Effects of Heat Stress on the Ruminal Epithelial Barrier of Dairy Cows Revealed by Micromorphological Observation and Transcriptomic Analysis

Abstract

Heat stress (HS) alters the rumen fermentation of dairy cows thereby affecting the metabolism of rumen papillae and thus the epithelial barrier function. The aim of the present study was to investigate if HS damages the barrier function of ruminal epithelia. Eight multiparous Holstein dairy cows with rumen cannula were randomly equally allocated to two replicates (n = 4), with each replicate being subjected to heat stress or thermal neutrality and pair-feeding in four environmental chambers. Micromorphological observation showed HS aggravated the shedding of the corneum and destroyed the physical barrier of the ruminal epithelium to a certain extent. Transcriptomics analysis of the rumen papillae revealed pathways associated with DNA replication and repair and amino acid metabolism were perturbated, the biological processes including sister chromatid segregation, etc. were up-regulated by HS, while the MAPK and NF-kB cell signaling pathways were downregulated. However, no heat stress-specific change in the expression of tight junction protein or TLR4 signaling was found, suggesting that HS negatively affected the physical barrier of the ruminal epithelium to some extent but did not break the ruminal epithelium. Heat stress invoked mechanisms to maintain the integrity of the rumen epithelial barrier by upregulating the expression of heat shock protein and repairments in rumen papillae. The increase in amino acid metabolism in rumen papillae might affect the nutrient utilization of the whole body. The findings of this study may inform future research to better understand how heat stress affects the physiology and productivity of lactating cows and the development of mitigation strategies.

Protective Effects of Niacin on Rumen Epithelial Cell Barrier Integrity in Heat-Stressed Beef Cattle

“…Our findings from the micromorphological analysis that heat stress aggravates cuticle shedding and contributes to the disruption of the physical barrier of the rumen epithelium are consistent with those of a previous study [4]. Heat stress caused detrimental alterations to the tissue structure of the rumen epithelium and particularly resulted in cuticle degradation.…”

“…Heat stress disrupts the metabolism of rumen papillae and alters the rumen fermentation of the beef cattle, which subsequently affects the epithelial barrier function [4]. Micromorphological observations have suggested that heat stress exacerbates the exfoliation of the stratum corneum, leading to the destruction of the rumen epithelium's physical barrier [4]. Therefore, ensuring the homeostasis of ruminal epithelial barrier function is crucial for the health of ruminants.…”

Postnatal Growth and Development of the Rumen: Integrating Physiological and Molecular Insights

“…Probiotics such as Lactobacillus plantarum MB452 also enhance the barrier function of the rumen epithelium by increasing the expression of tight junction genes [68]. Heat stress affects the rumen epithelial barrier negatively to some extent but does not completely disrupt it, due to the upregulation of heat shock proteins [69]. In essence, the strength of the physical barrier of the rumen is intricately linked with the microbes and immune cells in the rumen.…”

Heat stress effects on the lactation performance, reproduction, and alleviating nutritional strategies in dairy cattle, a review

“…Under HS circumstances, the acetate-producing bacteria Actinobacteria and Acetobacter shrank (Kim et al 2022). Heat stress alters the rumen fermentation of dairy cows, affecting the rumen papillae's metabolism and, thus, the epithelial barrier function (Guo et al 2022). Zhao et al (2019) reported that heat stress resulted in the reduction of pH and acetate levels in the rumen; however, heat stress resulted in an increase in lactate levels in the rumen.…”