Assessment of equine alpha-fetoprotein levels in mares and newborn foals in the periparturient period

Alpha-fetoprotein (AFP) is best known in human obstetrics for its association with fetal anomalies recognized in the 1970s. Although this fetal protein had been shown to be present in the sera of many mammalian species, its possible diagnostic role in the detection of abnormalities was evaluated only later, when a research laboratory published variable levels of AFP in different groups of mares with pregnancy problems (twins, conception failure, placentitis, embryonic loss), and subsequently differences were demonstrated in its serum levels between aborted and healthy mares. In this study, peri- and intrapartal AFP levels were measured in maternal serum, amniotic fluid, neonatal blood, and umbilical blood samples. The mean levels of AFP were lower in umbilical blood and amniotic fluid samples than in foal and maternal blood. Older mares had lower AFP levels correlated with their age in years. The time remaining until foaling had a significant, non-linear effect on AFP levels: an elevation could be detected in the last two weeks of pregnancy, followed by a decline after foaling. Also, AFP levels were found to be elevated in the hot summer months. There was a significant individual variation in AFP levels in the population studied.