Neonatal glucocorticoid overexposure alters cardiovascular function in young adult horses in a sex-linked manner.

Prenatal glucocorticoid overexposure has been shown to programme adult cardiovascular function in a range of species, but much less is known about the long-term effects of neonatal glucocorticoid overexposure. In horses, prenatal maturation of the hypothalamus-pituitary-adrenal axis and the normal prepartum surge in fetal cortisol occur late in gestation compared to other precocious species. Cortisol levels continue to rise in the hours after birth of full-term foals and increase further in the subsequent days in premature, dysmature and maladapted foals. Thus, this study examined the adult cardiovascular consequences of neonatal cortisol overexposure induced by adrenocorticotropic hormone administration to full-term male and female pony foals. After catheterisation at 2-3 years of age, basal arterial blood pressures (BP) and heart rate were measured together with the responses to phenylephrine (PE) and sodium nitroprusside (SNP). These data were used to assess cardiac baroreflex sensitivity. Neonatal cortisol overexposure reduced both the pressor and bradycardic responses to PE in the young adult males, but not females. It also enhanced the initial hypotensive response to SNP, slowed recovery of BP after infusion and reduced the gain of the cardiac baroreflex in the females, but not males. Basal diastolic pressure and cardiac baroreflex sensitivity also differed with sex, irrespective of neonatal treatment. The results show that there is a window of susceptibility for glucocorticoid programming during the immediate neonatal period that alters cardiovascular function in young adult horses in a sex-linked manner.

Impact of equine assisted reproductive technologies (standard embryo transfer or intracytoplasmic sperm injection (ICSI) with in vitro culture and embryo transfer) on placenta and foal morphometry and placental gene expression.

Assisted reproductive technologies (ARTs) such as intracytoplasmic sperm injection (ICSI), in vitro embryo culture and embryo transfer (ET) may be associated with alterations in fetal and placental development. In horses, ET has been used for decades. More recently, in vitro embryo production by ICSI and in vitro culture, followed by embryo transfer (ICSI-C) has become an accepted method for clinical foal production. However, no information is available on the effects of ICSI-C or even of standard ET itself on placental and neonatal parameters in horses. We therefore evaluated placental and neonatal morphology and placental gene expression in reining- and cutting-type American Quarter Horse foals produced using different technologies. Thirty foals and placentas (naturally conceived (NC), ET and ICSI-C; 10 in each group) were examined morphometrically. The only parameter that differed significantly between groups was the length of the foal upper hindlimb, which was longer in ET and ICSI-C than in NC foals. Evaluation of placental mRNA expression for 17 genes related to growth and vascularisation showed no difference in gene expression between groups. These data indicate that within this population, use of ARTs was not associated with meaningful changes in foal or placental morphometry or in expression of the placental genes evaluated.