What is the primary clinical sign of a "red bag" delivery in mares?

The primary clinical sign of a "red bag" delivery in mares is the premature separation of the placenta from the uterine wall, which is referred to as placental abruption. In this case, the chorioallantois or the outer membrane of the placenta ruptures, leading to the characteristic appearance of a red, velvety membrane appearing at the vulva instead of the normal presentation of the foal within the amniotic sac. This condition is an emergency, as it can lead to a lack of oxygen (hypoxia) for the foal and poses a significant risk to its survival.

While the presence of meconium is a concern in some cases, it is not specifically indicative of a "red bag" delivery. Bright red mucous membranes can occur for various reasons and are not specific to this condition. The expulsion of the amniotic sac can happen during normal deliveries or in other pathological cases and does not exclusively indicate a "red bag" scenario. Thus, recognizing the signs of prematurity of the placental separation is crucial for timely intervention and care in affected mares.