For Alternative Pork Chains: Breeding Programs

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Extension Bulletin E-3107 New August 2010SWINE BREEDING SYSTEMSfor Alternative Pork Chains:Breeding ProgramsRonald O. Bates State Swine Specialist Michigan State UniversityIntroductionThe pork industry has developed into multiple porkchains with particular specifications for targeted markets. These specifications can include final product attributes, scripted production practices or both. To meetthese varying specifications for differing pork chains,pork producers must match their production management and marketing practices to the requirements oftheir targeted market. This includes developing a breeding program that utilizes breed combinations that bestalign with the specifications of the pork chain(s) theytarget. This fact sheet will compare various crossbreeding systems, performance expectations of those systemsand methods of operation.CrossbreedingCrossbreeding is an important tool. If used correctly, itoffers pork producers an opportunity to genetically improve their production efficiency and, ultimately, lowerproduction costs. The use of crossbreeding is widespreadbecause offspring from matings between individualsfrom different breeds are typically hardier, grow fasterand perform better than purebreds. This improvementin performance of the crossbred individual over theaverage performance of its purebred parents is calledheterosis or hybrid vigor. It is thought that, during breedformation, portions of the gene pairs that control a traitbecame homozygous (two gene copies that are the same)for undesirable genes, which cause some suppression inperformance. Crossing animals from different breedsbreaks up these undesirable gene combinations. Differing genes within gene pairs in the crossbred individuallead to improved performance.Heterosis is expressed in both the growing and theadult pig. Crossbreds typically have a better survivalrate throughout their lives than purebreds and typicallygrow faster. This improved performance in the crossbredindividual is often referred to as individual heterosis.Crossbred dams are expected to have larger litters thantheir purebred counterparts with a higher survival ratethrough weaning, and wean heavier pigs. Heterosis indams that results in improved offspring performance isoften called maternal heterosis.The expected improvement in performance from heterosis is summarized for several traits in Table 1. Forexample, individual heterosis for number born alive is 1percent. This means that litter size for purebred damsTable 1. Heterosis advantage for production traits.PurebredItemPercentage advantage overFirst crosspurebred sowMultiple crosscrossbred sowReproductionConception rate0.08.0Pigs born alive1.08.0Litter size at 21 days9.023.0Litter size weaned10.024.021-daylitter weight10.027.0ProductionDays to market6.56.5Feed/gain2.02.0Carcass CompositionBackfat thickness-2.0Loin muscle area1.0Marbling0.3Extension-2.02.01.0

Swine Breeding Programs for Alternative Pork Chains: Breeding ProgramsFigure 2. Yorkshire by Landrace sow expectations.farrowing a crossbred litter should be 1 percent largerthan for dams of the same breed farrowing purebredlitters. For a two-breed-cross sow farrowing a litter thatis a three-breed cross, the expected improvement is 8percent. This demonstrates how strategically developing crossbred sows can easily and repeatedly improvematernal performance. This is further demonstrated inFigure 1 with an example of Yorkshire and Landracedams. The purebred average for Yorkshire is 11.1 pigsborn alive. If a purebred Yorkshire farrows a crossbredlitter, the expected average number born alive is 11.2.For Yorkshire-Landrace F1 females bred to a boar ofa third breed, however, the expected average numberborn alive is 11.6, even though the Yorkshire-Landraceaverage is 10.9. The 0.7 increase in pigs per litter abovethe purebred average is due to heterosis that occurswhen a crossbred litter is farrowed by a crossbred dam.11.611.41110.811.410.810.2Y-L F1Yx(Y-L F1)Rotational systems. Rotational systems have beenpopular in the pork industry. They are easy to understand and require the purchase of only boars or semen.Replacement females are produced internally fromeach of the boar breeds used in the rotation. Rotationalsystems do not allow for optimal exploitation of heterosis, however. Table 2 shows the expectation of heterosislevels through each advancing generation of a rotationalcrossbreeding system. In the first one to three generations of the rotation, depending on the number ofbreeds involved, pigs do exhibit 100 percent heterosis,but as the generations advance, heterosis levels, bothindividual and maternal, decline to an equilibrium level.Heterosis within the two-breed rotation declines to67 percent compared with the initial cross; the fourbreed rotation stabilizes near 93 percent. A three-breedrotation is expected to maintain 86 percent of possibleheterosis (Table 3).11.510.910.7510.4Y-L avgYorkshire (Y) Landrace (L)Various schemes for crossing breeds can assist producers in developing a breeding program that best fits theirmanagement program and target markets. The followingcrossbreeding systems should be investigated for use invarious pork production and marketing chains. Performance expectations using example breeds have beencalculated for each breeding system for comparisonpurposes.11.1Yorkshire (Y) Landrace (L)10.75Breeding Systems10.610.211.110.411.21111.410.6Figure 1. Comparison of F1 and purebred sowperformance for the Yorkshire and Landrace breeds.Born Alive11.511.2Crossing animals that have breed ancestry in common,often referred to as backcrossing, allows for reformation of some of the original undesirable gene pairs. Thisreduces heterosis. For example, in Figure 2 are theexpectations for average number born alive for Yorkshireand Landrace purebred females, for Yorkshire-LandraceF1 females and for backcross females produced by mating a Yorkshire boar to Yorkshire-Landrace F1 females.The performance expectation for backcross females islower because of declines in heterosis.11.6Born AliveY-L F12

