Crossbreeding is a widely established management practice among commercial pork producers. Over the years, the industry has used rotational crossbreeding programs extensively. Rotational programs are relatively easy to operate, enable pork producers to develop their own females and exploit most of the possible heterosis.Reprint 6/95/5M

Bates, Ronald O.

University of Missouri: MOspace

Crossbreeding is a widely established manage-ment practice among commercial pork producers.Over the years, the industry has used rotational cross-breeding programs extensively. Rotational programsare relatively easy to operate, enable pork producersto develop their own females and exploit most of thepossible heterosis.Rotational programs do not use all the potentialheterosis and cannot effectively use breeds that areabove average for only one or two traits. Often breedsare included in a crossbreeding program because theyare superior for certain traits such as maternal,growth or carcass. Unfortunately, rotational programsoften do not maintain the desired breed composition.Table 1 demonstrates how pigs sired by boarsfrom Breed A are 57 percent Breed A, 28 percentBreed B and 14 percent Breed C. Pigs sired by Breed Bare 14 percent breed A, 57 percent Breed B and 28 per-cent Breed C. If Breed C is noted for growth and car-cass traits, only one-third of the pigs to be sold forslaughter will have 50 percent or more of that breedin its genetic composition. This also holds true for thesow herd. If Breeds A and B are noted for maternalcharacteristics, only two-thirds of the sow herd willmaintain more than 50 percent of either of these twobreeds in their genetic makeup.Terminal and rotaterminal systems described inthis publication can be adapted by producers toimprove the limitation of the more common rotation-al systems.Terminal programsTerminal programs are programs that concentrateon using all possible heterosis and capitalizing onbreed strengths. All effort is placed on maintaining100 percent heterosis in both the pigs and the sows,and selecting breeds and breed crosses that excel inmaternal or feedlot traits. Tables 2, 3 and 4 can beused to assess relative performance of differentbreeds and two-breed crosses. In general, superiorsow crosses are those that are 50 percent or more ofYorkshire, Landrace or Chester White breeding.Superior crosses for postweaning performance arethose that had a Duroc, Hampshire, Spotted,Berkshire or Poland China sire.Terminal programs are characterized by usingtwo-, three- or four-breed first cross females andshould not come from a rotational crossbreeding pro-gram. They can be purchased or produced on thefarm. Such specialized females are bred to boars thatare from breeds or breed crosses that are superior forgrowth and carcass traits. All the progeny from themating of these specialized females to terminal boarsare marketed. This is further illustrated in Figure 1.Terminal programs allow exploitation of all possi-ble heterosis and use specialized breeds or breed$.50 G 2311 Printed with soy ink on recycled paperMU GuideAGRICULTURALPUBLISHED BY UNIVERSITY EXTENSION, UNIVERSITY OF MISSOURI-COLUMBIASwine BreedingTerminal and Rotaterminal CrossbreedingSystems for Pork ProducersBy Ronald O. Bates, Department of Animal SciencesPercent of each breedBreed of sire A B CA 57 28 14B 14 57 28C 28 14 57Conception Litter size 21-day Age at Breed rate raised weight 220 lbs. BackfatBerkshire + - -Chester White + ++ - — ADuroc A A - + -Hampshire A - A - ++Landrace — ++ ++ A —Poland A +Spotted — — + -Yorkshire - ++ + + -Based on NC-103 review.Blank cell indicates data unavailable.A indicates performance near average of breeds studied.+ indicates performance superior to average.++ indicates performance substantially superior to average.- indicates performance inferior to average.