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Implementation of Terminal Crossbreeding Systems

Terminal crossbreeding systems, both specific crosses, and rotaterminals offer substantial benefits in terms of profit per litter and consistency of the pigs and performance levels. Commercial producers operating terminal crossbreeding systems also can intensify their management, as the genetic composition of the sows and pigs are consistent. Currently, the most common means of producing gilts for independent commercial producers is via contract multiplier herds which seedstock producers establish. Contract multiplier herds can be established and operated efficiently. However, in many cases, establishment of multiplier herds produces conflict. Over time, some multiplier herds want a higher percentage of the replacement gilt premium for their additional expenses and costs. Fluctuations in market hog prices also produce ongoing conflicts. In most cases, multiplier herds are paid a premium on a per-gilt-sold basis. When hog prices are low, 1) gilts don't sell well, 2) multiplier herd gilt inventories increase, 3) good replacement gilts are sold to market at low prices, and 4) the owner of the multiplier herd becomes upset. Then market hog prices go up and commercial producers, previously not purchasing an adequate number of gilts, need a large number of replacements immediately, and thus almost every gilt is selected. This results in a lack of uniform selection and quality control. For these reasons, an increase in the amount of contract multiplier herd production of replacement gilts is not expected.

In terminal crossbreeding systems, replacement gilts are produced in special matings. The high levels of productivity experienced with gilts and sows from these special gilt producing matings give the terminal crossbreeding systems their advantage. Operationally, the production of replacement gilts is the key to the terminal crosses

Herds with weekly schedules should have lower replacement rates, and, in those cases, specific crossbreeding systems would be most profitable. The system returns for Hampshire-Duroc F₁ boar, Yorkshire-Landrace F₁ female specific cross are presented in Table 1. The returns from a specific crossbreeding system are highly dependent on the replacement rate. To determine the percent matings required at the grandparent and great grandparent levels, assumptions must be made as to the replacement rate and the percent of available gilts selected at each level. With lower replacement rates, less gilt producing matings are needed. Assuming a 40% replacement rate per litter farrowed and a 50% gilt selection rate, that is, 2.25 gilts selected per 4.5 gilts raised per litter, the percentages of matings needed of each cross are presented in Table 1. The weighted average for all three tiers, assuming no replacement cost, is $9,556 with 40% replacement rates and $9,999 with 25% replacement rates.

Table 1. Percent matings needed and average systems returns with 40% and 25% replacement rates.

With specific crossbreeding systems, low gilt replacement rates are very important to reduce the number of replacement gilts needed in each tier. The economic impact of low replacement rates in Table 1 (long sow lifetimes) does not take into account the increased reproductive performance in conception rate, number weaned, and unproductive sow days produced by having a higher percentage parity 3-4 females in your herd. The number of 3 and 4 parity females is increased due to lower replacement rates. With typical parity performance levels, number weaned increases .3 pigs per litter and conception rates increase 4% by decreasing replacement rates per litter from 40 to 25%. Thus, it is very important for any producer with high replacement rates to identify management or genetic changes needed to increase sow productive lifetimes.

The question for commercial producers is which method of gilt replacement is more economical and practical? The great-grandparent program involves operating all three tiers. The grandparent program involves purchase of the grandparent gilts to produce the parent gilt. The third option is to purchase the parent gilt. Using typical prices, 25 or 40% replacement rates, and 50% selection rates, the returns for the three options are in Table 2.

Table 2. Returns with two gilt replacement rates and three gilt replacement systems.

The most obvious option is to purchase replacement gilts. The major issue in purchasing replacement gilts is the seedstock cost per litter which is the cost of the gilts above market gilt price divided by the number of litters produced per purchased female. Purchasing gilts of $100 above market price and only achieving 2.5 litters per female (40% replacement rate per litter, approximate 90% annual replacement rate) results in too large of seedstock cost per litter.

The second option is to develop a within-house gilt multiplication system. The very largest producers have within-house great grandparent programs. Great grandparent programs involve the purchase of the maternal great-grandparent gilts which produce extra grandparent gilts. If a Yorkshire-Landrace F₁ is produced, as in Table 1, the great grandparent cross is the production of purebred Yorkshire gilts. The extra purebred Yorkshire gilts are bred to Landrace boars to produce the F₁ Yorkshire-Landrace parent gilts. With this system, an initial purchase of purebred Yorkshire females would have to be for both great grandparent and grandparent tiers. The highest indexing Yorkshires would be mated to purebred Yorkshire boars. In the long term, only high indexing Yorkshire and Landrace boars would need to be purchased or utilized via artificial insemination. In the long term, the great-grandparent systems result in the lowest gilt replacement cost. However, the great grandparent systems also require the most intense management.

