UV-B effects on the nutritional chemistry of plants and the responses of a mammalian herbivore.

Stratospheric ozone depletion has caused ground-level ultraviolet-B (UV-B) radiation to rise in temperate latitudes of both hemispheres. Because the effects of enhanced UV-B radiation on the nutrition of food consumed by mammalian herbivores are unknown, we measured nutritional and chemical constituents of 18 forages and related changes to in vitro dry matter digestibility. We also measured intake and in vivo digestibility of Pacific willow (Salix lasiandra) and alfalfa (Medicago sativa L.) by blue duikers (Cephalophus monticola). Forages were irradiated for 3 months with ambient (1x) or supplemental (1.6 x) UV-B radiation representing a 15% ozone depletion for Pullman, Washington, USA. Enhanced UV-B radiation had minimal and inconsistent effects on the nutritional content, in vitro dry matter digestibility, and protein-binding capacity of forages. However, flavonoid compounds increased in seven of the 13 forbs and woody dicots that were evaluated. Flavonoids were found to decrease only in yarrow (Achillea millefolium). When offered simultaneously, blue duikers preferred 1x and 1.6 x UV-B irradiated plants of alfalfa equally, but ate 26% less willow grown under 1.6 x UV-B radiation. However, when fed to duikers in separate feeding experiments, total dry matter intake and in vivo digestibility of dry matter, fiber, protein, and apparent energy did not differ between alfalfa and willow grown under 1x and 1.6 x UV-B radiation. We conclude that expected increases in UV-B radiation from ozone depletion would have minimal effects on intake and digestion of ruminant herbivores.