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

Factors affecting measurement of basal adrenocorticotropic hormone in adult domestic equids: A scoping review

Measurement of basal adrenocorticotropic hormone (ACTH) concentration is the most commonly used diagnostic test for pituitary pars intermedia dysfunction (PPID). Although several pre-analytical and analytical factors have been reported to affect basal ACTH concentrations in equids, the extent to which these have been evaluated in the context of PPID diagnosis is unclear. The objectives of this scoping review were to identify and systematically chart current evidence about pre-analytical and analytical factors affecting basal ACTH concentrations in adult domestic equids. Systematic searches of electronic databases and conference proceedings were undertaken in June 2022, repeated in October 2022 and updated in August 2023. English language publications published prior to these dates were included. Screening and data extraction were undertaken individually by the authors, using predefined criteria and a modified scoping review data extraction template. After removal of duplicates, 903 publications were identified, of which 235 abstracts were screened for eligibility and 134 publications met inclusion criteria. Time of year, exercise, breed/type and transportation were the factors most frequently associated with significant increases in ACTH concentration (n = 26, 16, 13 and 10 publications, respectively). Only 25 publications reported inclusion of PPID cases in the study population, therefore the relationship between many factors affecting basal ACTH concentration and diagnostic accuracy for PPID remains undefined. However, several factors were identified that could impact interpretation of basal ACTH results. Findings also highlight the need for detailed reporting of pre-analytical and analytical conditions in future research to facilitate translation of evidence to practice.

Age-Related Differences in Short-Term Transportation Stress Responses of Horses

Transportation of horses on short journeys can lead to an increase in stress. There are known age-associated changes in immune and metabolic responses in horses; however, no research exists evaluating how age may influence these responses to transportation stress. Eleven mares within two age groups, aged (n = 5, 22 ± 1 year) or young (n = 6, 2 ± 1 year), were transported 1 hour and 20 minutes. Peripheral blood and saliva were collected before and after transportation at baseline (2 to 3 weeks prior to transportation), 24 hours pre-transport, 1 hour before loading, 15 minutes, 30 minutes, 1 to 3 hours, 24 hours and 8 days post-transport. Heart rates, rectal temperatures, under the tail temperatures, serum cortisol, plasma ACTH, serum insulin, salivary cortisol and salivary IL-6 were measured. Whole blood gene expression of the cytokines IL-1b, IL-2, IL-6, IL-10, IFNγ, and TNFα were determined through qPCR, and peripheral blood mononuclear cells were isolated, stimulated, and stained to determine IFNγ and TNFα production. Serum cortisol (P < .0001), salivary cortisol (P < .0001) and heart rate (P = .0002) increased in response to transportation with no age differences. Rectal (P = .03) and under the tail temperatures (P = .02) were increased in young versus aged horses. ACTH was higher in aged horses (P = .007) and post-transportation (P = .0001). Aged horses showed a greater increase in insulin compared with young horses (P < .0001). While age does not seem to impact cortisol responses to short-term transportation in horses, it did influence the post transportation insulin response to stress in aged horses.

Successful Pregnancy Outcome in Mares: The Potential Role of Body Conditional Score, Age and Biochemical Parameter's Adjustments

The objective of this research was to evaluate the changes in body condition score (BCS), age and the main biochemical parameters in pregnant Spanish Purebred mares. A total of 45 pregnant Spanish broodmares has been studied, classified in three different groups: group A (n = 15), aging 14-18 years old and BCS lower than 4 of 10, group B (n = 15), with ages of 4 to 8 years and a BCS of 5-6/10, and group C (n = 15), aging between 6 and 11 years and a BCS of 8 of 10. Three pregnancy periods were considered: the 1st period, from the 1st to the 3rd, the 2nd from the 4th to the 6th, and the last period, from the 7th month of pregnancy to delivery. Blood samples were taken every month along the pregnancy. The following plasma biochemical parameters were measured: triglycerides, total cholesterol, high density lipoprotein-cholesterol, low density lipoprotein-cholesterol, total, direct and indirect bilirubin, aspartate aminotransferase, lactate dehydrogenase, γ-glutamyl transferase, alkaline phosphatase, total plasma proteins, albumin, glucose, urea and creatinine. Pregnancy in the Spanish broodmare induced hyperlipidemia with hypertriglyceridemia and increased plasma concentrations of total, direct and indirect bilirubin (P < .05). Older pregnant mares showed biochemical changes probably consistent with decreased organ functionality (P < .05). Obesity did not influence lipidic metabolism during pregnancy (P > .05).

