Steven H. Slusher, Equine Theriogenologist; Carolynn Taylor-MacAllister, Extension Veterinarian; David W. Freeman, Extension Equine Specialist, Oklahoma State University

Several management techniques are used for pregnancy determination. One of the simplest ways is to watch for signs of heat. A mare may be pregnant if she exhibits no signs of heat 18 to 20 days after her last ovulation. However, some mares may not cycle because of follicular or corpora luteal abnormalities, or they may have silent heat periods in which external signs of estrus are not evident. These problem mares would not be bred again if absence of heat was the only factor used to determine pregnancy. Because of these situations, other methods for pregnancy determination are commonly used.

Mares are most often rectally palpated 18 to 45 days following the last day of insemination. In recent years, real-time ultrasonography has gained attention for use in pregnancy determination. Ultrasonography can be used to obtain a visual image of the mare’s reproductive tract, and thus to detect pregnancy before palpation is normally performed. Ultrasonography is normally used following the 14th day post-breeding, but it can detect pregnancies as early as 10 days postovulation. As mentioned earlier, the ultrasound can also be used to detect estrus and follicular development, and it can be used with mares that have reproductive tract abnormalities or abnormal cycles.