Swine Breeding Programs for Alternative Pork Chains: Breeding ProgramsTable 2. Heterosis in rotational crosses.Generation numberCrossbreeding system123456EquilibriumTwo-breed rotation100.050.075.062.568.967.266.7Three-breed Rotation100.0100.075.087.587.584.485.7Four-breed rotation100.0100.0100.087.593.893.893.3Rotational systems may be simple in concept but can bedifficult to implement correctly. Sow herds in rotationprograms will be sired by every breed of boar in therotation, but producers using rotational programs typically maintain only one breed of boar on the farm at atime. This dictates that producers will breed a percentage of the sows to a boar of the same breed as their sire.This causes a reduction in heterosis and consequently areduction in performance and vigor.semination, it is a relatively easy process to order semenfrom each breed of boar needed. Correct operation of atwo-breed and three-breed rotation program is illustratedin Figure 3.Terminal systems. Conceptually, terminal breedingprograms exploit all possible heterosis within each crossand capitalize on breed strengths. Heterosis is typicallymaintained at 100 percent in both the pigs and the sows.Breeds are selected and used in a systematic fashionto utilize their strengths within the cross. Typically,breeds such as Yorkshire, Landrace or Chester White,which excel for sow productivity, are used to producetwo-breed or three-breed specialized maternal-crossfemales. Boars from breeds that are noted for postweaning performance, carcass merit or meat quality, such asDuroc, Hampshire and Berkshire, are mated to theseTo operate a rotational system correctly, producers mustmaintain on the farm boars from each breed within therotation. Simple programs can be developed to identifythe breed of boar that sired each sow so that the sow willbe mated to the correct breed of boar. Using a comprehensive artificial insemination program simplifies this. Ifmost or all of the matings are completed by artificial in-Table 3. Performance expectations for different crossbreeding 51111.57.67.98.28.5Postweaningavg. dailygain 80.90.9Crossbreeding systemRotationalsystem with breeds B, C, D11.59.41.900.93Terminalsystem with CxD females and B as a terminal sire11.99.81.940.90Rota-terminal system with a C by D maternal11.79.31.94rotation and B as a terminal sire30.90

Swine Breeding Programs for Alternative Pork Chains: Breeding ProgramsFigure 3. Two- and three-breed rotational programs.Breed AXBreed ABreed BFemale offspringfrom each sirebreed are usedas replacements.Female offspringfrom each sirebreed are usedas replacements.Breed BIn a two-breed rotation, females sired byBreed A are mated to boars from Breed B.Females sired by Breed B are matedto boars from Breed A.Breed CIn a three-breed rotation, females sired by Breed A are matedto boars from Breed B. Females sired by Breed B are bred toto boars from Breed C. Females sired by Breed C are matedto boars from Breed A.Figure 4. Terminal breeding system.maternal cross females to produce market pigs. Figure4 illustrates a terminal cross program. In this example,all females used on the farm would be purchased as wellas the boars or semen used to produce the market pigs.Performance expectations (Table 3) have been calculated for a terminal system that utilizes a two-breed F1female for the sows and mates sows to a terminal breedthat is superior for postweaning performance to producemarket pigs.PurchasedCrossbred giltXThis program does have increased annual variable orout-of-pocket costs but typically yields the highest profit.In an effort to reduce regular cash expenditures, a variation of this program – grandparent terminal system – isshown in Figure 5. A small percentage (10 to 20 percent) of the sow herd consists of purchased females usedto produce replacement gilts. These internally producedgilts make up the bulk (80 to 90 percent) of the sowherd. These internally produced females are mated toterminal boars to produce market pigs. This system haslower out-of-pocket costs and just slightly lower profitability expectations than the terminal program.Market PigsTerminal boar(Duroc, DxH, etc)Rota-terminal systems. Rota-terminal breeding systems are somewhat of a blend of rotational and terminalsystems. Rota-terminal systems use a rotation within asmall portion of the herd (10 to 20 percent) to generatereplacement females. Breeds used to produce replace-4

