Morbidity and mortality of mare and foal following dystocia - a literature review

Dystocia represents a life-threatening condition for mare and foal. Morbidity and mortality rates due to a difficult birth, as well as the influence on fertility of the mare were analyzed, based on a review of publications. This was aggravated by the fact that no standardized diagnostic code was used and that most publications do not clearly describe how extensively the examinations were performed beforehand. Retentio secundinarum is the most common complication caused by dystocia. Other complications are injuries to the soft birth canal and the colon. These occur more frequently after surgical obstetrics than following assisted vaginal deliveries. Performing a fetotomy increases the risk of injury to the birth canal. After a caesarean section, the risk for retained placenta increases significantly. In order to evaluate the possibility of medical progress over time, mortality rates of mare and foal were investigated and divided in surgical and conservative obstetrics within the period of 1970-1990 and 1991-2021. The average maternal mortality rate following caesarean section amounted to 18% in the time period between 1970 and 1990 and 14% between the years from 1991-2021. After fetotomy, the two determined mortality rates amounted to 29% and 10% for the time between 1970 and 1990. In the period 1991-2021, the rate varies between 4% and 44% with an average mortality rate of 14%. Following controlled vaginal delivery, the average mortality rate is 9%. Literary sources were however only available for the current time period and range between 6% and 29%. The morbidity and mortality rate of foals is very high. Following caesarean section on average 53% of foals are dead on delivery, with a range of 13-79% in case reports from the years 1991-2021. The number of dead foals in the context of conservative obstetrics is of a similar scale. Postnatal foal diseases are largely due to intrapartum hypoxia during dystocia and obstetric injury. In consequence of a difficult delivery, mares experience reduced fertility. In numerous cases this however may be compensated by pausing from further breeding in the same year. The number of cases evaluated in this context however remains too small to advocate any recommendations for breeding following incidents of dystocia.