|FOOTE, ANDREW - University Of Kentucky|
|KRISTENSEN, NIELS - Southern Cattle|
|KIM, DOHYUNG - University Of Kentucky|
|KOONTZ, ANNE - University Of Kentucky|
|MCLEOD, KYLE - University Of Kentucky|
|BUSH, LOWELL - University Of Kentucky|
|SCHRICK, F - University Of Tennessee|
|HARMON, DAVID - University Of Kentucky|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2013
Publication Date: 8/29/2013
Citation: Foote, A.P., Kristensen, N.B., Klotz, J.L., Kim, D., Koontz, A.F., Mcleod, K.R., Bush, L.P., Schrick, F.N., Harmon, D.L. 2013. Ergot alkaloids from endophyte-infected tall fescue decrease reticulo-ruminal epithelial blood flow and volatile fatty acid absorption from a washed reticulorumen. Journal of Animal Science. 91:5366-5378.
Interpretive Summary: The effect of ergot alkaloids on gut physiology has not been extensively studied. Feeding common toxic tall fescue hay infected with the fungal endophyte Neotyphodium coenophialum has been shown to have little effect on portal nutrient flux. The purpose of this experiment was to determine the effect of ergot alkaloids on reticuloruminal epithelial blood flow and VFA absorption from the washed reticulorumen of steers receiving endophyte-infected or endophyte-free tall fescue seed in the presence of increasing levels of ergot alkaloids in steers housed at thermoneutral and heat stress conditions. Ergot alkaloids from tall fescue seed and a tall fescue seed extract induced a large reduction in blood flow to the absorptive surface of the reticulorumen of cattle housed in thermoneutral and heat stress conditions. Additionally, ergot alkaloids caused a reduction in VFA absorption from a washed reticulorumen that is likely related to the reduction in blood flow to the absorptive surface of the foregut. The depression of nutrient absorption related to toxic tall fescue exposure could contribute to the common symptoms of fescue toxicosis such as decreased growth and performance.
Technical Abstract: 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 tall fescue seed (E+; 0.015 mg ergovaline•kg BW-1•d-1) or endophyte-free tall fescue seed (E-) via rumen cannula 2× daily for 7 d at thermoneutral (TN; 22 °C) and heat stress (HS; 30°C) conditions in an incomplete crossover. On d 8 the rumen was emptied and rinsed with water and saline. A buffer containing volatile fatty acids (VFA) was incubated in the following sequence: control (CON), 15 µg ergovaline/kg BW (1×EXT), and 45 µg ergovaline/kg BW (3×EXT). Ergovaline in the buffer was supplied as a tall fescue seed extract solubilized in 80% methanol. For each buffer treatment there were two 30-min incubations; a 30 min incubation of a treatment buffer with no sampling followed by removal of the buffer and incubation of an identical sampling buffer with the addition of Cr-EDTA and D2O. Epithelial blood flow was estimated as ruminal clearance of D2O corrected for influx of physiological water and liquid outflow. Feed intake decreased with dosing E+ at HS but not at TN (P=0.0182). Dosing E+ seed decreased serum prolactin (P=0.0049) at TN. At HS prolactin decreased in both E+ and E- steers over the 8 d experiment (P<0.0001) but there was no difference in E+ and E- steers (P=0.3303). There was a seed treatment × buffer treatment interaction at TN (P=0.0376) 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 the 1×EXT and 3×EXT. Inclusion of the seed extract in the buffer caused at least a 50% reduction in epithelial blood flow at TN (P=0.00376) but there was no difference between 1×EXT and 3×EXT. There was a seed treatment × buffer treatment interaction at HS (P=0.0054) indicating that the reduction of blood flow induced by incubating the extract was larger for steers receiving E- seed than E+ seed. VFA 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 did not affect blood flow or VFA flux, indicating that observed differences are due to the presence of ergot alkaloids in the rumen. A decrease in VFA absorption could contribute to the symptoms of fescue toxicosis including depressed growth and performance.