UNDERSTANDING THE RUMEN-MICROBIOTA-BRAIN AXIS OF LACTATING DAIRY COWS UNDER HEAT STRESS

Our long-term goal is to develop practical strategies targeting the rumen-microbiota-brain axis to alleviate animal stress and improve animal welfare. The central hypothesis for this project is that there is a rumen-microbiota-brain axis that modulates heat stress responses. Specifically, the rumination behaviors and microbial communityare influencedwhen the hypothalamus senses high temperature and sends the signal to the rumen via the nervous system. The shifted rumen environment and microbiota may transmit information to the central nervous system (CNS) and enteric nervous system (ENS) through host and bacteria-produced neurotransmitters that activate neurotransmitter receptors and regulate stress responses.The specific aim of this study isto understand the heat stress-related crosstalk between rumen microbiota, enteric nervous system, and central nervous system in lactating cows.Based on the literature review and our previous studies, we hypothesize that colonization of specific bacterial species in the rumen of Holstein lactating cowsis influencedby heat stress (Obj. 1). The shifted rumen microbiota will affect host and bacteria-derived neurotransmitters and interact with downstream neurotransmitter pathways in CNS and ENS (Obj. 2). The crosstalk between rumen and nervous system via microbiota and neuroactive substances is different between heat-tolerant Jersey cows and heat-susceptible Holstein cows, partly explaining the advantage of Jersey cows in dealing with heat stress (Obj. 3). The objectives are as follows:Objective 1: Identify specific heat stress-associated ruminal microbial species and genes in Holstein lactating cows using the high-resolution long-read sequencing technologyObjective 2: Detect the influence of heat stress on neuroactive substances and neurotransmitter pathways in the rumen and nervous system of Holstein lactating cowsObjective 3: Investigate the uniqueness of the rumen-microbiota-brain axis in heat-tolerant Jersey cows compared to heat-susceptible Holstein cows