Inbreeding in Swine - PDF document

1 Inbreeding in Swine Fact Sheet Number 4 Purdue University Cooperative Extension Service West Lafayette, IN 47907 Author: David S. Buchanan, Inbreeding is the mating of individu-als that are related. In the strict sense, allmembers of a breed are related. As aresult, any seedstock producer ispracticing some inbreeding. Therefore,we generally reserve the term inbreed-ing for the mating of animals that aremore closely related than the average ofthe breed.Most breeds of livestock went througha phase of inbreeding early in theirdevelopment. This resulted from the 2 Step 2: List all paths that connect thesire and the dam.&#x----;&#x---D;&#x----;&#x---0;B Step 3: Locate the common ancestorin each path.&#x----;&#x---Ò; Ó--;&#x----;&#x-000;B The common ancestor is that indi-vidual that the arrows point away from.It is the ancestor that both parents traceback to.Step 4: Determine if the commonancestor in each path is inbred. If so,calculate the inbreeding coefficient ofthe common ancestors.The rules for determining the inbreed-ing coefficient of the common ancestorinbreeding coefficient of any otherRXYX1+Y BL value of path= | IÑ||| H| SÑ|||| II|| AÑ| S|| MZZÑ| A|| I D|| SÑ|||| A| DÑ||| I| AÑ|Common Ancestorn Value of Path�S ---- DF = .25*1_&#x----; ---;&#x-000;S F = 02_&#x----;&#xI---;&#x-000;&#x----;&#xI

---;&#x-000;S F = 03_ .0625 = .500 Inbreeding of S�path I---- A value = 1+1 (1+0) = .25




=relationship between =sum together all then =number of arrows =inbreeding coefficient =inbreeding coefficients 3 PathwaysCommon AncestornValue of PathZ F= .251Z F= .252&#x----;&#x-A--;&#x---0;Z F= 03Z &#x----;&#x-I-7;.90;----- S F= 04=1.125  .15.1125.1 ZSR = .8216





born birthlitter sizeweaning154-dayalive weightweaningweightweightnumber lbnumberlblb.10 -.3 -.07-.5-.97-2.3.20 -.6 -.10-1.1-2.79-10.9.30 -.9 -.11-1.8-5.10-22.2.40 -1.2 -.13-2.5-7.59-33.0.50 -1.5 -.18-3.1-9.91-39.2 4Uses of InbreedingInbreeding can have several benefitsto a seedstock producer if the breederunderstands how to monitor it and iswilling to sacrifice some performance inthe process. Inbreeding tends tosubdivide a breed into families that canbe identified and crossed with someunlikely to contribute to geneticimprovement but may aid in merchan-dising if other members of the familyhave done well. Certain families maydemonstrate superior performance, butif a family group has poor averageperformance, it should be discardedquickly.Inbreeding also promotes an increasein prepotency which is the ability of anindividual to consistently pass on itscharacteristics. This prepotency results

from the increase in homozygosity.Since an inbred individual will havemore homozygous gene pairs than apossible gene combinations for thesperm or egg cells. As a result theoffspring should be more similar toeach other.Figure 1. Pedigree of Roughneck |Gem ||Cara||Eric Linebreeding should be attemptedonly in superior herds that have diffi-culty finding outside boars that are ofsufficient merit to improve that herd.The ancestor that is the object of thelinebreeding should be clearly outstand-ing with reference to clear performancecriteria. A good linebreeding programtakes time to develop. During that timethe producer should be watchingindustry trends carefully. Not only is itimportant to know how to start alinebreeding program properly, it is alsoimportant to know when industry trendshave begun to emphasize new criteria sothat the linebreeding program focuseson the future instead of the past.RecommendationsInbreeding should be avoided as muchas possible by anyone that does not havea clear understanding of its use. Unlessof inbreeding far outweigh the advan-tool for perpetuating the genes from anoutstanding ancestor. It should be usedonly in herds that are superior and onlythose boars that are clearly outstandingshould be the object of a linebreedingprogram. Mating of close relatives, suchas brothers with sisters or parents withoffspring, should be avoi

ded in anysituation. Linebreeding is probably the bestknown use of inbreeding. It is an attemptto maintain a high relationship to someoutstanding ancestor while keepinginbreeding as low as possible. Thepedigree of Roughneck in Figure 1breeding. The degree of relationship toEric is high (.36) but inbreeding is at anacceptable low level (.06).Linebreeding has been attempted inmost breeds of swine. It has the advan-standing individuals that are no longeravailable for breeding purposes. It alsohelps in recognition since the breedercan use the name of the ancestor at thecenter of the linebreeding. This is fine ifthis ancestor is truly outstanding. Manyof the boars that are the object oflinebreeding are probably very good butthis may not be true in all cases. Otherdangers associated with linebreedinginclude the inevitable buildup ofinbreeding and the possibility oflinebreeding to an inferior son of anoutstanding boar.1/2000 (2M)It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director, that all persons shall have equal opportunity and access to itsprograms and facilities without regard to race, color, sex, religion, national origin, age, or disability. Purdue University is an Affirmative Action employer.This material may be available in alternative formats.1-888-EXT-INFOhttp://www.agcom.purdue.edu/AgCom/Pubs/menu.h