Sl. Kronberg et Jw. Walker, RUMINAL METABOLISM OF LEAFY SPURGE IN SHEEP AND GOATS - A POTENTIAL EXPLANATION FOR DIFFERENTIAL FORAGING ON SPURGE BY SHEEP, GOATS, AND CATTLE, Journal of chemical ecology, 19(9), 1993, pp. 2007-2017
Leafy spurge (Euphorbia esula) is an introduced forb that is invading
western rangelands. Goats (Capra hircus) readily graze the plant, but
cattle (Bos tarus) generally and sheep (Ovis aries) locally appear to
develop conditioned flavor aversions to leafy spurge. They either avoi
d the plant entirely or graze it reluctantly. We hypothesized that: (1
) a diterpene diester that can occur in leafy spurge was an aversive a
gent, and (2) diet selection differences among ruminant species may be
partly a function of differential ruminal metabolism of aversive phyt
ochemicals, and further that cattle and sheep may be reluctant to graz
e leafy spurge because their ruminal microbes do not metabolize certai
n leafy spurge chemicals as do ruminal microbes in goats. Sheep did no
t develop an aversion to a novel food when its consumption was followe
d by an intravenous injection of ingenol 3,20-dibenzoate (P = 0.34). S
heep did develop an aversion to a novel food when its intake was follo
wed by a dose of leafy spurge fermented with sheep ruminal digesta, bu
t not when followed by a dose of leafy spurge fermented with goat rumi
nal digesta (P = 0.03). This suggests that goat ruminal microbes may m
odify leafy spurge such that it does not elicit an aversion in sheep.