Cloete, Schalk W. P.Van Wyk, Japie B.Van der Linde, Theuns C.Scholtz, Anna Jacoba2015-11-062015-11-062010-052010-052010-05http://hdl.handle.net/11660/1525English: The study includes separate papers, which are all linked by their emphasis on the control of blowfly strike, and breech strike in particular. This summary is intended to provide readers with a broad overview of the outcomes of the study. Part I. Management options Chapter 3 dealt with a survey on the prevalence of blowfly strike, and the methods used to combat blowfly strike, in the Rûens area of South Africa. It was clear from the survey that breech strike is the major form of strike in the Western Cape. Mulesing was once again demonstrated to be an effective control method for breech strike. With the termination of mulesing as an acceptable management practice, this chapter highlights the need for alternative methods to be used for blowfly control. Although useful from an IPM perspective, other initiatives that could add to blowfly control failed to have the same marked impact on blowfly strike that mulesing had. Chapter 4 reports on the effect of regular treatment with crystals derived from Aloe spp for potential use as a natural anthelmintic in yearling Merino progeny. The short-term effect of aloe treatment was also considered. Results showed no reduction in the parasite burden when sheep were treated with Aloe. The contribution of this treatment to blowfly IPM is thus limited. Part II. Breeding options Divergent selection for reproduction (defined as the ability of ewes to rear multiple offspring) resulted in lines that differed markedly for their susceptibility to breech strike as a correlated effect (Chapter 5). The line selected for reproduction (High line or H line) was substantially more resistant to breech strike than the line selected for low reproduction (Low line or L line). Chapter 6 reported genetic (co)variances between wrinkle scores and the absence of breech strike in mulesed and unmulesed Merinos. This chapter suggested that breech strike on the underlying scale is partly under genetic control. Indirect selection levelled against skin wrinkle could play a role in reducing the susceptibility of sheep to breech strike in unmulesed sheep only. The significant genetic variation for absence of breech strike remaining in mulesed sheep hints at traits not associated with wrinkles and bare breeches (which are arguably being strived for during the Mules operation) also being important in breech strike resistance genetics. In Chapter 7 subjective scores for dags, breech cover, crutch cover and belly quality were recorded for mature and maiden ewes in the divergently selected lines in an attempt to understand the reasons for the lower susceptibility to breech strike in the H line. Animals in this line displayed desirable breech and crutch characteristics compared to contemporaries selected against reproduction (L line). This generalisation held true for mature reproducing ewes as well as for two-tooth hoggets. Dag scores were accordingly improved in hoggets in the H line. In a further study (Chapter 8) it was shown that autumn and spring dag scores; breech wrinkle score as well as the vertical and horizontal breech bare areas were all heritable in the lines divergently selected for reproduction. Genetic correlations among the breech traits were generally favourable. Yearling live weight was favourably related to breech traits on the genetic level. The only genetic correlation of breech traits with fleece traits that would cause concern was a positive correlation between clean fleece weight and breech wrinkle score. Derived breeding values in this chapter confirmed substantial genetic differences for both dag scores, breech wrinkle score and breech bare area in favour of the H line. Results from Chapter 9 indicated that H line hoggets took substantially shorter time to be crutched than their L line contemporaries, indicating welfare benefits in favour of the former line. Implications The study has shown definite opportunities for the alleviation of breech strike and presents the scientific community with ample opportunities to refine and integrate existing control measures in a comprehensive IPM strategy. However, further research is needed to reach this objective.Afrikaans: Die proefskrif bestaan uit aparte artikels, wat almal onderling met mekaar verband hou en wat die belangrikheid van die beheer van brommeraanvalle, en meer spesifiek broekaanvalle, beklemtoon. „n Opsomming van die artikels het dus ten doel om aan die leser „n breë perspektief oor die