MATERIALS AND METHODS
All the experimental procedures used in this study were approved by the Ethics Committee of the Universidad Politécnica de Madrid and were in compliance with the Spanish guidelines for the care and use of animals in research (Government of Spain, 2005).
Husbandry
Thirty-six pigs [(Landrace × Large White) sires × (Duroc × Large White) dams], weaned at approximately 23 ± 3 d of age and weighing 7.4 ± 1.2 kg, were obtained from a commercial farm. On arrival at the research station, the pigs were weighed, placed in individual flat-deck pens (1 × 1 m), and provided with an individual feeder and a nipple drinker. Room temperature was maintained at 31 ± 1°C for the first week of the trial, and then the temperature was reduced by approximately 2°C per week until reaching 26°C. The pigs had free access to water throughout the trial.