Thesis (PhD)--Stellenbosch University, 2018.ENGLISH ABSTRACT: In South Africa, Dohne Merino sheep are farmed extensively for wool and meat production. Ram lambs are typically castrated to enable easier management of mixed-sex flocks by manipulating reproduction and associated behaviour, while promoting fattening and improving meat quality. Due to various welfare concerns regarding the pain associated with castration and healing complications, the practice is under scrutiny, which necessitates producers to investigate alternatives to physical castration. International pork and beef industries have successfully applied immunocastration in commercial enterprises; however, no formal recommendations regarding its commercial application in the lamb industry are available. Improvac® was administered at two doses during the interval from weaning until slaughter and was sufficient in supressing testes growth and functioning in Dohne Merino ram lambs. Varying the interval between the two doses (two, three or four weeks) and the interval between second vaccination and slaughter (four or six weeks) did not influence growth performance or slaughter performance of ram lambs after weaning. The primary vaccine dose decreased serum testosterone concentrations, which resulted in a decrease in scrotal circumference, semen quality and seminiferous tubule size for all immunocastration vaccination schedules. Testes cut surface colour was redder and more yellow in immunocastrated than in intact rams, providing a possible on-line detection method for vaccination success after slaughter to ensure correct sex classification. An inter-vaccination period of two weeks and a six-week interval after second vaccination until slaughter, had the most pronounced and sustained effect on reproductive capacity of the rams, as well as the lowest frequency of injection site reactions. The recommended injection protocol for the commercial application of Improvac® in lambs involves subcutaneous administration on the flat surface of the shoulder area, and alternating shoulder sides per dose. Immunocastration resulted in improved welfare of ram lambs, when compared to rams castrated using the Burdizzo-method. The latter method resulted in increased serum cortisol concentrations, abnormal behaviours in response to pain experienced during the procedure, despite the use of pain mitigation, and tissue necrosis. Minor differences in offal yields were observed in immunocastrated lambs but no influence on carcass cutting yield or meat quality, other than cut surface colour, was reported. Thus, immunocastration can be considered a feasible alternative to physical castration in the commercial production of Dohne Merino ram lambs. However, further investigation is recommended into the application of immunocastration within a feedlot environment to further elucidate the effects on feed intake, nutrient requirements, differential fat deposition and behaviour in Dohne Merinos and other important meat-producing breeds in South Africa.AFRIKAANSE OPSOMMING: In Suid-Afrika word daar ekstensief met Dohne Merino skape geboer vir wol- en vleisproduksie. Ramlammers word tipies gekastreer om die bestuur van gemengde-geslags troppe te vergemaklik deur voortplanting en gepaardgaande gedrag te manipuleer, terwyl die bevordering van vetheid en vleiskwaliteit ook verbeter word. Weens verskeie welsynsbekommernisse, rakende die pyn wat verband hou met kastrasie en genesingskomplikasies, word die praktyk onder die loep geneem, wat produsente noodsaak om alternatiewe vir fisiese kastrasie te ondersoek. Internasionale vark- en bees industrieë het immunokastrasie al suksesvol in kommersiële ondernemings toegepas; daar is egter geen formele aanbevelings beskikbaar aangaande die kommersiële toepassing daarvan in die lamsbedryf nie. Twee doserings van Improvac® was toegedien tydens die interval van speen tot slag en was voldoende om testesgroei en -funksionering van Dohne Merino ramlammers te onderdruk. Wisseling van die interval tussen die twee dosisse (twee, drie of vier weke) en die interval tussen die tweede inenting en slagting (vier of ses weke), het nie die groeiprestasie of slagprestasie van ramlammers beïnvloed nadat dit gespeen is nie. Die primêre entstof dosis het serum testosteroonvlakke verminder, wat gelei het tot 'n afname in skrotale omtrek, semengehalte en seminifereuse buisie grootte vir alle immunokastrasie-inentingskedules. Die testis se gesnyde oppervlakkleur was rooier en meer geel vir die immunokastreerde ramme in vergelyking met die ongeskonde ramme, wat 'n moontlike vroeë deteksie metode bied om suksesvolle inenting na slagting te bepaal indien die inenting sukses bevraagteken word. 'n Inter-inentingsperiode van twee weke en 'n ses-week interval na die tweede inenting tot slag, het die grootste en mees volgehoue uitwerking op die voortplantingskapasiteit van die ramme, asook die laagste frekwensie van inspuitingsreaksies, gehad. Die aanbevole inspuiting protocol vir die kommersiële toediening van Improvac® vir lammers behels onderhuidse toediening op die plat oppervlak van die skouer area met die afwisseling van skouerkante per dosis. Immunokastrasie het gelei tot ‘n verbeterde welsyn van ramlammers in vergelyking met ramme wat met die Burdizzo-metode gekastreer is. Laasgenoemde metode het gelei tot verhoogde serum kortisolvlakke en abnormale gedrag in reaksie op pyn wat tydens die prosedure ervaar is, ten spyte van die gebruik van pynbeperking en weefselnekrose. Geringe verskille in afval opbrengste is waargeneem vir immunokastreerde lammers, maar geen invloed op karkas opsny opbrengs of vleiskwaliteit, behalwe gesnyde oppervlakkleur, is gerapporteer nie. Daarom kan immunokastrasie beskou word as 'n haalbare alternatief vir fisiese kastrasie tydens die kommersiële produksie van Dohne Merino ramlammers. Verdere ondersoek word egter aanbeveel vir die toepassing van immunokastrasie binne 'n voerkraalomgewing om die effekte op voerinname, voedingstof vereistes, differensiële vetdeposisie en die gedrag van Dohne Merinos en ander belangrike vleisproduserende skaaprasse in Suid-Afrika verder te verhelder
