Effects of fescue toxicosis induced by endophyte-infected tall fescue seed on forestomach epithelial gene expression in Angus steers

Abstract Text:

A previous report demonstrated that steers exposed to an endophyte-infected tall fescue seed extract had altered rumen epithelial blood flow and decreased ruminal flux of VFA. Thus, this study was conducted to determine whether there are differences in gene expression related to VFA absorption between steers dosed with endophyte-infected (E+; 4.45 mg ergovaline/kg) or endophyte-free (E-) tall fescue seed. Twelve ruminally cannulated Angus steers (BW = 547 ± 9 kg) were stratified based on BW and randomly allocated to 6 blocks. The steers were fed alfalfa cubes at 1.5 x NE_m and dosed (1 kg/d) with ground tall fescue seed via rumen cannula once daily for 21 d. On d 22, the steers were slaughtered and tissue samples were immediately collected from rumen, reticulum, omasum, and abomasum. Samples were rinsed extensively with ice-cold physiological saline to remove residual feed and contents before separating epithelia from the underlying tissue. Thereafter, samples of epithelial tissue (1 g) were immediately homogenized with TRI-reagent. The expression levels of monocarboxylate transporter 1, 2, and 4 (MCT1, MCT2, and MCT4, respectively), sodium hydrogen exchanger 1, 2, and 3 (NHE1, NHE2, and NHE3, respectively), putative anion transporter 1 (PAT1), down regulated in adenoma (DRA), anion exchanger 2 (AE2), sodium bicarbonate cotransporter 1 (NBC1), 3-hydroxy 3-methylglutaryl coenzyme A synthase 2 (HMGCS2), and sodium potassium ATPase pump 1 (ATP1) were measured using SYBR-Green and abundances were quantified by qPCR using glyceraldehyde-3-phosphate dehydrogenase as the control gene. The levels of MCT1 and MCT4 expression were lower (P < 0.05) in the rumen tissue of steers dosed with E+ seed, whereas MCT2 was not different. The expression of NHE2 was lower (P < 0.05) for E+ steers, whereas NHE1 and NHE3 were not affected by seed in the rumen epithelium. The levels of DRA and AE2 expression were lower (P < 0.05) for E+ steers in the rumen epithelium, whereas PAT1, NBC1, HMGCS2 and ATP1 were not affected by seed treatment. Expression of these genes in reticulum, omasum, and abomasum epithelia, were not affected (P > 0.05) by seed treatment. These data indicate that endophyte-infected tall fescue seed may contribute to depression of ruminal VFA absorption in a dissociated state (pH > 5.8) by the depression of MCT1 and MCT4 in the rumen associated with NHE2, DRA and AE2. Consequently, this may contribute to decreased gain associated with fescue toxicosis in cattle.

Keywords: VFA transporter, gene expression, tall fescue