2.2. Animals

Data were collected from 60, 5-day old male piglets (Yorkshire x Landrace) obtained from twelve different litters delivered by third-parity sows. Neonates with abnormalities in the position of the testicles (unilateral or bilateral cryptorchidism, scrotal hernias, etc.) or signs of systemic disease were excluded. Following the regular handling practices at the host farm, on day 3 post-farrowing, all piglets received a subcutaneous injection of 1 mL (100 mg) of Fe³⁺ in the form of iron dextran. They were not subjected to tooth or tail resection before the experiment. The sows and their litters were held in 1.9–2.5 m² farrowing pens. Dimensions were 2.07 m long × 0.60 m wide × 1.01 m high, with a total space of 2 m wide by 2.5 m long. Each pen was equipped with a 50-cm stainless steel feeder and a nipple drinker, and its creep area was warmed by a radiant electric lamp. Each room had 12 pens set up in two rows of six pens each with a dividing aisle. The pens had slatted, wire mesh floors with a plastic carpet over them. Fans and air-heating were installed to control ventilation and temperature (27 °C and 60% relative humidity in the farrowing room). Sows and piglets had ad libitum access to water in separate nipple drinkers. On day one of life, all piglets were weighed and identified individually by marking a number on their back in different colors to distinguish the experimental groups. All procedures were carried out by the same person and near the farrowing pens.

Each one of the five study groups consisted of 12 piglets divided according to the number of incisions (one or two) received during surgical castration and with or without the use of the local anesthetic, lidocaine. There was also a control group that underwent simulated castration (SIM). The groups were identified as follows: castration with one horizontal incision in both testicles with and without lidocaine as a local analgesic (C1+L and C1); castration with two vertical scrotal incisions with and without local anesthesia (C2+L and C2); and a control group with piglets that were removed from their pens and held head-down by their hind limbs for approximately 90 s (SIM) near the farrowing pen similar to the groups subjected to surgery.