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ARS Home » Midwest Area » Lexington, Kentucky » Forage-animal Production Research » Research » Publications at this Location » Publication #310312
Title: Forage nutritive value and steer responses to grazing intensity and seed-head suppression of endophyte-free tall fescue in mixed pastures

Author
item GOFF, B - University Of Kentucky
item Aiken, Glen
item WITT, W - University Of Kentucky
item BURCH, P - University Of Kentucky
item SCHRICK, F - University Of Tennessee

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2015
Publication Date: 4/1/2015
Citation: Goff, B.M., Aiken, G.E., Witt, W.W., Burch, P.L., Schrick, F.N. 2015. Forage nutritive value and steer responses to grazing intensity and seed-head suppression of endophyte-free tall fescue in mixed pastures. Professional Animal Scientist. 31(2):120-129. DOI: 10.15232/pas.2014-01366.

Interpretive Summary: Tall fescue is the predominant cool-season perennial grass used for forage in the humid east. Tall fescue is persistent and productive, but cattle production and thriftiness is low because of toxic ergot alkaloids produced by a fungal endophyte that infects most plants of tall fescue. Cattle that consume endophyte-infected tall fescue can undergo a toxicosis that causes cattle to exhibit poor weight gain, rough hair coats during the summer months, and elevated core body temperatures. Seed heads contain the highest concentration of ergot alkaloids; unfortunately, cattle readily consume the highly toxic seed heads of tall fescue. Seed heads can be removed by mowing or by application of a herbicide that contains the active ingredient, metsulfuran. Chemical seed head suppression has shown to increase average daily gain of steers and mitigate signs of fescue toxicosis, but it has not been determined if the increase in weight gain was due to alleviation of toxic seed heads or by enhancement of nutritive values by maintaining the fescue in vegetative stage of growth. Results of a grazing experiment with endophyte-free tall fescue showed a boost in steer ADG that was approximately half of what was determined with endophyte-infected tall fescue. Enhancement of fescue quality through suppression of lower quality reproductive tissues will benefit calf performance, but the alleviation of toxic seed heads from endophyte-infected tall fescue will also influence on steer performance. This research provides a useful management option for improving cattle performance in non-toxic tall fescue pastures, but also provides an indication of the positive benefits of alleviating toxic seed heads from toxic tall fescue pastures.

Technical Abstract: A 2-yr grazing experiment was conducted with 8- to 10-mo old steers on pastures of endophyte-free tall fescue (Lolium arundinaceum) in mixture with other grasses to assess the effect of seed head suppression (SHS) of fescue on steer performance and forage nutritive values. With and without SHS were combined with light or moderate grazing intensities for assignment to twelve, 1.0.-ha pastures of the grass mixtures as a RCBD with three replications. Steer ADG was measured, and crude protein (CP) and in vitro DM digestibility (IVDMD) of available forage and leaf blade and sheaths of fescue tillers were monitored. Averaged over grazing intensities, ASG was 16% greater (P < 0.05) with SHS; however, a lower (P < 0.001) pasture carrying capacity with SHS resulted in a tendency of greater (P = 0.068) BW gain per ha without SHS. Crude protein of available forage was consistently greater (P < 0.01) with SHS across all dates, while IVDMD was consistently greater (P < 0.01) with SHS in the late grazing season. Crude protein in leaf blades and sheaths of vegetative tillers with SHS were consistently greater (P < 0.01) than vegetative tillers without SHS. In vitro DMD of blades and sheaths was similar (P > 0.18) between suppressed and unsuppressed vegetative tillers, and both had greater (P < 0.05) IVDMD than reproductive tillers over most dates. Results showed SHS of fescue to improve steer ADG by increasing CP in vegetative tissues and improving digestibility of available forage by alleviating lower quality, reproductive tillers.