Immunocastration and its application in ram lambs

[摘要] 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.

[发布机构] Stellenbosch University