uitkomste van die studie te voorsien. Deel I. Bestuursopsies Hoofstuk 3 handel oor „n opname na die voorkoms van en die metodes wat gebruik word om brommeraanvalle te beheer in die Rûens gebied van Suid-Afrika. Dit was duidelik uit die ondersoek dat broekaanvalle die belangrikste vorm van brommeraanvalle is. Ironies genoeg is dit weereens bewys dat die Mules operasie „n baie effektiewe metode vir die beheer van aanvalle in die broek is. Met die uitfassering van die Mules operasie as „n aanvaarbare bestuursmaatreël, beklemtoon hierdie hoofstuk die nodigheid van alternatiewe brommerbeheermaatreëls. Gesien in die lig van bruikbaarheid in „n Geïntegreerde Plaagbeheer Bestuursprogram (GPB), het geen van die ander beheermetodes wat aangewend word dieselfde merkbare impak gehad as die Mules operasie nie. Hoofstuk 4 verskaf inligting oor die effek van die gereelde gebruik van Aalwyn kristalle as „n natuurlike interne parasiet wurmmiddel in jaaroud Merinos. Die korttermyn effek van Aalwyn behandeling is ook ondersoek. Geen verlaging in die parasietlading kon waargeneem word nie. Die bydrae van hierdie behandeling tot „n GPB vir brommers is dus beperk. Deel II. Telings opsies Seleksie vir reproduksie (gedefinieer as die vermoë van ooie om meerlinge groot te maak) het tot gevolg gehad dat lyne wat uiteenlopend geselekteer is vir reproduksie beduidend van mekaar verskil het ten opsigte van hulle ontvanklikheid vir brommeraanvalle, as „n gekorreleerde effek (Hoofstuk 5). Die lyn geselekteer vir reproduksie (Hoë lyn of H lyn) was beduidend meer weerstandbiedend teen broekaanvalle as die lyn geselekteer teen reproduksie (Lae lyn of L Lyn). Hoofstuk 6 verskaf inligting oor genetiese (ko)variansies tussen punte vir broekplooie en die afwesigheid van broekaanvalle in skape wat ge‟mules” en nie ge‟mules‟ is nie. Hierdie hoofstuk dui aan dat broekaanvalle op die onderliggende skaal gedeeltelik onder genetiese beheer is. Indirekte seleksie gemik teen broekplooitellings om die vatbaarheid van skape vir broekaanvalle te verminder, kan alleenlik „n rol speel by skape wat nie ge‟mules‟ is nie. Die beduidende genetiese variasie vir die afwesigheid van broekaanvalle wat oorbly in skape wat ge‟mules‟ is, dui daarop dat ander eienskappe wat nie verwant is aan plooie en oop areas in die broek nie (waarna gestreef word met die Mules operasie), ook belangrik is in die genetika oor vatbaarheid vir broekaanvalle. In Hoofstuk 7 is subjektiewe punting vir misklosse; wolbedekking in die broek- en mik areas; sowel as kwaliteit van wol op die pens aangeteken vir volwasse en onvolwasse ooie in die lyne wat geselekteer is vir uiteenlopende reproduksie. Die doel van die studie was om die redes vir laer vatbaarheid in broekaanvalle in die H lyn vas te stel. Diere in laasgenoemde lyn het gunstige broek- en mikeienskappe gehad in vergelyking met diere in die lyn wat geselekteer is teen reproduksie (L lyn). Hierdie veralgemening het gegeld vir volwasse ooie sowel as tweetand ooie. Misklos punte is dienooreenkomstig verbeter in tweetand ooitjies in die H lyn. In „n verdere studie (Hoofstuk 8) op die seleksielyne wat uiteenlopend vir reproduksie geselekteer is, word aangetoon dat subjektiewe punting van broekplooie en misklosse in die herfs en lente; sowel as die vertikale en horisontale metings van die wolvrye broekarea oorerflik is. Genetiese korrelasies tussen hierdie broekeienskappe was in die algemeen gunstig. Liggaamsgewig op jaaroud ouderdom is op genetiese vlak gunstig verwant aan die broekeienskappe. Die enigste genetiese korrelasie tussen broekeienskappe en vageienskappe wat rede tot kommer veroorsaak, is die positiewe korrelasie tussen skoonvaggewig en broekplooi punting. Beraamde teelwaardes bevestig merkbare genetiese verskille ten gunste van die H lyn vir beide misklos- en broekplooi punte; sowel as vir oop areas in die broek. Resultate uit Hoofstuk 9 dui daarop dat dit korter neem om tweetand skape in die H lyn te mikskeer as in die L lyn, wat voordele vir die H lyn, in terme van welsyn, inhou. Implikasies Hierdie studie dui op definitiewe geleenthede om broekaanvalle te verminder en verskaf die wetenskaplike gemeenskap met verskeie opsies om bestaande beheermaatreëls te verfyn en te integreer in „n omvattende GPB strategie. Verder navorsing is egter nodig om hierdie doel te kan bereik.enBlowfly strikeControl methodsBlowflies -- Control -- South AfricaLucilia cuprinaSheep -- Diseases -- PreventionPests -- Integrated controlThesis (Ph.D. (Centre for Sustainable Agriculture and Rural Development))--University of the Free State, 2010ThesisUniversity of the Free State