Degradation of Ergoline Alkaloids during In Vitro Ruminal Digestion of Tall Fescue Forage

Abstract

Tall fescue (Festuca arundinacea Schreb.) is an important forage grass in the USA, but most is infected with an endophytic fungus, Acremonium coenophialum Morgan‐Jones & W. Gams. The endophyte mediates production of ergopeptine alkaloids, the compounds implicated in fescue toxicosis of cattle (Bos taurus L.). Alteration of pyrrolizidine alkaloids has been demonstrated in the rumen, but the fate of ergoline alkaloids associated with tall fescue remains to be investigated. This experiment was performed to gain information as to the extent and rate of in vitro ruminal degradation of such alkaloids. Endogenous ergovaline (EV) and exogenous ergonovine (EN) were measured in fractions of the digest using HPLC. Soluble (SOL) and insoluble (INSOL) fractions before (0 h) and after 6, 12, 24, 48 h of in vitro tall rescue forage digestion were lyophilized, extracted, and assayed. Most (> 72%) of the EN measured in the digest was found in the SOL fraction, where it declined in concentration to 35% of the initial 1105 µg kg−1 in 24 h, but decreased little thereafter. Ergonovine in the INSOL fraction declined linearly throughout the incubation period, such that only 5% of the initial concentration was present after 48 h. Endogenous EV concentration in the SOL fraction declined linearly from 272 to 32 µg kg−1 during the 48‐h incubation. The concentration of EV in the remaining dry weight of the INSOL fraction exhibited an apparent increase, possibly because EV was sequestered in fungal or plant cell walls. Thus, both alkaloids studied were susceptible to ruminal degradation when exposed to the liquid phase. Application of these results depends on the location of the primary site of ergoline alkaloid absorption.