Material and methods
The experimental design included 120 pigs. Two were removed from the study: one pig was a cryptorchid male, and the other grew poorly. The final evaluation included 118 (Landrace × Duroc) × Pietrain crossbreed pigs: 23 males surgically castrated under 7 days of age (CM), 24 females (FE), 35 entire males (EM) and 36 males (IM) vaccinated against boar taint using Improvac® (200 μg of GnRH–protein conjugate per ml of an aqueous adjuvant system) administered twice, when the pigs were aged 77 ± 3 and 146 ± 3 days. The pigs were reared at the experimental station of IRTA Monells, Spain. Each pen measured 3.7 × 3.6 m with a floor surface that was 60% solid concrete and 40% slatted, and had one drinking bowl, a feeding station comprising a single-space food hopper and a trough with electronic identification system. Each pen contained 12 pigs and only pigs from the same treatment group were penned together. At an average age of 180 days, pigs were slaughtered at IRTA’s Monells slaughterhouse located 300 m from the experimental station. Pigs were slaughtered in five batches of 23–24 animals, with all experimental groups represented in equal proportions within each slaughter batch (Table 1). All batches were slaughtered within 2 weeks, starting with the heaviest pigs based on weights measured prior to transportation to the slaughterhouse. Pigs were fasted before transport to the slaughterhouse, and the different treatment groups were not mixed during transportation. After arrival at the slaughterhouse, pigs were penned by treatment group, and slaughtered 1–3 h later using standard ante-mortem procedures to minimise stress. Pigs were stunned using 85% CO2.