— indicates performance substantially inferior to average.Archive version-- See xtensio.missouri.ducrosses. Unfortunately, developing replacementfemales becomes more complex. Replacement giltshave to be purchased or small nucleus herds must bemaintained to produce the first cross or Fl females. Iffemales are purchased, out-of-pocket costs increase aswell as health risks. If a small purebred herd is main-tained as a nucleus, the management programincreases in difficulty and cost of production for thepurebred herd may rise.However, if you’re buying replacement gilts froma seedstock supplier who follows a rigid herd healthprogram, you can routinely add purchased gilts to theherd with little health risk. To further secure healthstatus, develop a health agreement with the sellerbefore the transaction is final.The gilt procurement for a terminal program canbe handled in two ways. The first is that all replace-ment gilts can be purchased. All pigs produced willbe sold for market, and no replacements will be savedback. This often is referred to as the Mother Optionbecause all gilts purchased will be the mothers of allthe market hogs. The second way would be to pur-chase purebred or crossbred females. The purchasedgilts would make up a small portion (10 to 20 percent)of the sow herd and be mated to boars from maternalbreeds or lines different than the gilts. All replace-ment gilts for the rest of the sow herd would be cho-sen from the litters of the purchased females. This iscalled the Grandmother Option because the majorityof the market hogs would have purchased grand-mothers. Usually Fl gilts of maternal breeding arepurchased for the Grandmother Option.Rotaterminal programsRotaterminal programs are a compromise betweenrotation and terminal programs. Rotaterminal pro-grams are characterized by having a rotational pro-gram within a small portion (15 to 20 percent) of thesow herd to produce replacement females. The breedsused in the rotation program should excel in maternalcharacteristics.Page 2 G 2311Female breed crossesYorkshire- Chester White- Chester White-Trait Landrace Landrace YorkshireNumber born alive 9.2 9.8 10.1At 21 days 8.1b 8.4c 8.5cAt 65 days 7.8 8.1 8.0Litter birth wt., lbs. 32.1 34.3 32.3Wt., 21 days, lbs. 93.1 96.4 91.6Wt., 56 days, lbs. 260.3 272.4 255.2a Adapted from Kuhlers et al., 1988. JAS 66:1132.b, c Means in a row with different superscripts differ (P < 0.10).Table 3. Specific comparisons among Yorkshire, Landrace andChester White two-breed crosses for sow productivity.aFemale breed crossesYork- Duroc- Hampshire-Trait Landrace Landrace YorkshireNumber born alive 11.0 11.1 11.0At 21 days 8.9 9.1 9.2At 56 days 8.8 8.8 9.0Litter birth wt., lbs. 34.3 39.8 35.6Wt. at 21 days, lbs. 98.8 103.8 104.9Wt. at 56 days, lbs. 279.4 292.6 284.2a Adapted from Kuhlers et al., 1989. JAS 67:920.Table 4. Specific two-breed crosses among Yorkshire, Duroc,Landrace and Hampshire breeds for sow productivity.aFigure 1. Terminal crossbreeding program. A terminal crossbreeding program uses F1 females and terminal sire boars to producemarket hogs.Maternalbreed AMaternalbreed BF1 ABfemaleMarket all progenyTerminalsire boarThe majority (80 to 85 percent) of the sow herd ismated to boars of breeds or breed crosses that aresuperior in postweaning and carcass characteristics.More than 90 percent of the market offspring are siredby terminal boars and express 100 percent heterosisbecause their sire is of different breeding than that oftheir dams. Only a small portion of the market off-spring comes from the maternal rotation because allof the replacement gilts are taken from those matings.This is further illustrated in Figure 2.When implementing a rotaterminal program, onequestion often arises: “Should I use a two-, three- orfour-breed rotation to produce my replacementfemales?” Two-breed rotation females only express 67percent of the potential heterosis while four-breed rota-tion females express 93 percent of the potential hetero-sis (See Table 5).The real question becomes, “How much differencein maternal performance can we expect among thesedifferent rotational cross programs when all thebreeds in use are maternal in nature?” An examplecan be found in Table 6.When developing a rotaterminal program, thechoice of maternal breeds becomes critical. If allmaternal breeds under consideration are alike, thenthe choice could be to use a four-breed rotation to pro-duce replacement females, if it is practical. If thematernal breeds are not alike, as in Table 6, then thedecision becomes more difficult. Most pork producerswould choose the first two ranking breeds for a two-breed rotation, the top three