Non-Invasive Techniques Reveal Heifer Response to Fescue Endophyte Type in Grazing Studies

SIMPLE SUMMARY: This study compared the behavioral and physiological responses of heifers that grazed tall fescue infected with either a wild-type (WE) or a novel (non-toxic) endophyte (NE) using relatively non-invasive techniques such as hair cortisol, infrared cameras for extremities (ear, tail, and foot) temperatures, small loggers for intravaginal temperature, and remote imagery for monitoring animal behavior. Heifers on WE had cooler extremities temperatures and hotter intravaginal temperatures compared to those on NE. Hair cortisol levels were higher in heifers on WE compared to those on NE. Heifers on WE spent more time standing up and less time lying down during the daytime compared to those on NE. Overall, the findings indicate that replacing WE tall fescue with NE tall fescue can reduce heat load and corresponding stress in heifers, as indicated by changes in behavior, temperature, and cortisol levels. This study highlights the potential of non-invasive techniques such as thermographic imaging and hair cortisol analysis for assessing animal responses to stress in extensive grazing systems. ABSTRACT: Cattle grazing tall fescue (Schedonorus arundinaceous) infected with wild-type endophytes (WE) leads to a syndrome commonly known as fescue toxicosis. Replacing WE tall fescue with a novel endophyte-infected (NE) tall fescue can mitigate this problem but adoption of this technology has been limited. This study measured and determined the physiological and behavioral responses of heifers that grazed either WE or NE tall fescue, utilizing relatively non-invasive techniques including hair cortisol, thermography (for extremity temperatures), small loggers for intravaginal temperature, and remote observation of in-field behavior. Heifers that grazed WE had greater (p < 0.0001) hair cortisol levels, lower extremity temperatures (p ≤ 0.0075), and 0.3–0.9 °C greater (p ≤ 0.02) intravaginal temperatures (particularly during the daytime) than heifers that grazed NE. From 1200 h–1700 h each day, heifers on WE pastures spent 1.5 more (p = 0.0003) hours standing up and 0.9 fewer (p = 0.0402) hours lying down than heifers on NE pastures. Differences (p = 0.0160) in ADG were small (0.1 kg d(−1)) and were only observed in the first year of these 8-week studies. However, even in the mild environment of the study site, grazing NE tall fescue provided clear welfare benefits as evidenced by heifer behavioral changes, temperature differentials, and hair cortisol levels. This study underscores the potential utility of non-invasive techniques, such as thermographic imaging and hair cortisol analysis, for evaluating animal responses to stress in extensive grazing systems.