Cattle prefer endophyte-free robust needlegrass

Abstract

Robust needlegrass (Achnatherum robustum [Vasey] Barkw. = Stipa robusta [Vasey] Scribn.) is a high-biomass rangeland species that is adapted to warmer temperatures and matures later than most cool-season grasses. However, it has been associated with negative animal effects including avoidance. We compared populations of Neotyphodium and P-endophyte-infected endophyte-infected (E+) and endophyte-free (E-) robust needle-grass for animal preference. Leaf blades were fed to yearling heifers in 3 trials of 8-min cafeteria sessions for 4 to 5 days each. Trial 1 (27-30 May) compared E+, E-, basin wildrye (Leymus cinereus [Scribn. Merr.] A. Löve), and tall wheatgrass (Thinopyrum ponticum [Podp.] Barkw. D.R. Dewey). Basin wildrye consumption (425 g) did not differ from tall wheatgrass (342 g), but basin wildrye consumption exceeded E- (258 g), which in turn exceeded E+ (117 g) (16 animal-sessions). Basin wildrye was dropped from Trial 2 because its consumption exceeded that of both E- and E+. In Trial 2 (1-5 June), consumption of E-, E+, and tall wheatgrass did not differ. Tall wheatgrass was dropped from Trial 3 to allow direct comparison of E- and E+. In Trial 3 (13-17 July), consumption of E- (585 g) exceeded E+ (145 g) (15 animal-sessions). In Trial 3, animals often rejected E+ forage before tasting. Discrimination against E+ was greater at the end of Trial 3 than at the beginning. The reputation of robust needlegrass for animal avoidance may be more related to its endophyte infection status than to the grass itself. Differences in forage-quality parameters were not large enough to account for the observed differences in preference. Ergot and loline alkaloids were not found in either E- or E+, therefore they cannot be responsible for the observed avoidance of E+. Non-trace amounts of ergot alkaloids were found only in seed collected in the Sacramento Mountains of New Mexico and not at other locations in New Mexico, Arizona, or Colorado.