The effect of chronic, mild heat stress on metabolic changes of nutrition and adaptations in rumen papillae of lactating dairy cows

Abstract

Global warming and accompanying high ambient temperatures reduce feed intake of dairy cows and shift the blood flow from the core of the body to the periphery. As a result, hypoxia may occur in the digestive tract accompanied by disruption of the intestinal barrier, local endotoxemia and inflammation, and altered nutrient absorption. However, whether the barrier of the rumen, like the intestine, is affected by ambient heat has not been studied so far. Lactating Holstein dairy cows were subjected to heat stress at 28°C (temperature-humidity index = 76; n = 5) with ad libitum feed intake or to thermoneutral conditions at 15°C (temperature-humidity index = 60; n = 5) and pair-feeding to heat-stressed animals for a total of 4 d. Gas exchange and feed intake behavior were measured in a respiration chamber, and rumen epithelia were taken after slaughter. Heat stress significantly reduced meal size and whole-body fat oxidation but increased meal frequency and carbohydrate oxidation. The mRNA expression of toll-like receptor 4 (TLR4) and tight junction proteins and the phosphorylation of TLR4 downstream targets (interleukin-1 receptorassociated kinase 4, stress-activated protein kinase, p38 mitogen-activated protein kinase, and nuclear factor k-B) in the rumen epithelium were not affected by heat. The proteomics approach revealed increased expression of rumen epithelium proteins involved in the AMP-activated protein kinase (AMPK) and insulin signaling pathways in heat-stressed cows. Also, proteins involved in chaperone-mediated folding of proteins were upregulated, whereas those involved in antioxidant defense system were downregulated. Further, we found evidence for increased carbohydrate phosphorylation accompanied with an increased flux of carbohydrates through the hexosamine biosynthetic pathway, provid-ing substrates for protein glycosylation. In conclusion, the mild heat stress did not induce barrier dysfunction or inflammatory responses in the rumen epithelium of dairy cows, probably because of adaptations in feed intake behavior and defense mechanisms at the tissue level.

Jejunal mucosa proteomics unravel metabolic adaptive processes to mild chronic heat stress in dairy cows

“…Wang et al (2017) reported that the heat shock proteins HSP90A, HSP90B, HSPA6 were upregulated in the liver of Holstein dairy cows in summer relative to spring season 51 . In an earlier study, we observed an upregulation of HSPH1 and HSPB1 in rumen papillae of HS compared to PF Holstein cows 52 , suggesting a common upregulation of HSPs in visceral organs under heat stress conditions. However, results obtained from a proteome analysis differed between hepatic and jejunal respiratory chain complexes.…”

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

“…However, slight perturbations in rumen fermentation can change the concentration of individual VFAs. Heat stress can increase the frequency of feed ingestion and drinking ( Eslamizad et al, 2020 ; Herbut et al, 2021 ). It is believed that such adaptations were the results of self-regulation in response to HS ( West, 2003 ).…”

“…The complex structure of the rumen papillae also plays an important role in defending against harmful substances in rumen fluid, however, the blood diversion from the viscera to the periphery might alter the ruminal epithelial morphology under heat stress ( Kregel, 2002 ; Lambert et al, 2002 ). Though a recent study showed that mild HS did not induce barrier dysfunction of the rumen papillae in lactating dairy cows probably owing to a defense mechanism and feeding adaptation ( Eslamizad et al, 2020 ). The damages of HS to the barrier function of ruminal epithelia in lactating dairy cows remain elusive.…”

Heat Stress-Mediated Activation of Immune–Inflammatory Pathways

“…Nonetheless, heat stress (40 °C 2 h/day for 3 days) reduces expression of TLR2 and TLR4 in the jejunum of rats [ 34 ]. In the ruminal epithelium of heat-stressed dairy cows (constant 28 °C for 4 days), activation of TLR4 or the downstream targets of TLR4 (such as IRAK4, p38MAPK, SAPK/JNK, and NF-κB) were not detected, suggesting that heat stress may not affect this segment of the GIT [ 88 ]. Collectively, these results suggest an immediate and direct effect of heat and possibly an indirect effect of lumen bacterial antigens on TLR pathway activation in the small intestine; however, conclusive results and the significance of these findings in the pathogenesis of heat-stressed animals have not been clearly defined.…”