1. Parry-Weeks, L.C. and D.W. Holtan, Effect of altrenogest on pregnancy maintenance in unsynchronized equine embryo recipients. J Reprod Fertil Suppl, 1987. 35: p. 433-8. 2. Daels, P.F., et al., Persistence of the luteal phase following ovulation during altrenogest treatment in mares. Theriogenology, 1996. 46(5): p. 799-811.