Ja. Pfister et al., INFLUENCE OF ALKALOID CONCENTRATION ON ACCEPTABILITY OF TALL LARKSPUR(DELPHINIUM SPP) TO CATTLE AND SHEEP, Journal of chemical ecology, 22(6), 1996, pp. 1147-1168
Tall larkspur (Delphinium spp.) is a serious toxic plant problem on we
stern U.S. ranges, The major toxins in tall larkspur are methyllycacon
itine (MLA) and 14-deacetylnudicauline (14-DAN); the sum of both is te
rmed the toxic alkaloid concentration. Toxic alkaloids comprise about
20-50% of the total alkaloid concentration in tall larkspur. Toxic and
total alkaloid concentration generally declines with maturity, wherea
s cattle and sheep consumption of larkspur typically increases with pl
ant maturity. We hypothesized that cattle and sheep consumption of tal
l larkspur was negatively related to higher concentrations of total or
toxic alkaloid. We compared consumption of several collections of dri
ed, ground larkspur and fresh larkspur in a series of trials. In anoth
er trial, a crude alkaloid fraction was extracted with ethanol, added
to alfalfa hay, and consumption compared to untreated alfalfa hay, alc
ohol-treated hay, and the essentially alkaloid-free plant residue. In
all cases we correlated amounts eaten with total and toxic alkaloid co
ncentration. A grazing trial was also conducted to relate larkspur con
sumption over time to alkaloid concentrations. Total alkaloid concentr
ations in dried, whole-plant collections ranged from 9.3 to 38.8 mg/g
of dry weight, whereas toxic alkaloid concentrations varied from 0.0 t
o 7.1 mg/g. In one pen trial, cattle preferred a larkspur collection (
P < 0.01) that contained no toxic alkaloids but had a high total alkal
oid concentration (39 mg/g). There was no correlation (P > 0.05), howe
ver, between concentrations of total or toxic alkaloids and amount of
dry plant consumed in this or any other trial. Conversely, sheep consu
mption tended to be negatively influenced by total and toxic alkaloid
concentration (P less than or equal to 0.08). In the trials with extra
ct, cattle preferred the alcohol-treated hay and rejected the alkaloid
-free residue (P < 0.01), whereas the alkaloid-treated hay was of inte
rmediate acceptability. Cattle preferred the alkaloid-treated hay over
the alkaloid-free residue, indicating that alkaloids did not deter co
nsumption. Conversely, the alkaloid-treated hay was less preferred tha
n either untreated or alcohol-treated hay, suggesting a negative effec
t on acceptability. There was no correlation between alkaloid concentr
ation and amount of treated feed eaten. In field trials, the amount of
composited, fresh leaves or flowers eaten by cattle was influenced by
plant part (P = 0.04), but was not related (P > 0.05) to alkaloid con
centration. Cattle preferred leaves over Rowers when offered individua
l plants differing in phenological stage and/or amount of shade. but a
lkaloid concentration was not related to consumption. We conclude that
knowledge of the concentration of total or toxic alkaloid in tall lar
kspur will give little or no indication of plant acceptability to catt
le. Even though accurate predictions can be made about the potential t
oxicity of larkspur based on the concentration of toxic alkaloids, pre
dictions about consumption must be based primarily on plant phenology.