Browsing Journal of Range Management, Volume 54, Number 4 (July 2001) by Subjects
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Herbivore response to anti-quality factors in foragesPlants possess a wide variety of compounds and growth forms that are termed "anti-quality" factors because they reduce forage value and deter grazing. Anti-quality attributes can reduce a plant's digestible nutrients and energy or yield toxic effects. Herbivores possess several adaptive mechanisms to lessen the impacts of anti-quality factors. First, herbivores graze selectively to limit consumption of potentially harmful plant compounds. Grazing animals rely on a sophisticated system to detect plant nutritional value or toxicity by relating the flavor of a plant to its positive or negative digestive consequences. Diet selection skills are enhanced by adaptive intake patterns that limit the deleterious effects of plant allelochemicals; these include cautious sampling of sample new foods, consuming a varied diet, and eating plants in a cyclic, intermittent, or carefully regulated fashion. Second, grazing animals possess internal systems that detoxify or tolerate ingested phytotoxins. Animals may eject toxic plant material quickly after ingestion, secrete substances in the mouth or gut to render allelochemicals inert, rely on rumen microbes to detoxify allelochemicals, absorb phytochemicals from the gut and detoxified them in body tissues, or develop a tolerance to the toxic effects of plant allelochemicals. Understanding the behavioral and metabolic abilities of herbivores suggests several livestock management practices to help animals contend with plant anti-quality characteristics. These practices include offering animals proper early life experiences, selecting the appropriate livestock species and individuals, breeding animals with desired attributes, and offering nutritional or pharmaceutical products to aid in digestion and detoxification.
Structural anti-quality characteristics of range and pasture plantsStructural anti-quality characteristics are physical plant traits that reduce the performance and productivity of herbivores and quality of their agricultural products. Most structural anti-quality characteristics of plants affect the rate at which herbivores gather and ingest forages, reducing the total amount of food obtained or increasing the time necessary to obtain food. Structural anti-quality can substantially influence searching time (e.g., plant crypticity, distribution), cropping time (e.g., plant fibrousness, tensile and shear strength), and bite size (e.g., plant canopy structure, spinescence). Plant structural characteristics can also reduce digestion (e.g., silica), cause injury (e.g., spines, awns, burrs, calluses), or reduce the quality of animal products, such as wool (e.g., propagules). The effects of structural antiquality characteristics depend on the morphology of the herbivore, especially its size, the morphology of the focal plant, and their context within the habitat. Integrated grazing management plans should consider options to reduce the negative effects of structural anti-quality. Carefully selecting appropriate livestock species with previous experience, and the appropriate season of grazing can minimize anti-quality on rangelands. Because structural anti-quality may actually promote sustainability of grazing systems by preventing severe defoliation, or by providing refuges for highly desirable forages, it may not be desirable to completely counteract their effects.