Placental Features and Newborn Viability in the Thoroughbred Horse

This study was aimed to characterize morphological findings of 29 placentas collected immediately after normal, spontaneous foaling and to evaluate newborn development and viability in thoroughbred horses. Morphological evaluation included complete placenta examination, gross lesion characterization and area measurement, and histopathological exam of selected area of placenta (pregnant and non-pregnant horn, cervical star, body and damaged area). According to gross lesion area, characteristics about villi, presence of fibrosis, oedema, inflammation and every other abnormal finding, the placentas were classified in four morphological classes (MC) from the best (class 1) to the worst (class 4). Foal viability was evaluated by APGAR test and by time to stand up and time for suckling record, while foals development was evaluated by body weight. Age of mares, pregnancy length, and characteristics of the early post-partum were also evaluated. Spearman correlation test was used to evaluate relationship among each parameter. Increased MC had a negative influence on APGAR index (p < 0.001), time to stand up of foals (p < 0.05), and with post-partum endometritis occurrence (p < 0.05). Increased allantochorion weight and area had a negative influence on time to stand up of the newborn (p < 0.05). In the same way, aged mare had a negative influence on time to stand up of foals (p < 0.05). The foal body weight was positively correlated with pregnancy length (p < 0.0001). In conclusion, morphological evaluation of placenta provides useful information about both newborn viability and endometritis occurrence in mares.