The Effects Of Primary Active Immunization Alone Against Gonadotrophin-releasing Hormone On Reproduction Traits, Performance And Carcass Characteristics Of Pigs

The aim of this study was to investigate the effects of an immunocastration vaccine, based on a GnRH tandem peptide construct, on reproduction traits, performance and carcass characteristics of pigs, and to explore the possibility of application of this immunocastration vaccine with single injection in practical pig farming in the future.In the experiment of immunocastration in male pigs, 36 crossbred boars (LargeWhite Rongchang) were randomly assigned to three groups of twelve animals each. The first group was intact boars and served as untreated controls. The second group was surgically castrated. The remaining group was immunized at 6 weeks of age with a GnRH-immunocastration vaccine. Pigs were fed ad libitum from 6 weeks of age onwards. All animals were slaughtered at 26 weeks of age. At slaughter, immunized boars with low testes weights, length and serum testosterone, were defined as responders. Immunized male pigs with testes weights, length and serum testosterone were similar to intact boars, were defined as non-responders. There were six responders and six non-responders, respectively.During the experimental period, testes length and serum testosterone levels of intact boars gradually increased, from 2.0cm and 1.41?.22ng/ml (6 weeks of age) tol0.38?.30cm and 11.17?.17ng/ml (26 weeks of age), respectively. At slaughter, testes length, testes weights and volumes of intact boars were 10.3 8?.30cm, 240.9?5.7g, and 155.02?4.57cm3, respectively. Serum testosterone levels of immunized boars were significantly lower (p<0.05) than of intact boars, from 4 to 16wpv (weeks post vaccination). At slaughter, serum testosterone levels (3.14?.84ng/ml) in responders were significantly lower (p<0.05) than in intact boars; serum testosterone levels in non-responders were3.0?.48ng/ml at 16wpv, which had reached 8.80?.28ng/ml and were similar to intact boars.at slaughter. Testes weights (151.0?9.6g), testes length (8.46?.45cm) and volumes (82.18 ?1.04cm3) of responders were significantly lower (p<0.05) than of intact boars; testes length (10.04?.18cm) in non-responders was similar to intact boars, but testes weights and volumes were between responders and intact boars at slaughter. Body weights of responders and surgically castrated boars were higher (p<0.05) than intact boars, body weights of non-responders were similar to intact boars at slaughter. During the experimental period, average daily gains of responders and surgically castrated boars were higher (p<0.05) than intact boars, average daily gains of non-responders were similar to intact boars; feed conversion ratio of intact boars were higher than surgical castrates and feed conversion ratio of immunocastrates were between surgical castrates and intact boars, but were closer to the intact boars. Dressing percentage of immunocastrates, surgical castrates and intact boars were similar; meat percentage of the immunized and intact boars were higher (p<0.05) than surgically castrated boars; fat percentage of the immunized and intact boars were lower (p<0.05) than surgically castrated boars at slaughter.In the experiment of immunocastration in female pigs, 36 crossbred female pigs (Large WhitexRongchang) were randomly assigned to three groups of twelve animals each. The first group was intact female pigs. The second group was surgically castrated female pigs. The remaining group was immunized at 6 weeks of age with a GnRH-immunocastration vaccine. Pigs were fed ad libitum from 6 weeks of age onwards. All animals were slaughtered at 26 weeks of age. At slaughter, immunized female pigs with reduced weights of ovary and uterus and no visible follicular structures or corpora lutea in the ovaries, were defined as responders. Immunized female pigs had similar weights of ovary and uterus to intact female pigs, and with follicular structures and corpora lutea in their ovaries, were defined as non-responders. There were seven responders and four non-responders, respectively.Intact female pigs had the first oestrus cycle at 10-11 weeks after the beginning of the exp...