Protein retention, growth performance and carcass traits of individually housed immunocastrated male- and female- and surgically castrated male Iberian pigs fed diets of increasing amino acid concentration

Immunocastration (IC, vaccination against gonadotropin releasing hormone (GnRH)) is one alternative to surgical castration (SC) for preventing sexual development and boar taint inmale pigs. A temporal increase in performance has been described for IC pigs before the second vaccination against GnRH. The objective of thisworkwas to assess the effects of IC on Iberian male and female pigs (fed diets of increasing CP content) on performance, nitrogen retention (NR) and digestibility, and carcass traits. Fifty-four pure Iberian pigs individually housed were allocated to a 3 x 3 factorial arrangement with three sex groups (IC males, IC females and SC males), three diets (153, 137 and 119 g CP/kg DM; 14MJ metabolisable energy/kg DM) and six pigs per treatment combination. Pigswere vaccinated at 18weeks of age (40 kg BW) and sevenweeks later (70-80 kgBW) and fed at 0.9 x ad libitumonBWbasis. Two digestibility and nitrogen balance assayswere performed before and after the second vaccination, respectively. Pigs were slaughtered at 105 kg BW. Before the second vaccination, Iberian IC males showed higher growth rate (g/day), feed efficiency, NR (g/day) and efficiency of NR than the other groups (P < 0.001). The NR and efficiency of NR was 40% greater in IC v. SCmales (P < 0.001). After the second vaccination, no differences in performance between sex groupswere detected (P> 0.05). Growth rate and feed efficiency were higher in IC males than in the other groups for thewhole experimental period (fromthe first vaccination to slaughter; P < 0.001). After the second vaccination, differences among sex groups in NR and the efficiency of NR disappeared (P> 0.05). NRefficiency was 0.177 on average. No significant effects of dietary CP were detected on performance. The NR was greater in pigs fed the 153 CP diet (17 to 37%; P > 0.05). Lean components of carcass (sirloin, loin and butt lean) were greater in IC males than in the other groups (0.001 < P < 0.05). There were no significant sex groupxdietary CP interactions. Iberian IC males grew at higher rate, deposited more protein, and more efficiently, than Iberian SC males before the second vaccination against GnRH. Iberian IC females showed similar growth performance to SC males and intermediate protein deposition efficiency between IC and SC males. Despite the higher growth performance, protein deposition rate, and efficiency of protein deposition of IC males v. SC males, no significant differences in amino acid requirements were detected between them. (C) 2021 The Authors. Published by Elsevier Inc. on behalf of The Animal Consortium.

Automated summary

The study showed that Iberian IC male pigs had significantly higher growth rate, feed efficiency, and nitrogen retention efficiency compared to other groups before the vaccination against GnRH. However, after the second vaccination, differences in performance between sex groups disappeared, with IC males still showing higher overall growth rate and feed efficiency.