breeds for a three-breedrotation, and so on. If the fourth ranking maternalbreed is inferior enough to the first three, the increasein heterosis used may not overcome breed differences.In Table 6, breed A was added to produce a four-breed rotation replacement female. The numberweaned did not increase over the three-breed rota-tion, and conception rate declined. In most situations,a four-breed rotation to produce replacement femaleswithin a rotaterminal program will not be beneficialbecause it is difficult to find four maternal breeds thatare similar in performance.G 2311 Page 3Figure 2. Rotaterminal crossbreeding program. A rotational crossbreeding program using maternal breeds is conducted on a small(15 to 20 percent) portion of the sow herd to produce replacement gilts. The majority (80 to 85 percent) of the sow herd is bred toterminal sire boars to produce market hogs.Maternal breed 1Maternal breed 2MaternalcrossfemaleTerminal boarMarket hogsTable 5. Heterosis of rotaterminal crossbreeding programs.Heterosis (%)Program Maternal ProgenyTwo-breed 67 100Three-breed 86 100Four-breed 93 100Purebred averagesTrait A B C DNumber born 9.2 10.8 11.6 10.5Number weaned 7.6 7.7 8.4 7.9Conception rate (%) 75.7 75.0 90.5 80.4Expected performanceNumber Number ConceptionProgram born weaned rate (%)Two-breed (B,C) 11.6 9.1 84.9Three-breed (B, C, D) 11.5 9.3 84.5Four-breed (A, B, C, D) 11.1 9.3 83.215-20 %80-85 %Sire selectionWhen using terminal or rotaterminal crossbreed-ing programs, sire selection is important. Purebredboars or gilts chosen to produce commercial femalesmust be from maternal breeds and from maternallines within breeds. These boars or gilts should befrom sows that rank in the top 25 percent of the herdfor a Sow Productivity Index that is used by the majorbreed associations or recommended by the NationalSwine Improvement Federation (NSIF). However,these boars and gilts also should be near average forgrowth and backfat when compared to the group inwhich they were tested to keep from decreasing thevalue of their market progeny. Terminal boars that areto be bred to specialized female crosses should be bet-ter-than-average for growth and backfat so theirprogeny excel for postweaning performance and arelean when slaughtered. No consideration should begiven to their merit for maternal traits.The use of crossbred boars often has been ques-tioned. Research has shown that crossbred boars aremore aggressive at a younger age and settle a largerpercentage of sows. Their progeny are no worse whencompared to pigs sired by purebred boars. Crossbredboars do work well as terminal sires in terminal androtaterminal programs. For instance, if Breed F isnoted for superior postweaning performance andBreed G is superior for leanness, Fl boars from cross-ing Breeds F and G would be more aggressive breed-ers, and their progeny should be better-than-averagefor both postweaning performance and leanness.When choosing crossbred boars, evaluating the par-ents is critical.Parents of potential crossbred herd sires shouldrank in the top half of the herd for the traits of inter-est. If they do not, then progeny sired by crossbredboars, from inferior parents, will only benefit fromhaving sires and dams of different breeding (100 per-cent heterosis), not from having above-averagegenetic merit.Page 4 G 2311 Reprint 6/95/5Mn Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United StatesDepartment of Agriculture. Ronald J. Turner, Director, Cooperative Extension, University of Missouri and Lincoln University, Columbia,MO 65211. n University Extension does not discriminate on the basis of race, color, national origin, sex, religion, age, disability or statusas a Vietnam era veteran in employment or programs. n If you have special needs as addressed by the Americans with Disabilities Actand need this publication in an alternative format, write ADA Officer, Extension and Agricultural Information, 1-98 Agriculture Building,Columbia, MO 65211, or call (314) 882-8237. Reasonable efforts will be made to accommodate your special needs.UniversityExtensionUNIVERSITY OF MISSOURICOLUMBIA

Terminal and rotaterminal crossbreeding systems for pork producers (1995)

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