Fecal Glucocorticoid Analysis: Non-invasive Adrenal Monitoring in Equids

Summary

Adrenal activity can be assessed in the equine species by analysis of feces for corticosterone metabolites. The method offers a non-invasive option to assess long term patterns in both domestic and free ranging horses. This protocol describes the enzyme linked immunoassay involved and the associated biochemical validation.

Abstract

Adrenal activity can be assessed in the equine species by analysis of feces for corticosterone metabolites. During a potentially aversive situation, corticotrophin releasing hormone (CRH) is released from the hypothalamus in the brain. This stimulates the release of adrenocorticotrophic hormone (ACTH) from the pituitary gland, which in turn stimulates release of glucocorticoids from the adrenal gland. In horses the glucocorticoid corticosterone is responsible for several adaptations needed to support equine flight behaviour and subsequent removal from the aversive situation. Corticosterone metabolites can be detected in the feces of horses and assessment offers a non-invasive option to evaluate long term patterns of adrenal activity. Fecal assessment offers advantages over other techniques that monitor adrenal activity including blood plasma and saliva analysis. The non-invasive nature of the method avoids sampling stress which can confound results. It also allows the opportunity for repeated sampling over time and is ideal for studies in free ranging horses. This protocol describes the enzyme linked immunoassay (EIA) used to assess feces for corticosterone, in addition to the associated biochemical validation.

Introduction

The method described aims to analyse corticosterone concentrations in equine feces in order to provide a non-invasive evaluation of adrenal activity. Measuring hypothalamic-pituitary-adrenal (HPA) axis activity is an accepted approach to study the response to potentially aversive situations in both captive and domestic species. The reference technique and the most widely used method is the use of blood plasma¹ however, alternate methods such as fecal analysis have been developed in order to overcome the stress induced by blood sampling itself and allow the ability to monitor free ranging species.

During an aversive situation, phy....

Protocol

Ethics statement: procedures involving field sampling and animal subjects have been approved by the School of Animal, Rural and Environmental Science (ARES) at Nottingham Trent University.

1. Collection of Fecal Samples

NOTE: Gloves should be worn when handling fecal samples and methanol. If there is a strong suspicion that an animal could be suffering from a zoonotic disease, protective clothing such as a lab coat should also be worn.

1. Collect the fecal samples as soon as possible (within min to a few hr) following defecation and place them into a sample bag. Take three to five subsamples of any defecated sample with a total weight of approxi....

Results

Domestic horses (n = 16, 8 mares, 8 geldings) with a mean age of 15 years (± 3) were grouped according to gender and subjected to four housing designs with increasing levels of social isolation (n = 4 horse/treatment). Housing 1 involved horses living in a herd environment, closely simulating their natural habitat. Housing 2 involved horses living in pairs in an indoor barn. Housing 3 involved horses housed alone in stables but with visual contact to other horses and housing 4 involved to.......

Discussion

Fecal corticosterone analysis provides a means of assessing long term patterns of adrenal activity in horses. The non-invasive nature of the method overcomes the confounding effects of other sampling methods used to assess adrenal activity including saliva and plasma analysis⁹. In addition the technique has a clear non-invasive advantage if studying free ranging horses.

There are several key points to discuss regarding this method and its appropriate use. A critical step in the prot.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Corticosterone antibody & HRP kit	Coralie Munro - UC Davis		No longer available through UC Davis - please see Arbor Assays
Cortisol antibody & HRP kit	Coralie Munro - UC Davis		No longer available through UC Davis - please see Arbor Assays
Corticosterone synthetic standard hormone	Sigma Aldrich	50-23-7	Harnful if ingested or with skin contact. Use in fume cupboard
Cortisol synthetic standard hormone	Sigma Aldrich	15087-01-1	Harmful if ingested or with skin contact. Use in fume cupboard
Methanol	Sigma Aldrich	67-56-1	Irritant. Use in fume cupboard
Sodium Bicarbonate	Sigma Aldrich	144-55-8	Irritant
Sodium Carbonate Anhydrous	Sigma Aldrich	497-19-8	Irritant
Sodium Phosphate Dibasic	Sigma Aldrich	7558-79-4	Irritant
Sodium Phosphate Monobasic	Sigma Aldrich	10049-21-5	Irritant
BSA	Sigma Aldrich	9048-46-8	Irritant
Tween 20	Sigma Aldrich	9005-64-5	Irritant
Citric Acid	Sigma Aldrich	77-92-9	Irritant
ABTS	Sigma Aldrich	30931-67-0	Irritant
Hydrogen Peroxide 30%	Sigma Aldrich	7722-84-1	Irritant
Sodium Chloride	Sigma Aldrich	7647-14-5	Irritant
Buffer capsules - pH 4	VWR	332732B
Buffer capsules - pH 7	VWR	332742D
Buffer capsules - pH 10	VWR	332762H
Hydrochloric Acid	Sigma Aldrich	435570	Irritant. Use in fume cupboard
Sodium Hydroxide	Sigma Aldrich	S5881	Irritant
Analytical balance	Fisher Scientific	BFS-525-010A
Air compressor
Centrifuge
Computer +printer
fridge-freezer
Drying apparatus
+tubing
Flammable liquid storagecabinet	VWR	649-002
Fume cupboard
Hot-plate stirrer	VWR	640-282
Microplate reader	VWR
Microplate washer	VWR
pH meter	VWR
Eppendorf Research® pipettes - multipack option 2	VWR
Pipette - 1,000 µl	VWR
Pipette - 200 µl	VWR
Pipette - 20 µl	VWR
Repeater pipette	VWR
Pipette filler	VWR
Orbital shaker	Progen Scientific
Sonicator	Hilsonic
Vortex	VWR
Warm water bath
Water purification system	Millipore