An alternative system would to produce a three-breed parent female, i.e. Yorkshire by Duroc-Landrace. Usually this would involve purchasing grandparent Duroc- Landrace F₁ gilts and mating them to Yorkshire boars to produce the three-breed cross parent females. The advantage of this system is two-fold. First, F₁ grandparent gilts are purchased which are more productive, have higher conception rates and longevity than purebred gilts. Second, the three breed parent gilts produced have 100 heterosis and are ¼ Duroc which should make them more rugged.

Operating all three tiers of a terminal crossbreeding system on the same production unit is difficult to manage. Records and animal identification would need to be very complete and accurate. Some producers with two or more production units should seriously consider having one herd with approximately 15% of the total production be responsible for gilt production.

Small producers with 12 or less farrowings per year have high replacement rates due to increased sow culling as a result of open sows not fitting into the schedule and potentially larger gilt pools. These producers need to synchronize gilts as well as possible to reduce gilt pool size and strive for high farrowing rates. The most economical crossbreeding system for these producers is a rotaterminal including two maternal lines of boars mated in a rotation to produce replacement gilts and the terminal cross of terminal sires mated to the rotational cross females (Table 3). This system involves mating the best rotational cross sows to maternal line boars to produce additional replacement females. No replacement females need to be purchased. The use of artificial insemination with high indexing maternal sires will improve the economic returns of a rotaterminal crossbreeding system. The cost of producing replacement gilts in a rotaterminal crossbreeding system is the lower returns of the maternal litters. Also, the two breed rotational cross females have only 67% heterosis and thus are not as productive as F₁ or three breed cross females with 100% heterosis.

Table 3. System average, weighted by proportion matings in system.

Rotaterminal crossbreeding systems have two disadvantages. It is very important that the breed of sire for each gilt be identified. In a two breed rotation, if a purebred maternal breed of boar is mated to a female sired by the same breed, the resulting offspring have only 33% heterosis. The easiest way to avoid incorrect matings is to have a simple breed of sire identification mark such as an ear hole. If a sow loses its identification, the sow should only be bred to terminal cross boars for the remainder of her lifetime.

The third option is for a group of commercial producers to cooperatively operate a gilt multiplication herd utilizing either great grandparent or grandparent gilts. The commercial producer members could vary in size and purchase shares in proportion to replacement gilt needs. To operate efficiently, the herd should have at least 500 to 600 sows and operate a weekly farrowing system. Assuming 15% of total production in replacement gilt multiplication, a 600 sow multiplier should provide replacements for commercial herds totaling 3,400 sows.

To examine the economic benefits of a cooperative multiplier herd assume:

• a 25% replacement rate/litter farrowed, i.e., each gilt produces 4.0 litters in her lifetime.
• this allows a 640 sow multiplier herd to be established that produces 3168 selected F₁ gilts per year with a 50% selection rate (640 sows * 2.2 litters per year * 2.25 selected gilts per litter).

Cost Per Litter Produced

The cost per litter of $102.50 divided by 2.25 gilts per litter equals $45.55 per F₁ gilt produced not including transportation, vaccination, blood testing, and management costs. The overall cost will be approximately $55.00 above market price per gilt.

This system allows consistent selection. Gilts of the upper 44% are used in the multiplier herd and only F₁ gilts in the upper 50% are selected as replacements. Only highly superior Landrace boars, based on maternal line EPD index values, are used. The uniform genetic selection and supply of gilts benefits the commercial producer. The prices are very competitive especially in terms of the selection practices.

The formation of cooperative multiplier herds allows small to medium sized commercial producers to compete with much larger commercial producers who have established within-house grandparent and great grandparent gilt replacement programs. Because of the advantages to both seedstock and commercial producers, cooperative herds will likely be formed at an increasing rate until commercial producer demand for quality, competitively priced replacement gilts is met.

Cooperative multiplier herds can result in lower seedstock replacement costs. However, cooperative multiplier herds which have not been organized due to the difficulty of a group of independent commercial producers to make decisions. Continued increased competitiveness of the pork industry will encourage commercial producers to seriously consider and subsequently implement cooperative commercial herds.

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