Effect of endophyte-infected tall fescue on hepatic gene expression in cattle

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Fescue toxicosis may result from the intake of ergot alkaloids found in endophyteinfected (E+) tall fescue. The liver if the major organ involved in the pathology of fescue toxicosis, as it is the site where the toxic ergot alkaloids are metabolized. A study performed with rats consuming and E+ diet reported increased expression of Phase I detoxification enzymes and a decreased expression of antioxidants, to suggest an increase of cellular oxidative stress. This study was performed to determine if intake of E+ fescue had the same effect on the expression of detoxification enzymes and antioxidants in cattle. A second objective of this study was to examine changes in the hepatic transcriptome that occur when cattle consume E+ fescue. Missouri- (MO; n=10; 513.6±1.3 Kg BW) and Oklahoma- (OK; n=10; 552.8±12.0 Kg BW) derived Angus steers, maintained at 19-22°C (TN) air temperature for 8 days and then maintained at cycling heat stress for an additional 10 days (26°C night Ta; 36°C day Ta:HS). Cattle were fed diets containing either endophyte-free (E-) or E+ seed (30 [microgram] ergovaline/Kg BW/day) and feed intake (FI) was recorded daily. Blood and liver tissue samples were collected during pretreatment followed by blood samples at Day 4, 11, and 17 and liver tissue samples were collected again on Day 7 and 18. Consumption of E+ fescue resulted in significantly reduced (p!0.05) feed intake in both the TN and HS periods when compared to the E- group. There was also a significantly (p!0.05) lower serum prolactin concentration of E+ steers when compared to E- steers in both the TN and HS periods. These results confirm that E+ steers were experiencing the physiological conditions associated with fescue toxicosis. Real-time PCR was performed to determine expression of selected hepatic Phase I detoxification enzymes and specific antioxidant proteins. Illumina deep sequencing was performed on TN samples from selected fescue-naïve OK steers. Tiling of the sequences to a ̃23,500 member