2.1. Animals

The experiment was conducted at a commercial swine farm (Agropecuaria Los Sagitarios S.A., Alajuela, Costa Rica) during 2019–2020 in the northwest of Costa Rica (Río Cuarto, 10°20′32″ N, 84°12′55″ W, Alajuela, Costa Rica, Central America) following the laws and regulations controlling experiments on live animals in Costa Rica. This study was performed following ethical principles, and with the approval of the Committee of Centro de Investigación y Desarrollo de la Agricultura Sostenible para el Trópico Húmedo at the Costa Rica Institute of Technology (CIDASTH-ITCR) according to Section 08/2020, article 1.0, DAGSC-100-2020. Eleven sexually mature and healthy boars from two commercial terminal male lines (ML: Duroc × Pietrain (n = 8) and Pietrain boars (n = 3)), 20.9 ± 3.0 (Pietrain) and 24.1 ± 9.8 (Duroc × Pietrain) months of age at the beginning of the experiment and of known fertility were used as semen donors in this study. For the study, the breeding boars were housed individually in well-ventilated pens with an average temperature of 25.6 ± 2.94 °C during the time of the experiment. The females came from four crossbred genetic lines (FL: York (Y), Landrace (L) and Pietrain (P), with the crossing schemes YLP-50 (¼ Y × ¼ L × ½ P), YLP-75 (¹/₈ Y × ¹/₈ L × ³/₄ P), YLP-87.5 (¹/₁₆ Y × ¹/₁₆ L × ⁷/₈ P), and Y-L-50 (½ Y × ½ L)). All of the females were bred on the farm and they came from maternal crossing schemes. Animals were fed with a standard breeder mixture (made on the farm) containing maize, soybean meal, mineral mixture, and common salt, as ingredients to fulfill the nutrient requirements according to the Nutrient Requirements of Swine [32]. Pregnant sows were provided with 2.5 kg of concentrated feedstuff in the first 2/3 of the gestation period and 3 kg in the final third. Males consumed 2.5 kg of concentrated feedstuff per day and were provided with water ad libitum. The gilts inseminated were 7 months of age, with a minimum weight of 145 kg.