a separate breeding group to produce gilts.

For some, the only way to obtain some breeds or lines is by purchasing the terminal breeding animals. For other producers, using a single seedstock supplier that has high herd health can allow the establishment of a herd health level equal to that experienced by the supplier.

Perhaps the most common reason that producers purchase gilts is "service". Service generally means that gilts are purchased with a guarantee that they will breed, be available when needed and will be delivered to the farm. Some seedstock suppliers also offer record-keeping services, animal selections and management and nutritional consulting.

Why produce?

Most producers who raise their own replacement gilts are trying to reduce their total investment in breeding stock. Other producers may be trying to minimize the health risk associated with bringing in new animals to the herd. It is also possible to create capital gain opportunities on cull sows when you produce your own replacement gilts.

Requirements for a Successful Production Program

The five basic ingredients for a good replacement gilt production program are: 1) Management, 2) Planning, 3) Record-keeping, 4) Desire, and 5) Money. A producer that is raising replacement gilts should be able to answer yes to the following questions.

1. Are you a good manager?
2. Can you operate two production systems in one operation?
3. Do the little details receive attention?
4. Are all breeding animals identified individually?
5. Do you have a systematic breeding plan?
6. Will your production schedule allow for timely production of replacements?
7. Are the breeds or lines in your program readily available?
8. Do you follow a complete performance testing program?
9. Are your records computerized and current?
10. Are lifetime production records on each sow complete?
11. Do you take litter weights on time?
12. Do you chart and study performance trends?
13. Do you enjoy making the selections?
14. Do you take the time to locate genetically superior herd sires?
15. Do you use performance records?
16. Are you willing to pay extra for grandparent stock?
17. Is your operation large enough to take full advantage of genetically superior sires?

Costs to Raise Replacement Gilts

The primary costs associated with gilt production can be separated into four categories. When you produce gilts a portion of the herd is dedicated to matings that will reduce heterosis. Purchase of boars and some gilts may still be needed. Even though fewer need to be purchased, these animals should be of greater genetic merit and will be priced higher. Also, the extra time required to properly manage gilt production has a cost. Extra time spent in management is required for purchasing germplasm, performance testing, specialized mating and record keeping. The final cost associated with gilt production is lost market hog value on cull gilts and littermate barrows. The lost market hog value will be greatest in a carcass merit buying program.

Production Programs

Three different methods of making a four breed terminal cross will be compared. The first system is where all breeding animals are purchased and the second is a grand parent herd. The third system is a rotaterminal approach where the high producing sows are identified and mated to maternal boars to produce gilts.

Purchase: In this system both F1 sows and F1 boars to produce the market crosses are purchased. Tables 1 and 2 show that maximum heterosis levels are maintained under this system. Table 3 shows that purchasing gilts returns the greatest profit per 100 sows. However, in Table 4 it is obvious that this system requires the greatest investment in breeding animals. In contrast there is no additional management cost (Table 5) or lost market hog value (Table 6).

Grand Parent: In this system 15% of the sow herd is dedicated to the production of gilts. Tables 1 and 2 show that this will result in a 15% loss of maternal heterosis which reduces profit by $512 per/100 sows (Table 3). The investment in breeding stock is intermediate because a higher price is paid for grand parent boars and gilts that have greater genetic potential. There are also additional costs for managing a separate grand parent herd (Table 5) and $1,644 of market hog value will be lost (Table 6) in a carcass merit program due to cull "maternal" gilts and barrows.

Rotaterminal: In this system 15% of the sow herd is also dedicated to gilt production. The accurate identification of the top 15% of the sows is vitally important to make this system work. Tables 1 and 2 show that the greatest reduction in heterosis occurs in this system. The profit (Table 3) is $1,144 less than the grand parent system and $1,656 less than the purchase program per 100 sows. However, the rotaterminal system is expected to have the lowest cost of germplasm (Table 4). Management costs (Table 5) are the greatest with this system and there is lost market hog value (Table 5) on a carcass merit program.

Table 7 shows the comparative net return for each program when profit, cost of germplasm, cost of management and lost market hog value are considered. The net return has a range of only $299 per 100 sows. The small differences in net return indicate that deciding which gilt production system to use is primarily a management decision.

An important assumption that was made is that genetic merit is considered to be equal in all three systems. If genetic merit is not equal, the system that offers the greatest genetic potential will have the greatest net return. The program that has the greatest risk of reduced genetic potential is the rotaterminal if the sow herd used for producing replacements is not of high genetic merit. In the rotaterminal program great care must be used to bring in the absolute best in maternal boars to produce replacement gilts.

Summary

You should consider raising your gilts if:

• Your herd is 100 sows or larger.
• You have a complete record-keeping system.
• Your have adequate space in your facilities.
• You have the talent and labor required.
• You are willing to invest in grand parent stock.
• You ENJOY it.

• You like the service and convenience.
• Your seedstock supplier is making rapid genetic progress.
• You like a simple breeding program.
• You do not have the facilities for a specialized program.
• You do not have the labor for specialized breeding.
• You cannot risk the investment in grand parent stock.
• You need a quick turnover of your herd.

Reviewed by:
Darwin G. Braund, Chrales M. Stanislaw, Department of Animal Science,
and Kelly D. Zering, Department of Agriculture and Resource Economics, North Carolina State University.

Since June 1, 2000