Structural 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.

Effect of water on retention time and food consumption in deer mice. Can. J. Zool. 72: 171 1 -1714. Experiments were conducted to assess the effect of water on food consumption and retention time in deer mice (Peromyscus maniculatus). We tested whether increased intake of water, preformed in food or free drinking water, affects mean retention time and consumption of food. Mean retention times for diets of sunflower seeds (Helianthus annuus), commercial rat chow, and insect-seed mixtures were estimated by using 2-mm red thread markers. For all diets, mean retention time and food intake were negatively and positively correlated, respectively, with water intake. Mean retention times decreased more rapidly with increased water content for sunflower seeds than for rat chow, suggesting that food type also may be important. Granivorous rodents may consume wet food items during periods of low water availability to increase energy intake rather than to satisfy water requirements.REID, E.D., et BROOKS, R.J. 1994. Effect of water on retention time and food consumption in deer mice. Can. J. Zool. 72 : 1711-1714. Des exp6riences ont permis de mesurer l'effet de l'eau sur la consommation et la rktention de nourriture chez la Souris a pattes blanches (Peromyscus maniculatus). Nous avons tent6 de voir si l'augmentation de la consommation d'eau, sous forme libre ou prCformCe (dans la nourriture), affecte la consommation de nourriture et la durCe moyenne de la rCtention. La durCe moyenne de rCtention a Ct C CvaluCe au moyen de marqueurs constituks de fils 'rouges de 2 mm aprks des repas de graines de tournesol (Helianthus annuus), de moulCe commerciale pour les rats et de mklanges d'insectes et de graines. Dans tous les cas, la durCe moyenne de la rCtention Ctait en corrklation nkgative avec la consommation d'eau et la consommation de nourriture Ctait en corrklation positive avec la consommation d'eau. La durCe moyenne de rCtention diminuait plus rapidement en fonction de l'augmentation de la consommation d'eau lorsqu'il s'agissait de regimes de graines de tournesol que lorsqu'il s'agissait de moulCe a rat, ce qui semble indiquer que le type de nourriture a sans doute aussi son importance. Si les rongeurs granivores consomment de la nourriture humide au cours des pCriodes plus skches, il faut peut-&re voir la une stratCgie propre a augmenter la consommation d'Cnergie plut6t qu'un moyen de satisfaire des besoins en eau.[Traduit par la RCdaction]