Swine Breeding Programs for Alternative Pork Chains: Breeding ProgramsFigure 5. Grandparent terminal system.Breed BXA common question about rota-terminal programs iswhether it is better to have two or three breeds withinthe maternal rotation. In a two-breed maternal rotation, maternal heterosis retention is 67 percent; in athree-breed rotation, maternal heterosis retention is 86percent. Higher heterosis levels imply improved maternal performance. If a three-breed maternal rotation isconsidered, the next question is: what third breed or lineshould be included within the maternal rotation?This question is a good one and may be best answeredwith an example. In Table 4 are performance levels offour example breeds or lines (A, B, C, D). The table alsocontains the expectations for three maternal rotationsusing various combinations of the four breeds.Breed APurchased femaleParent giltproducedinternallyF1XMarket PigsEvaluating the calculated performance for these rotations shows that the two-breed rotation using breeds Cand D is best for litter size born and conception rate.One of the two three-breed rotations, (B, C, D) is betterfor number weaned, even though breed B has poorerperformance for number weaned. Heterosis has a largeimpact on number weaned. More heterosis is retainedTerminal boar(Duroc, DxH, etc)ment females should excel in maternal characteristics.For each mating group (e.g., weekly, biweekly, monthly,etc.), 10 to 20 percent of the sows are mated to maternal boars from a differentFigure 6. Rotaterminal breeding system.breed than the sow’s sireto produce replacementfemales. At birth, gilts fromBreed Athese maternal matingsmust be identified so that,at the completion of thefinishing phase, prospective replacement gilts can%be easily selected andBxA-1501removed from finishing,acclimatized and inteParentgrated into the breedingReplacementsherd. Within a breedinggroup, sows not mated forAxBreplacement gilt produc85-90%tion are bred to terminalboars or with semen froma breed that excels inpostweaning performance,Breed Bcarcass merit and/or meatTerminalquality. This is further il(Duroc, Hamp, etc.)lustrated in Figure 6.X5Market Pigs

Swine Breeding Programs for Alternative Pork Chains: Breeding ProgramsTable 4. Performance Expectations for MaternalRotations in a Rota-terminal System.the implementation of the breeding system. Utilizing athird maternal breed may provide an improved potentialfor maternal performance if farm management is capable of successfully implementing this system. Management and breeding personnel must be able to correctlyidentify the breed of sire of gilt replacement candidates.This can be achieved by simple identification systemssuch as ear notching or tags. In addition, managementand breeding personnel must be able to breed designated females with the correct semen or boars. Breedingfemales with the wrong semen or boar can cause furtherreductions in heterosis in resulting replacement females(e.g., breed a Yorkshire-sired female to a Yorkshireboar) and reduce maternal performance potential. Athree-breed maternal rotation in a rota-terminal breeding program can improve the potential for maternalperformance. The potential improvement may be onlymarginal, however, and if the system is not operated correctly, the actual performance could be poorer than thatof a two-breed maternal rotation.PurebredaveragesTraitNumber bornNumber weanedConception Rate, %Maternal rotationTwo-breed (C, D)Three-breed (B, C, D)Three-breed (A, C, D)ABCD107.67010.57.975118.28011.58.585Maternal rotationexpectationsNumber Number Conceptionbornweanedrate, %11.711.511.49.39.49.383.582.180.6in the three-breed rotational cross than in the two-breedrotational cross, so number weaned is slightly higher inthe three-breed rotational cross.ConclusionThere is a great deal to learn from inspecting the performance of these example breeds. In this example, breedsC and D would be considered maternal breeds becausethey have the highest expectation for number born andweaned. Number born and weaned is lower for breed Bthan for breeds C and D. Breed A is inferior to the otherthree breeds for these sow productivity traits. This example shows that improvement in maternal performancedue to heterosis can overcome the somewhat poorerperformance of the third breed, breed B, even compared with a two-breed rotation of two superior maternal breeds such as breeds C and D. Increased heterosisin a three-breed rotation can not overcome inclusion ofan inferior maternal third breed, however, such as breedA, when the three-breed rotation is compared with atwo-breed rotation of superior maternal breeds such asbreeds C and D.When developing a breeding system, producers mustdecide what type of system best fits their managementcapabilities, production facilities and target market. Aterminal crossbreeding system in which all females arepurchased from an outside source may be the best system. Whether it is depends on the genetic backgroundof the gilts, their health status and the target marketfor the producer. Most producers develop replacementfemales within their farm systems to protect their healthstatus, and to produce replacement gilts with a geneticcombination that best fits their production facilities andthe ability to produce progeny that meet the specifications of their target markets.ExtensionMSU is an affirmative-action, equal-opportunity employer. Michigan State UniversityExtension programs and materials are open to all without regard to race, color,national origin, gender, gender identity, religion, age, height, weight, disability,political beliefs, sexual orientation, marital status, family status or veteran status.Issued in furtherance of MSU Extension work, acts of May 8 and June 30, 1914, incooperation with the U.S. Department of Agriculture. Thomas G. Coon, Director,MSU Extension, East Lansing, MI 48824. This information is for educationalpurposes only. Reference to commercial products or trade names does not implyendorsement by MSU Extension or bias against those not mentioned.Several important points must be considered when aproducer is implementing a rota-terminal breedingscheme to produce replacement females. The first decision must be how many (two or three) breeds or lineswill be used in the maternal rotation. The next matter isNew 8/10 – 500 – LKP/SP6

Swine Breeding Programs for Alternative Pork Chains: Breeding Programs 2 farrowing a crossbred litter should be 1 percent larger than for dams of the same breed farrowing purebred litters. For a two-breed-cross sow farrowing a litter that is a three-breed cross, the expected improvement is 8 percent. This demonstrates how strategically develop-

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