The objective of this study was to evaluate the incidence of pregnancy loss, considering the periods of occurrence, reproductive status, as well as the different age groups. During the breeding seasons of 1998/1999 and 1999/2000 (September to January) the gestations of 445 Quarter Horse mares with ages from 3 to 20 years were monitored, comprehending maiden, barren and lactating. Pregnancy diagnostic was performed by ultrasonography at the 11th day after ovulation and repeated on days 20, 30, 40 and 50. The mares were distributed in groups from I to IV, corresponding to pregnancy losses between days 11 to 20, 21 to 30, 31 to 40 and 41 to 50, respectively. The overall pregnancy loss rate was 8.53% (38/445), being of 5.39% (24/445); 1.57% (7/445); 1.12% (5/445) and 0.45% (2/445) for groups I, II, III and IV, respectively. The unique and significant incidence (P<0.05) occurred in group I (63.15%, 24/38), showing that the time between the second and third weeks is the most susceptible to pregnancy loss. The loss rates were not significantly different (P>0.05) concerning reproductive status and age groups.
pregnancy loss; embryonic death; equine; mare
