Author ORCID Identifier

https://orcid.org/0009-0002-2637-7343

Date Available

10-16-2025

Year of Publication

2025

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College

Agriculture, Food and Environment

Department/School/Program

Animal and Food Sciences

Faculty

Leslie H. Anderson

Faculty

Eric S. Vanzant

Abstract

Data from year one of a three-year experiment was used to determine behavioral and physiological responses of heifers adapted to grazing endophyte-infected fescue (E+TF) compared to heifers naïve to grazing E+TF. In May, yearling beef heifers from KY (n=15) and MT (n=30) were stratified by body weight, hair coat score, and disposition into nine pastures and assigned to one of three treatments: KY grazing E+ (KY-E+), MT grazing E+ (MT-E+), or MT grazing endophyte-free tall fescue (E-TF) (MT-E-). Prior to grazing, two heifers per pasture were selected to be outfitted with a RumiWatch® halter (Itin+Hoch GmbH, Liestal, Switzerland) for monitoring of grazing and rumination behavior. Halters were utilized during five periods throughout the grazing season. Additionally, all heifers were outfitted with a Smart Rumen Bolus (Moonsyst, Agri IOT LIMITED, Kilkenny, Ireland) for continuous monitoring of reticulorumen temperature and a CowManager Sensor (Agis Automatisering, Harmelen, the Netherlands) ear tag for estrus detection. Respiration rates and weather data were collected to determine the influence of ambient conditions. Animal body weights and reproductive status were measured monthly to determine differences in animal performance. All pre-processing of data was completed with Python (v. 3.11.11) using NumPy (v. 1.26.4) and Pandas (v. 2.3.3) packages. Data were analyzed using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC). In chapter four, data for respiration rate as well as grazing and rumination behavior were analyzed. Adaptation to environment, forage, and management was indicated by no differences between KY-E+ and MT-E+. KY-E+ spent less time ruminating daily (P < 0.05) than MT-E+ during period one. MTE+ spent more time grazing (P < 0.05) than KY-E+ through period two. Respiration rates differed (P < 0.05) through the entirety of the trial between KY-E+ and MT-E+ as well as MT-E+ and MT-E-. If adaptation is determined by rumination behavior, our findings suggest adaptation takes approximately one month. However, if grazing behavior is the metric to determine adaptation, approximately two to three months are required. Use of respiration rate to gauge adaptation suggests that after the five observation periods throughout the grazing trial, naïve heifers were not adapted to the local environment or grazing E+TF. Further investigation into the physiological mechanisms driving these behaviors as well as future replication may give additional insight into these differences in adaptation. In chapter five, the ability of environmental measures to predict heat stress responses were evaluated. In this study, ambient temperature provided the highest level of accuracy (P < 0.05) for predicting heat stress based on physiological responses of grazing beef cattle of different origins, regardless of the forage they were consuming. Breakpoints were used to determine the temperature necessary to invoke increased respiration rates. The breakpoint in period one was 16°C and increased to 21°C by period five. Additionally, respiration rates decreased (P < 0.05) from period two to three. Together, these findings suggest adaptation over the summer. Although adaptation occurred, MT-E+ had a greater (P < 0.05) slope for reticulorumen temperature in relation to ambient temperature than KY-E+, suggesting cattle adapted to E+TF consumption are less influenced by ambient conditions. The findings of this thesis could be used to develop mitigation strategies for fescue toxicosis and heat stress while naïve animals are adapting, as well as identify animal tolerant to E+TF consumption. Due to the variability of animal responses and season, further research is warranted.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.452

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