Changes Associated with the Peri-Ovulatory Period, Age and Pregnancy in ACTH, Cortisol, Glucose and Insulin Concentrations in Mares

Abstract

Although there are many hormonal changes associated with reproduction, the effects of ovulation and early pregnancy on adrenocorticotropic hormone (ACTH) and insulin concentrations are poorly described. We hypothesise that both ovulation and early pregnancy will alter ACTH and insulin concentrations in healthy mares. Eighteen mares showing no clinical signs suggestive of, or laboratory findings consistent with, pituitary pars intermedia dysfunction PPID and insulin dysregulation (ID) are enrolled. ACTH, cortisol, insulin and glucose concentrations are measured over their peri-ovulatory period, as determined via ultrasounds and progesterone concentrations. The mares are grouped by age and gestation status, and a two-way repeated-measures ANOVA is used to determine the effects of age and early pregnancy, along with the peri-ovulatory period, on analyte concentrations. No significant effect of age, ovulation or early pregnancy is detected on the mares' cortisol, insulin or glucose concentrations; however, there is a significant effect of early pregnancy and ovulation on ACTH concentrations (p = 0.04 and p = 0.04 respectively). ACTH concentrations change around ovulation and with early pregnancy. Therefore, knowledge of a mare's reproductive status might be beneficial when interpreting ACTH concentrations.

Keywords: early pregnancy; endocrinology; equine; hypothalamic–pituitary–adrenal axis; insulin dysregulation; metabolism; oestrous cycle; pituitary pars intermedia dysfunction.

Figure 1

Mean ± standard deviation for immunoreactive plasma ACTH concentrations associated with early pregnancy and peri-ovulatory period, showing a significant effect of early pregnancy and time in the peri-ovulatory period upon the immunoreactive plasma ACTH concentration (p = 0.04 and p = 0.04, respectively). Purple discs indicate pregnant mares (n = 11), and black squares indicate non-pregnant mares (n = 7). The x-axis does not reflect the time scale.

Figure 2

Mean ± standard deviation for immunoreactive plasma ACTH concentrations associated with age and peri-ovulatory period, showing a significant effect of time in the peri-ovulatory period (p = 0.04). Purple discs indicate mares ≥ 12 years of age (n = 6), and black squares indicate mares <12 years of age (n = 12). * p < 0.05 14-day EPD vs. pre-ovulatory, regardless of the age of the mare. The x-axis does not reflect the time scale.