Toniollo, Gilson Hélio, et al. “Progesterone -17alpha -OH and Androstenediona Serum Levels Evaluation During the Oestrus Cycle in Guilts (Sus Scrofa Domestica - Linnaeus, 1758)”. Brazilian Journal of Veterinary Research and Animal Science, vol. 35, no. 5, Jan. 1998, pp. 205-9, https://doi.org/10.1590/S1413-95961998000500002.