Honors Theses and Capstones

Date of Award

Spring 2025

Project Type

Capstone

College or School

COLSA

Department

Animal Science

Program or Major

Animal Science

Degree Name

Bachelor of Science

First Advisor

claira seely

Abstract

This study aimed to (1) investigate the association between Temperature-Humidity Index (THI) and rumination activity patterns in lactating dairy cows, and (2) explore the breed-specific impacts of THI on rumination time in Holstein and Jersey cows. The first hypothesis was that higher THI values would be associated with decreased rumination time (RT). The second hypothesis proposed that Holsteins, due to their lower heat tolerance, would experience greater reductions in RT than Jerseys under heat stress. From June 1 to October 1, 2024, daily climatic data were collected in New Hampshire using VisualCrossing to calculate THI. Each day was categorized into one of four heat stress levels: No heat stress (THI ≤ 68), Mild (69 < THI ≤ 72), Moderate (72 < THI ≤ 80), and Severe (THI > 80). RT was measured using SCR ear-mounted sensors on Holstein (n = 44) and Jersey (n = 8) cows on a single farm. ANOVA was used to assess the effects of THI, breed, and parity on RT, with breed-matched comparisons conducted to evaluate differences between Holsteins and Jerseys. Results supported the first hypothesis: RT significantly declined with increasing THI (P < 0.001), especially during Severe heat stress days. However, contrary to the second hypothesis, Jerseys showed a greater sensitivity to heat, with a more pronounced reduction in RT than Holsteins. These findings confirm a negative relationship between THI and rumination in dairy cows and highlight breed-specific behavioral differences. Continuous RT monitoring may aid early detection of heat stress and improve herd management strategies.

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