Influence of Maternal Age and Parity on Placental Structure and Foal Characteristics From Birth up to 2 Years of Age

The foal's weight and height at birth are regarded as important parameters for the equestrian sports industry. Moreover, scientific studies indicate that maternal environment can influence postnatal genetic potential of foals. The purpose of this study was to evaluate the influence of maternal age and parity on placental efficiency and size of the newborn foal using stereological analysis tools of the term's allantochorion. Furthermore, the influence of maternal age and parity on weight, height, and girth circumference of the offspring from birth until 2 years of age was investigated. Forty pregnant mares were categorized according to age: 4-8 years (n = 15); 9-12 years (n = 15); ≥13 years (n = 10) and parity: nulliparous (n = 12), 1-3 parities (n = 18); ≥4 parities (n = 10). Parturition was monitored and the allantochorion membranes were collected after delivery. The stereological analysis determined the volumetric composition of the different compartments of the placenta along with the area of fetomaternal contact surface. It was observed that maternal age and parity significantly increased the development of the microcotyledons and total villi surface density, as well as the vascularization and tissue composition of different regions of the placenta, which contributes to fetomaternal contact. We also found a significant relationship between maternal age and parity on the size of the neonate foals but not after the first year of age, possibly because environmental and genetic factors contribute to postnatal growth.