Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/10/2012
Publication Date: N/A
Interpretive Summary: Tall fescue is a productive and persistent cool-season perennial grass that is the predominant grass utilized for forage in the transition zone between the temperate northeast and subtropical southeast. Unfortunately, ergot alkaloids produced by a fungal that infects most tall fescue plants can cause fescue toxicosis in cattle. Ergot alkaloids cause a constriction of blood flow to peripheral tissues to reduce the animal’s ability to regulate body temperature and they become vulnerable to both heat and cold stresses. Seed heads of tall fescue are highly concentrated with ergot alkaloids and, unfortunately, are selectively grazed by cattle; however, seed heads of tall fescue can be chemically suppressed using Chaparral herbicide (Dow AgroSciences,Indianapolis, IN). Preliminary data was generated from a pen experiment conducted with steers that previously grazed tall fescue pastures that were either with or without suppression of seed heads. Results indicated that blood flow in steers grazed on seed head suppressed pastures had more rapid recovery than those on pastures without seed head suppression. Steers on seed suppressed pastures also had post-graze body weights that were comparable to the steers that had grazed the bermudagrass control pastures. These results will be useful to cattle producers that are backgrounding beef calves on tall fescue pastures for the feedyard and need management technologies to improve weight gain and well being.
Technical Abstract: Seed heads of tall fescue can be chemically suppressed and eliminated as a source of toxic ergot alkaloids, but a reduction in alkaloid-induced vasoconstriction has not been determined in seed head suppressed tall fescue. A preliminary pen experiment was conducted with 30 steers to compare vasoconstriction of the caudal artery and post-graze performance following grazing of toxic endophyte-infected tall fescue that was with (n = 12) or without (n = 12) seed head suppression, or a bermudagrass control (n = 6). Steers were assigned to 3 pen replications after 103 days of grazing in a randomized complete block design. Cross-sectional luminal areas of the caudal artery were measured using color Doppler ultrasonography and unshrunk body weights were recorded initially and at 7-d intervals for 42 days. Luminal areas of the caudal artery in steers grazed on seed head suppressed tall fescue showed curvilinear increases over time and were similar to those in control steers by 20 days in the pens (DIP), and cross-sectional areas in steers grazed on tall fescue without suppression increased linearly over DIP and did not differ from those of control steers until 30 DIP. Steers on all treatments increased linearly over DIP, but BW of steers on seed head suppressed pastures did not differ from those of control steers over all DIP; however, BW of steers grazing pastures without seed head suppression were never statistically similar to control steers over the duration of the pen experiment even though the ADG of the fescue steers was greater than control steers. Results of these preliminary data indicate that bioaccumulation of alkaloids is reduced in steers grazing toxic endophyte-infected tall fescue, which could provide some advantage for these steers during post-graze finishing.