Cortisol as an Indicator of Stress in Animals Under Different Grazing Systems

Project Overview

Project Type: Graduate Student
Funds awarded in 2019: $13,500.00
Projected End Date: 08/31/2021
Grant Recipient: Virginia Tech
Region: Southern
State: Virginia
Graduate Student:
Major Professor:
John Fike
school of Plant and Environmental Sciences, Va Tech


  • Animals: sheep


  • Animal Production: animal protection and health
  • Crop Production: silvopasture


    Heat stress can compromise animal welfare and productivity, causing significant economic consequences. Many producers in the southeastern United States purchase expensive shade systems or allow livestock access to shaded streams to reduce heat load. Managing livestock in silvopasture systems can help reduce heat stress and improve animal behavior and productivity. Although gain typically is the default measure of animal well-being, it may not fully assess the effects of acute and chronic exposure to high temperature environments. Prolonged stress elevates cortisol in animals, and cortisol may be a good indicator of animal stress in different grazing systems. Blood is a common matrix for accessing cortisol levels in animals, but the sampling procedure requires capturing and restraining animals that itself increase the cortisol level, potentially confounding the reliability of the assessment. Hair cortisol is a relatively non-invasive and reliable measure of chronic stress, but it has received limited use especially in pasture systems. Hair cortisol reflects long-term chronic stress levels in animals ranging from several weeks to months depending on the length of hair and growth rate. It is a more reliable method of assessing stress as it is not influenced by the handling and restraining of animals during sampling procedures. In addition to being a relatively less invasive procedure, samples can be store at room temperature for a long time. In this study, we compared behavioral and physiological (temperature, hair, and blood cortisol) responses of ewes that grazed open pasture or black walnut (Juglans nigra) or honeylocust (Gleditsia triacanthos) silvopastures.  Thirty-six (36) Katahdin ewes were stratified by age, weight, and coat color, assigned to one of the treatments, and were rotationally stocked for a 6-week summer grazing trial. Among systems there was no difference in body weight gains for these mature animals. However, ewes grazing OP showed signs of heat stress as they spent more time loafing and less time lying down compared to ewes on silvopasture treatments. This was measurable, too, as ewes on open pasture had 0.5-1.0°C (0.9-1.8°F) hotter intravaginal temperatures between 1200h-1700h than ewes on silvopasture treatments. Measures of plasma cortisol were not different by treatment. However, measures of hair cortisol worked well for determining differences in this stress hormone. Ewes in the open pastures had greater hair cortisol levels than ewes in silvopasture treatments. Trees within the silvopastures moderated ambient conditions, thus reducing stress and improving the behavioral and physiological responses. Hair cortisol can be a reliable and relatively non-invasive method of assessing long-term chronic stress.

    Project objectives:

    To compare the behavioral and physiological responses of ewes in black walnut- (Juglans nigra) and honeylocust- (Gleditsia triacanthos) based silvopastures with that of ewes in open pasture using minimally-invasive measures – specifically, hair cortisol and intravaginal temperature loggers.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.