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

Gemma R. Hicks,François-René Bertin,Natalie S. Fraser

doi:10.3390/ani11030891

Gemma R. Hicks, François-René Bertin + Show 1 more

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https://doi.org/10.3390/ani11030891

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Abstract

Simple SummaryThe reproductive cycle of mares is associated with many hormonal changes, but the effects of this cycle and pregnancy on adrenocorticotropic hormone and insulin concentrations are poorly described, which could limit our ability to diagnose pituitary pars intermedia dysfunction and insulin dysregulation. In this study, healthy mares are followed through their reproductive cycle during the physiologic breeding season, and adrenocorticotropic hormone, cortisol, glucose and insulin concentrations are measured to determine the effects of age, pregnancy and the reproductive cycle on analyte concentrations. No significant effect of age, the reproductive cycle or pregnancy is detected on the cortisol, glucose or insulin concentrations; however, adrenocorticotropic hormone concentrations are significantly increased throughout the peri-ovulatory period and during pregnancy. Therefore, knowledge of a mare’s reproductive cycle might be beneficial when interpreting adrenocorticotropic hormone concentrations.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.

Highlights

Considering the narrow range in body condition score (BCS), no further analysis was performed on this variable
There was no significant effect of early pregnancy and time in the peri-ovulatory period upon immunoreactive serum cortisol, immunoreactive serum insulin or blood glucose concentrations
The main results of this study are that (1) immunoreactive plasma adrenocorticotropic hormone (ACTH) concentration is altered throughout the duration of a mare’s peri-ovulatory period and that (2) early pregnancy results in a higher immunoreactive plasma ACTH concentration

Summary

Introduction

The hypothalamo–pituitary–adrenocortical (HPA) axis is the main control of the neurological and endocrine mechanisms, as it integrates external and internal stimuli. Several studies have identified the role of external environmental factors, such as season or diet, on adrenocorticotropic hormone (ACTH) secretion, as well as the role of critical illness on the HPA axis’ function [1,2,3]. Mares are seasonally polyoestrous breeders and undergo neuroendocrine changes throughout their peri-ovulatory period [4]. The mare’s cycle is a reflection of changes to multiple external and internal factors, such as days’ length, age, ovarian capacity and disease status [4]. The investigation of endocrinopathies in mares showing signs of reproductive failure—such as infertility, irregular peri-ovulatory periods or chronic uterine infections—is recommended; the effect of ovulation on this commonly measured hormone is poorly described

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