Ergot alkaloids from endophyte-infected tall fescue decrease reticuloruminal epithelial blood flow and volatile fatty acid absorption from the washed reticulorumen

An experiment was conducted to determine if ergot alkaloids affect blood flow to the absorptive surface of the rumen. Steers (n = 8) were pair-fed alfalfa cubes and received ground endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum; E+) seed (0.015 mg ergovaline·kg BW^-1·d^-1) or endophyte-free tall fescue (E-) seed via the rumen cannula 2x daily for 7 d at thermoneutral (TN; 22°C) and heat stress (HS; 32°C) conditions. On d 8, the rumen was emptied and rinsed. A buffer containing VFA was incubated in the following sequence: control (CON), 15 μg ergovaline·kg BW^-1 (1×EXT) from a tall fescue seed extract, and 45 μg ergovaline·kg BW^-1 (3×EXT). For each buffer treatment there were two 30-min incubations: a 30-min incubation of a treatment buffer with no sampling followed by an incubation of an identical sampling buffer with the addition of Cr-EDTA and deuterium oxide (D₂O). Epithelial blood flow was calculated as ruminal clearance of D₂O corrected for influx of physiological water and liquid outflow. Feed intake decreased with dosing E+ seed at HS but not at thermoneutral conditions (TN; P < 0.02). Dosing E+ seed decreased serum prolactin (P < 0.005) at TN. At HS, prolactin decreased in both groups over the 8-d experiment (P < 0.0001), but there was no difference in E+ and E- steers (P = 0.33). There was a seed treatment × buffer treatment interaction at TN (P = 0.038), indicating that E+ seed treatment decreased reticuloruminal epithelial blood flow at TN during the CON incubation, but the two groups of steers were not different during 1×EXT and 3×EXT (P > 0.05). Inclusion of the extract in the buffer caused at least a 50% reduction in epithelial blood flow at TN (P = 0.004), but there was no difference between 1×EXT and 3×EXT. There was a seed × buffer treatment interaction at HS (P = 0.005), indicating that the reduction of blood flow induced by incubating the extract was larger for steers receiving E- seed than E+ seed. Volatile fatty acid flux was reduced during the 1×EXT and 3×EXT treatments (P < 0.01). An additional experiment was conducted to determine the effect of time on blood flow and VFA flux because buffer sequence could not be randomized. Time either increased (P = 0.05) or did not affect blood flow (P = 0.18) or VFA flux (P > 0.80), indicating that observed differences are due to the presence of ergot alkaloids in the rumen. A decrease in VFA absorption could contribute to the signs of fescue toxicosis including depressed growth and performance.