Postnatal Dynamics of Circulating Steroid Hormones in Mule and Equine Neonates

SIMPLE SUMMARY: Neonatal pathologies are extremely important, such as neonatal maladaptation related to hormonal dysregulation in foals. As mules are becoming more popular, there is an increased demand for information on their health, including normal hormonal profiles of mule foals during the perinatal period and how it differs from equine foals. This study evaluated hormones (pregnanes, corticoids, and androgens) that are related to foal physiological development and maturation during the time neonates adapt to extra-uterine life; in mule and equine foals during their first 12 h after birth. Our findings suggest that there might be differences in the hormonal milieu between mule and horse foals, which might be related to the different placentation and uterine environment during hybrid pregnancies. Additionally, the pattern of hormones shows that there are derived from different tissues. These results can assist veterinarians with early diagnosis and intervention of neonatal mules with hormonal imbalances. ABSTRACT: It is necessary to study hormonal patterns from mules to recognize alterations and neonatal maladaptation. Our objective was to evaluate concentrations of hormones in mule (n = 6) and equine foals (n = 6). Blood was collected at T0, 1, 6 and 12 h after birth. Hormone concentrations were evaluated using liquid chromatography tandem mass spectrometry. Effects of time, group and interactions and regression analysis were evaluated (p < 0.05). There was a cubic and quadratic decline in mule and equine foals, respectively, for 3β,20α-dihydroxy-DHP. Mule foals were born with lower circulating 3β,20α-dihydroxy-DHP concentrations, which might be related to progestogen concentrations in mares with a hybrid placenta. Corticosterone and cortisol concentrations remained unchanged for the first hour post-foaling then declined in mule and equine foals (p < 0.0001). Dehydroepiandrosterone was the main androgen present. There was a decrease in dihydrotestosterone at 12 h (p = 0.002). Differences in the temporal patterns of secretion within each steroid class, pregnanes, corticoids, and androgens, suggest they were derived from different tissue sources, presumptively the placenta, adrenals and gonads of the fetus/neonate, respectively. Mule and horse foals were born without evidence of testosterone secretion. For the first time, steroid hormone levels were measured in neonatal mules, and this will provide insight into neonatal physiology that differs from equine and allow us to gain an understanding of mules that have rarely been studied. Further studies are needed to elucidate the effects of hybrid pregnancies in the steroid endocrinology of neonates.