Ractopamine under dietary protein adjustment improves growth performance and carcass traits of immunocastrated and surgically castrated pigs slaughtered 21 days after vaccination

Abstract

The objective of this study was to evaluate the effects of immunocastration and ractopamine hydrochloride (RAC) supplementation on growth performance and carcass traits of male pigs slaughtered 21 days after the second immunization. Sixty-four pigs (Landrace × Large White, initial body weight 103.05 ± 0.67 kg) were individually tagged and randomly assigned to a 2 × 2 factorial arrangement in a completely randomized design, consisting of two castration methods (immunocastrated vs. surgically castrated) and two dietary RAC levels (0 or 10 ppm). No castration method × RAC interactions were observed for any variable ( P > 0.05). Immunocastrated (IM) pigs exhibited 19.5% greater average daily gain (ADG) and 13% lower feed-to-gain ratio (FG) compared with surgically castrated (SC) pigs ( P < 0.05). IM pigs also showed reduced backfat thickness across all measurement sites and greater lean meat percentage, whereas SC pigs had higher carcass yield ( P < 0.05). Ractopamine supplementation under increased amino acid supply increased ADG by 13.6%, improved hot carcass weight by 3.1%, and reduced FG by 13% ( P < 0.05). Overall, immunocastration improved growth performance and carcass leanness, while RAC supplementation increased average daily gain by 13.6%, confirming its additive effect under a shortened 21-day post-immunization interval. Immunization against GnRH combined with RAC feeding represents an effective strategy for producing heavy-weight finishing pigs with improved efficiency.

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