1 This value needs to added to 100 to obtain the NSIF index of the progeny of the selected boars and gilts.

It is important to realize that genetic lag is not only important when genetic improvement is taking place at the nucleus level. From Figure 2 (PIH-9) the importance of evaluating seedstock suppliers was described, it should also be noted that the difference between the commercial herds and the seedstock suppliers is the genetic lag. The structure of the genetic transfer system will determine how wide this gap is between the seedstock supplier and commercial producers.

At the multiplier level the most common system follows the three tiers where replacement boars and gilts come to the multiplier level from the nucleus and the multiplier subsequently provides replacement boars and gilts to the commercial operations. Every additional multiplication step that is added to the system moving the commercial boar and gilt replacements further from the genetic improvement program at the nucleus level increases genetic lag.

Most multiplier herds are operated in typical commercial fashion with standard replacement rates. Selection is usually not performed among the crossbred progeny at the multiplier level because of the large proportion of females required and the increased genetic cost that it would create. Genetic improvement is made at the multiplier level by routine replacements from the nucleus level where continuous genetic improvement is occurring. Genetic lag can be addressed at the multiplier level through selection of boars.

It is generally not cost effective to operate a selection program at the commercial level. However genetic lag can be reduced by regular replacement of breeding stock with superior individuals and boars can be replaced at an average age of one year to minimize genetic lag. The opportunity to reduce genetic lag at the commercial level is in the quality of seedstock selected. It is possible to purchase boars of superior genetic merit directly from the nucleus level and this can reduce genetic lag by about 1/2 year.

AI can reduce genetic lag in two primary ways:

1. When AI is used the boar:sow ratio will decrease reducing the number of boars needed allowing fewer, superior boars to be selected.
1. AI offers the opportunity to reduce genetic lag by using superior sires from the nucleus level at all levels of the production pyramid.

Using AI at any level of the pyramid can reduce genetic lag by approximate 1/2 year depending on the selection intensity placed on natural service and AI boars. If AI is used at all levels of the production pyramid and gilts are obtained from a source with consistent genetic improvement the genetic lag can be reduced to its lowest possible level of about 3 1/2 years.

For commercial producers to reduce genetic lag the most attention should be paid to the selection of the seedstock supplier. The seedstock supplier must be realizing genetic progress through the use of a performance testing and genetic evaluation program and then rapidly disseminating this improvement through its multiplication system. The commercial producers then must use genetic information when purchasing breeding animals along with acceptable health, reproductive soundness, and skeletal structure. Incorporation of an AI program will also greatly reduce genetic lag if the AI boars that are selected come from the nucleus level. If no change is made in the way that commercial boars are selected genetic lag will not be changed. And finally by reducing the time that commercial boars are used to 1 year of less will result in a reduction in genetic lag.

Genetic cost of production is influenced by the structure of the breeding herd which is driven by the choice of crossbreeding system and the genetic merit of the boars and gilts used. One of the first steps is deciding whether replacement-breeding animals will be generated by the producer or purchased from outside sources. Although more and more producer have turned to purchasing replacement gilts from commercial seedstock suppliers, many still produce their own. Arguments can successfully be made for either approach. As pork producers realize the value of more precise genetic programs, much of their attention has turned to buying or producing specific maternal lines and gaining access to specific terminal sires that will push them towards greater market premiums. The following quick cost comparison pinpoints some to the facility, equipment and labor difference between 'semen delivery systems' which is a component along with replacement female systems in genetic cost of production. The procedures to evaluate these genetic costs of production are the same for all sizes of operations, but there are efficiencies of size.

The semen delivery system is simply the type of service that is used for mating. Common semen delivery systems are natural - pen mating, natural - hand mating or artificial insemination (AI). The number of boars will be dictated by the structure of the sow herd and the semen delivery system. To compare genetic costs the information that is needed is the cost of the boars, their salvage value, annual replacement rate, maintenance cost and insemination cost.

In the following cost examples for natural service and AI mating programs price quotes provided by Minitube of America (10/3/95) were used to determine AI equipment costs. The fixed costs for purchase price of the boars were estimated to be $800.00 for natural service boars with 3 years of use, on-farm AI boars cost $2500.00 and were used for 2 years, and boars for a small stud cost $5500.00 and were used for 2 years. Variable costs for boar maintenance were estimated to be $.75 per boar per day. The boar to sow ratio was 16:1 for natural service, 107:1 for On-farm collection and 250:1 for the small stud. It was also assumed that sows were mated an average of 2.1 times/year. The estimates for labor required per mating are from Flowers (1992) and a labor cost of $10.00 per hour was assumed for both mating and semen collection and processing.

Table 4 indicates that AI has a considerable cost savings over natural service. If on-farm semen collection and processing is used rather than purchased semen another large savings can be realized per sow. For on-farm collection and processing there is a cost savings relationship with the size of operation.

The application and use of AI on commercial swine farms offers significant opportunities for increasing profits. Cost savings and additional revenue can be generated by AI from two sources: reduction of costs associated with boar maintenance and increased receipts for market animals due to superior genetic merit. However, in the above examples genetic merit was not evaluated in the cost savings of the mating programs. In addition, the successful implementation of AI is dependent on the management skills of the breeding technician. If the proper estrous detection, insemination and processing procedures are not followed reductions in profit could result from the use of AI.

Figure 4. Example of disconnected herds and sires.

Figure 5. Example of connected herds and sires.

A second way that AI improves accuracy is by making it very easy for small herds to produce pigs by several sires within a contemporary group. An outside sire will not only provide a basis for comparision, but will also tie that herd to other within a breed. The accuracy values associated with EPDs will increase when more herds are represented with progeny and if the progeny are uniformly distributed across herds.

A popular breeding system among producers raising their own replacements gilts is the rotaterminal system. In the rotaterminal system the best producing sows are bred to boars superior in maternal traits to produce replacement gilts. The remainder of the sow herd is bred to terminal boars which differ in genetic make-up from the sows. The rotation of the maternal boar breeds is in a predetermined order so that the amount of breed in common with the sow is minimized. Generally 15% of the sow herd is devoted to producing replacement females.

In a three breed rotational system the maximum heterosis that can be achieved is 86%. To achieve maximum heterosis it is conceivable that three maternal breeds of boars may be required in a single breeding period to ensure that each top ranking sow is mated in the optimum breed sequence. This may result in boars being used at least that optimum efficiency. By implementing AI to produce these litters not only could the optimum breed be used for each selected sow but also boars with extremely high EPDS could be chosen. The exact number of doses of each kind of semen could be determined at the time the sows are ranked and the semen ordered in advance of needs.

When determining the replacement female system and the semen delivery system it is important to ask; What do I want to do? and What can I do?. In order to make the best decision the cost and inputs required for each option must be understood and weighed with the value of increased genetic merit associated with each system. Before making a decision to bring a component of the genetic system, such as, gilt multiplication or a boar stud to the farm evaluate the potential for the five basic ingredients of successful genetic systems: 1) Management, 2) Planning, 3) Record-keeping, 4) Desire, and 5) Money.

To make genetic improvement in a herd, use performance evaluated seedstock selected from at least the upper 50% of boars and 75% of gilts in a herd that is realizing genetic progress through the use of a performance testing and genetic evaluation program. Commercial producers should require seedstock suppliers to follow a sound genetic improvment program and then use genetic information when purchasing breeding animals along with acceptable health, reproductive soundness, and skeletal structure.