In current breeding practices, management of the estrous cycle is common. Breeders want to know when their mare is in one phase or another and also want to be able to determine when she will ovulate. Manipulation of the estrous cycle is a breeding management practice. Estrus manipulation involves altering the normal cycle through hormonal treatments or other methods. Managing and manipulating the estrous cycle allows breeders to control what phase the mare goes through and how long she will stay in that phase. Estrus synchronization is the practice of regulating when one or more mares will be in estrus. Breeders can follow certain protocols to bring about synchronization in the cycle. According to Samper (2009), there are three methods to induce estrus. These are the induction of luteolysis, the prevention of estrus by progestins and progesterone with estradiol which allow natural luteolysis and are almost always associated with ovulation induction treatment. and follicular ablation. This article reviews and explores the hormones, methods, doses and protocols used to synchronize estrus in the mare. There are many reasons why breeders may want to synchronize the estrous cycle in a mare. When using chilled or frozen semen for artificial insemination, synchronization of the estrous cycle can significantly increase the efficiency of the breeding(s). There is a limited time in which the mare can become pregnant, by synchronizing her estrous cycle her chances of ovulating during this small window of time are greatly increased. Estrus synchronization allows breeders to coordinate the ovulations of several different mares to prepare them for the passage of embryos or oocytes...... middle of paper ......ryland Heights, MO: Mosby, Inc. French, AC, Thompson, AL, Davis, BG (2009) Discrete high-purity PEG oligomer crystals provide insight. Angew. Chemical. International Edition, Vol 48, Issue 7, page 1248. Retrieved 04/04/14 from http://users.ox.ac.uk/~dplb0149/publication/pub108.pdf.McKinnon, AO, Voss, JL (2005 ). Equine reproduction. Ames, IA: Blackwell Publishing Samper, J. C. (2000). Horse breeding management and artificial insemination. Philadelphia, PA: W. B. Saunders Company Samper, J. C. (2009). Equine breeding management and artificial insemination (2nd ed.). St. Louis, MO: Elsevier Health Sciences Squires, EL PhD (2008). Hormonal manipulation of the mare: a review. Journal of Equine Veterinary Science, Vol 28, No 11, pages 627-634. Retrieved 02/20/14 from http://wb.fvet.uba.ar/equinos/8313/review.PDF.fvet.uba.ar/equinos/8313/review.PDF