Browsing Journal of Range Management, Volume 54, Number 4 (July 2001) by Subjects
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Alkaloids as anti-quality factors in plants on western U.S. rangelandsAlkaloids constitute the largest class of plant secondary compounds, occurring in 20 to 30% of perennial herbaceous species in North America. Alkaloid-containing plants are of interest, first because alkaloids often have pronounced physiological reactions when ingested by livestock, and second because alkaloids have distinctive taste characteristics. Thus, alkaloids may kill, injure, or reduce productivity of livestock, and have the potential to directly or indirectly alter diet selection. We review 7 major categories of toxic alkaloids, including pyrrolizidine (e.g., Senecio), quinolizidine (e.g., Lupinus), indolizidine (e.g., Astragalus), diterpenoid (e.g., Delphinium), piperidine (e.g., Conium), pyridine (e.g., Nicotiana), and steroidal (Veratrum-type) alkaloids. Clinically, effects on animal production vary from minimal feed refusal to abortion, birth defects, wasting diseases, agalactia, and death. There are marked species differences in reactions to alkaloids. This has been attributed to rumen metabolism, alkaloid absorption, metabolism, excretion or directly related to their affinity to target tissues such as binding at receptor sites. In spite of alkaloids reputed bitter taste to livestock, some alkaloid-containing plant genera (e.g., Delphinium, Veratrum, Astragalus, Oxytropis, and Lupinus) are often readily ingested by livestock. Management schemes to prevent losses are usually based on recognizing the particular toxic plant, knowing the mechanism of toxicity, and understanding the temporal dynamics of plant alkaloid concentration and consumption by livestock. Once these aforementioned aspects are understood, losses may be reduced by maintaining optimal forage conditions, adjusting grazing pressure and timing of grazing, aversive conditioning, strategic supplementation, changing livestock species, and herbicidal control.
Anti-quality components in forage: Overview, significance, and economic impactAlthough recognized in importance from the dawn of history, forages have too often been underestimated and undervalued perhaps in part because animal performance has frequently failed to reflect apparent forage quality. Anti-quality components, diverse impediments to quality, have evolved as structural components and as secondary metabolites. They include mineral imbalances or can be related to the presence of insects and diseases. Animal behavior and adaptation are increasingly recognized as important aspects of anti-quality factors. An anti-quality component may reduce dry matter intake, dry matter digestibility, or result in nutritional imbalances in animals. They can act as a direct poison compromising vital systems, result in abnormal reproduction, endocrine function, and genetic aberrations, trigger undesirable behavior responses, or suppress immune function leading to increased morbidity and mortality. The economic impact of anti-quality factors on individual herds can be devastating but definable. Broadscale economic impacts of anti-quality factors are far more difficult to estimate. A loss of 0.22 kg/day in potential gain of stocker cattle due to anti-quality factors during a 166-day grazing season translates into a loss of about 55/steer at 1.45/kg or over 2 billion annually when applied to the U.S stocker cattle. Economic losses to tall fescue (Festuca arundinacea Schreb.) toxicosis in the U.S. beef industry are probably underestimated at 600 million annually. Reproductive and death losses of livestock due to poisonous plants have been estimated at 340 million in the 17 western states alone. These examples of economic losses due to anti-quality factors may be upper bounds of actual losses but even if a small proportion of the expected losses were eliminated through research, the potential payoff would be extremely high.