Biological Significance of Reed Canarygrass Alkaloids and Associated Palatability Variation to Grazing Sheep and Cattle¹

Abstract

Total basic alkaloid concentration of reed canarygrass (Phalaris arundinacea L.) is negatively correlated with palatability (selection when a choice is offered) of the grass to ruminant animals. The significance of these alkaloids to ruminants not offered a choice of pasture forage remained unknown. Our objectives were to determine whether alkaloid concentration and alkaloid type differences among reed canarygrass genotypes affect animal performance, grass intake, and health of grazing sheep and cattle. Replicated pastures representing two primary alkaloid types (gramine vs. tryptamine‐carboline) and two alkaloid concentrations were primarily established from eight clones of reed canarygrass. During 1973 and 1974, these pastures were grazed by lambs and during 1975, by steers. Total alkaloid concentration of the grass was highly negatively associated with average daily gains by lambs and steers (r= —0.91, —0.90, and —0.91 for 1973, 1974, and 1975, respectively). Alkaloid concentration was highly negatively correlated with an estimate of voluntary intake (r = −0.85) by lambs not offered a choice of reed canarygrass genotypes, but alkaloid concentration was not usually overtly associated with voluntary intake by steers. Animals had more diarrhea when grazing high‐alkaloid plants and when grazing tryptamine‐carboline‐containing compared to gramine‐containing plants. This physiological upset may have been a major contributor to reduced animal gains. Breeding or managing reed canarygrass cultivars for lower alkaloid concentration per se, and breeding for tryptamine‐carboline‐free (gramine‐containing) cultivars, should provide pasture that has improved animal performance potential. “Phalaris staggers” or “sudden death” were not incited in sheep or cattle grazing exclusively reed canarygrass that had very high indole alkaloid concentrations. This indicated that these disorders, thought to be caused by indole alkaloids in animals grazing Phalaris species, are very likely not caused by indole alkaloids alone. We have conclusively demonstrated that palatability differences and their associated alkaloid concentration differences among reed canarygrass genotypes have a substantial biological significance for grazing lambs and steers.

Anti-quality factors associated with alkaloids in eastern temperate pasture

“…Total indole alkaloid concentration (gramine, tryptamines and carbolines) was inversely correlated with weight gains in lambs and steers (Marten et al 1976). Marten et al (1981) indicated that a total alkaloid concentration greater than 2.0 mg/g dry weight of forage reduces animal gains.…”

“…These alkaloids are concentrated in the immature leaf sheaths and blades (Woods et al 1979). They reduce palatability of the grass, and thus serve as animal deterrants to prevent overgrazing (Marten et al 1976). The tryptamine and carboline alkaloids create digestive disorders resulting in a greater incidence of diarrhea in sheep compared to either the hordenine or gramine alkaloids (Marten et al 1981).…”

“…Hordenine and gramine alkaloids simply reduce average daily gains. Hence, there are metabolic differences in modes of action; however, forage refusal correlates better with total alkaloid concentration than with the individual alkaloid classes (Marten et al 1976). The alkaloids in reed canarygrass are under simple genetic control and are highly heritable (Marum et al 1979, Woods et al 1979.…”

Prospects for improving the nutritive value of temperate, perennial pasture grasses

“…Seasonal changes in palatability occur in P. aquatica and P. arundinacea (Oram et al 1985). Genetic variability in palatability has been established for P. arundinacea (Marten et al 1976). In Eragrostis curvula (weeping lovegrass), there are palatability differences between different lines (Leigh 1961;Voight et al 1970) but the reasons are not clear.…”

Effects of Selected Reed Canary Grass Alkaloids on in Vitro Digestibility

“…Enatic seed yields (Vose 1959) ;Marten 1973;Gander et al 1976). Simons and Marten (19'71) reported highly negative correlations between palatability and total alkaloid content, while Marten et al (1976) In studies on tall fescue (Festuca arundinacea Schreb. ), Bush et al (1970Bush et al ( ,1972 found that pedoline, an alkaloid of this (Coulman et al 1976).…”