Progress report for GNE18-171
Objective 1: Define the gut-liver axis in lactating dairy cows experiencing leaky gut. Rationale: The gut-liver axis involves the complex interplay between the gut microbiota, intestinal permeability, systemic endotoxemia, and liver health. In non-ruminants, microbial dysbiosis promotes leaky gut and compromises health, and heat stress modulates the gut microbiome in broilers. Therefore, heat stress likely changes the bovine gut microbiome in dairy cows experiencing heat stress and leaky gut.
Objective 2: Determine whether rumen-protected OA/PB supplementation prevents endotoxemia and liver injury in lactating dairy cows experiencing leaky gut. Rationale: Leaky gut increases circulating endotoxin to promote hepatic steatosis, inflammation, and activation of the acute phase response. Feeding rumen-protected OA/PB may reduce intestinal permeability to minimize these outcomes. Therefore, dietary OA/PB supplementation may be a practical approach to improve gut and liver health in dairy cattle.
Enhanced intestinal permeability disrupts the intestinal barrier to culminate in microbial translocation into the host (Bischoff et al., 2014). Consequently, an increase in circulating gut-derived endotoxin promotes liver injury. Specifically, enhanced uptake of endotoxin by the liver promotes triglyceride accumulation, inflammation, and activates the acute phase response, which is a component of the innate immune system. We hypothesize that heat stress promotes dysbiosis of the dairy cow gut microbiota while enhancing intestinal permeability, endotoxemia, and liver injury. Moreover, we consider the possibility that rumen-protected OA/PB supplementation may restore the intestinal barrier, lower circulating endotoxin, and improve hepatic health in cows challenged by hyperthermia. To test our hypotheses, we will study lactating Holstein dairy cows housed in thermal neutral or heat stress environmental conditions. Our experimental design will include a pair-fed control housed in thermal neutral conditions with intake matched to cows experiencing heat stress. Such an approach will account for effects associated with changes in intake. Regarding our measurements, we will utilize a contemporary omics approach to characterize the fecal microbiome. Although leaky gut predominantly develops in the small intestine, we emphasize that the fecal microbiota is an adequate reflection of the intestinal microbiome (Barko et al., 2018). To measure intestinal permeability, we will quantify circulating levels of intestinal-fatty acid binding protein which is a biomarker of intestinal barrier dysfunction. Plasma endotoxin levels will be quantified to evaluate endotoxemia status. Circulating alanine aminotransferase, haptoglobin, and serum amyloid A will be measured to assess hepatic lipid accumulation, inflammatory status, and the acute phase response. Collectively, our approach will allow us the ability to characterize the gut-liver axis during heat stress and OA/B supplementation.
To investigate the effects of heat stress on the gut-liver-axis, gastrointestinal microbiome, and intestinal permeability we will enroll thirty-six mid-lactating multiparous pregnant Holstein cows in a CRD study. In blocks of eight, cows will be housed in temperature and humidity controlled environmental chambers with tie-stalls at the Cornell Large Animal Research and Teaching Unit (LARTU). Following acclimation (7-d), cows will be assigned to one of four treatments (14-d; Figure 1): (i) thermoneutral or (ii) heat stressed conditions, (iii) pair-fed in thermoneutral conditions to match the intake of heat stressed cows, or (iv) heat stressed with supplemental rumen-protected organic acids and plant botanicals (OA/PB; AviPlus R® at 75 mg/kg of BW per d; contains 25% citric acid, 16.7% sorbic acid, 1.7% thymol, 1% vanillin and 55% lipid encapsulate [for rumen protection]; Vetagro) as a top-dress. Cows not receiving OA/PB will be supplemented with an equivalent level of lipid encapsulate. Cows will be ad libitum fed or pair-fed a mixed ration that contains 1.7 Mcal of net energy for lactation/kg of dry matter. During the acclimation period, temperatures will remain at 24°C (temperature-humidity index [THI] = 68). For heat stress conditioning, temperatures will incrementally increase from 27°C at night (THI = 73) to 39°C in late afternoon (THI = 83). A 12- and 12-h light and dark cycle will be utilized. Cows will be milked twice daily. Blood, milk, and fecal sampling will be performed as described in Figure 1. The focus on OA/PB is warranted because of their potential to reduce intestinal inflammation and permeability in swine and reduce pathogenic bacteria.
The current project was approved by IACUC (Protocol #: 2018-0110). The project has started in August 2020 and is currently under the data collection phase with 66% of completion. The project will be completed in the Spring 2021 (as per revised timeline).
Phase 1, Sample Collection, Fall 2020/Spring 2021
December 2019: Obtain IACUC approval
August - December 2020: Enroll 4 blocks of 8 cows (n=32) in experiment and collect samples
January - March 2021: Enroll the remaining 2 blocks of 8 cows (n=16) in experiment and finalize sample collection
April - June 2021: Summarize feed, milk, body weight, respiration and heart rate, and body temperature data including statistical analysis.
Phase 2, Sample Analyses, Spring and Summer 2021
June-August: Complete sample analyses. Prepare manuscripts for Journal of Dairy Science.
Phase 3, Presentation of Findings, Summer 2021 and Fall 2021
June: Present final findings at ADSA and the Advanced Dairy Nutrition and Management Shortcourse.
June-August: Publish a PRODAIRY e-Leader newsletter or The Manager magazine article
August: Submit manuscripts for peer-review and submit final abstracts for ADSA annual meeting presentation.
October: Re-submit revised manuscripts for peer-review if requested.