DORAY, J. M., BURGES, J. C., CALLEJAS, S. S., SCHIERSMANN, G. C., TORCUATI, O., BUTLER, H. and ALBERIO, R. H. (1997) “Reproductive control in beef cows through vaginal progesterone; effects of various factors on fertility”, Archivos de Medicina Veterinaria, 29(1), pp. 63–68. doi: 10.4067/S0301-732X1997000100007.