Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/12/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Heat stress significantly impacts animal welfare, increases disease incidence, alters milk composition, and reduces reproductive performance. High-producing dairy cattle are especially affected, resulting in massive economic losses. Most research has focused on physiological or behavioral metrics of heat stress and there is limited investigation into the molecular mechanisms underlying heat stress. The aims of this proof-of-concept study were to demonstrate that dairy cow microbiomes are impacted by heat stress and that this can be measured by sampling cows in periods of heat stress and thermoneutral conditions. A cohort of 20 cows at the University of Connecticut research dairy were followed through Spring (representing pre-heat stress), Summer (heat stress), and Fall (post-heat stress), in 2023. Cow feces and milk were sampled in each season and initially characterized by 16S rRNA gene profiling on the Illumina Platform. Seasonal impacts on microbiome diversity were observed in both milk and feces. Concerning milk, Pielou’s Evenness was higher in Fall than in Spring or Summer (P < 0.01) and measures of Faith’s phylogenetic diversity suggest that Spring may be less diverse than Summer or Fall (P ~ 0.10). Bray-Curtis and weighted Unifrac distances indicate that Spring and Summer microbial composition are highly similar, but Fall is divergent from both (P < 0.05). Concerning feces, Pielou’s evenness did not differ between Fall and Summer, but Spring evenness was lower than both (P = 0.02 and P < 0.01, respectively). Analysis of Faith’s phylogenetic diversity suggested fecal microbial composition in the Spring is much less diverse than in the Fall or Summer (P < 0.001). Unweighted Unifrac pairwise PERMANOVA analysis suggested that Fall and Summer fecal microbiomes are highly similar, but Spring is divergent (P < 0.01) and tightly clustered in Emperor plot visualization. We conclude that substantial variation in milk and fecal microbiomes are observable over seasons representing different heat stress conditions and further hypothesize that this has a profound effect on the production and health losses described earlier. This study provides the basis for a multi-omics approach to unravel individual responses to heat stress that will provide opportunity to develop novel intervention strategies and enhance heat tolerance breeding strategies. As a result of this work, a multi-institutional research initiative is underway that aims to integrate dairy cow microbiome and transcriptome data to associate differentially expressed genes with prevalent microbes at multiple body sites in normal v. heat stressed conditions.