Betteridge , K., B. Lillie, B. Quinn, R. Waelchli, J. Raeside, and M. Hayes. “Early Pregnancy in the Mare: Information to Interpret, Concepts to Accrue ”. Clinical Theriogenology, vol. 4, no. 4, Dec. 2012, p. 561, https://clinicaltheriogenology.net/index.php/CT/article/view/13618.