Our objective was to evaluate the effects of heat stress (HS) and dietary organic acid and pure botanical (OA/PB) supplementation on measures of hepatic inflammation and oxidative stress. Following a 7 d acclimation in thermoneutrality (temperature-humidity index [THI] 68), 46 Holstein cows were randomly assigned to 1 of 4 groups: thermoneutral conditions (TN-Con, n = 12), HS conditions (HS-Con, n = 12; diurnal THI 74 to 82), TN conditions pair-fed to match HS-Con (TN-PF, n = 12), or HS fed OA/PB (HS-OAPB, n = 10; 75 mg/kg of body weight; 25% citric acid, 16.7% sorbic acid, 1.7% thymol, 1.0% vanillin, and 55.6% triglyceride; AviPlus R; Vetagro S.p.A) for 14 d. Plasma was collected on d −1, 3, 7, and 14 and analyzed for serum-amyloid A (SAA) and reduced glutathione (GSH) concentrations. Liver was biopsied on d 12 and analyzed by transcriptomics (RNA-Seq). Data were analyzed using a mixed model including random effect of cow, and the fixed effects of treatment, time, and their interaction. Planned contrasts included HS-Con vs. TN-Con, HS-Con vs. TN-PF, and HS-Con vs. HS-OAPB. HS-Con had greater concentrations in plasma SAA (P < 0.01) and GSH (P < 0.08) concentrations relative to TN-Con, TN-PF, or HS-OAPB. Hepatic expression of genes related to inflammatory signaling (MYD88, SAA3, and NFKb1), were increased in HS-Con relative to TN-Con and TN-PF (P < 0.01) and HS-OAPB (P < 0.12). HS-OAPB tended to downregulate the initial enzyme in the transulfuration pathway (CBS; P = 0.06), while upregulated glutathione peroxidase 1 (GPX1; P = 0.01), relative to HS-Con. HS-Con overexpressed the taurine pathway (CDO1), relative to all treatments (P < 0.05). Regarding transmethylation pathway genes; AHCY and BHMT were upregulated in HS-Con compared with TN-Con and TN-PF (P < 0.01) and HS-OAPB (P < 0.07), while CHDH and MAT1A were downregulated in TN-PF compared with HS-Con (P < 0.01). Phosphatydilcholine degradation through GDPD5 was downregulated in HS-Con compared with all treatments (P < 0.04). Observed alterations at gene level may explain HS detrimental effects and suggest OA/PB supplementation as a means to improve hepatic health and metabolism.
Discover More: Sainz de la Maza-Escolà et al. (2023). ADSA Annual meeting 2023