Short-Term Effects of Temperature and Thyrotropin-Releasing Hormone Stimulation on Adrenocorticotropin Stability in Horses

Pituitary pars intermedia dysfunction (PPID) is diagnosed by increased basal or post thyrotropin-releasing hormone (TRH) stimulation ACTH concentrations. ACTH is known to be unstable; however, the effect of different temperatures and TRH stimulation on equine ACTH stability is poorly described. In total, 15 horses, including 8 PPID positive (ACTH > 35 pg/mL at baseline or >65 pg/mL 30 min after TRH stimulation), were divided into 2 groups: 9, including 5 PPID positive, with basal ACTH concentrations and 6, including 3 PPID positive, with post TRH stimulation ACTH concentrations. Whole blood was stored for 1 h at 4, 20, 30, 40, or 70 °C. After centrifugation, immunoreactive ACTH concentrations were determined using a chemiluminescent assay. Linear mixed effect models were used to detect the effects of temperature, PPID status, and TRH stimulation on the immunoreactive ACTH concentration. Temperature had a significant effect (p = 0.003) on immunoreactive ACTH concentrations, and this effect was greater in PPID-negative horses (p = 0.01), with the changes in immunoreactive ACTH concentrations being slightly unpredictably higher or lower than samples stored at 4 °C. Even at 20 °C, mean immunoreactive ACTH concentrations minimally changed by 5% in PPID horses and 12% in non-PPID horses after 1 h. No significant effect of TRH stimulation was identified. Although ACTH concentrations should ideally be determined from samples kept at 4 °C, samples inadvertently left at temperatures of up to 40 °C can provide valid results if analyzed within 1 h; however, this increases the risks of altered ACTH concentrations, occasionally influencing the diagnosis of PPID.

Repeatability of a thyrotropin-releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses

BACKGROUND

Pituitary pars intermedia dysfunction (PPID) is a common endocrinopathy of horses diagnosed with a thyrotropin-releasing hormone (TRH) stimulation test.

HYPOTHESIS/OBJECTIVES

Describe the repeatability of TRH stimulation in horses with and without PPID in winter and autumn.

ANIMALS

Twenty adult horses; 6 controls and 6 with PPID tested in autumn, 8 controls and 6 with PPID tested in winter with 3 controls and 3 with PPID tested in both seasons.

METHODS

Thyrotropin-releasing hormone stimulation was performed on 2 consecutive occasions, 1 week before and 1 week after the winter solstice and the autumn equinox. Blood was collected before and 30 minutes after IV injection of 1 mg of TRH. ACTH concentration was determined by a chemiluminescent assay. Repeatability and test-retest reliability were assessed by repeated measures analysis of variance, intraclass correlation coefficient and within-horse coefficients of variation (CV). Bland-Altman plots were generated to visualize agreement between repetitions.

RESULTS

In winter, no week effect was detected on the results of the TRH simulation and the test had an excellent test-retest reliability. In autumn, after-TRH ACTH concentrations were significantly lower on week 2 (P = .02) and the test only had a good test-retest reliability. There were significantly larger within-horse CV during autumn (P = .04) and after TRH stimulation (P = .04). There were 2 misclassifications in winter and 4 in autumn.

CONCLUSIONS AND CLINICAL IMPORTANCE

The TRH stimulation test was repeatable when performed 2 weeks apart in winter; however, in autumn, more variability in after-TRH ACTH concentrations resulted in decreased repeatability.