Impact of water intake on reticulorumen temperature dynamics and microbial diversity in cattle

Abstract

The quest for highly efficient cattle has become increasingly important as demand for animal-sourced food rises under the threat of global warming. Improving cattle productivity and sustainability requires a deeper understanding of reticulorumen temperature (RT) dynamics and their influence on microbial fermentation. Although water intake evokes a rapid decline in RT, the impact of these thermal fluctuations on microbial community composition and fermentation efficiency remains poorly understood. Based on the links between water intake and RT dynamics, this thesis aims to investigate reticulorumen thermoregulation using thermodynamic principles and assess its impact on microbial fermentation. A comprehensive literature review first examined the physicochemical and microbial environment of the reticulorumen, highlighting the impact of water intake on RT variability. Subsequent thermodynamic analyses of published RT data showed that colder water caused greater RT declines, supporting the predictive utility of thermodynamic principles for RT dynamics. Using sensor-driven RT data from feedlot cattle, individual variation in drinking frequency, RT decline magnitude, and recovery duration was then characterised. An in vitro model was subsequently developed to simulate RT fluctuations associated with drinking events under controlled conditions. Using this model, short-term RT fluctuations were shown to influence fermentation kinetics and microbial composition in a substrate-dependent manner, with frequent temperature drops delaying early fermentation and altering microbial diversity and fermentation profiles. Overall, this thesis identifies drinking-associated RT fluctuations as an overlooked factor influencing rumen microbial community diversity and fermentation. By linking drinking behaviour, RT dynamics, and microbiome responses, the findings provide a foundation for microbiome-informed strategies to improve cattle productivity and environmental sustainability.