Influence of native shrubs on nutritional status of goats: nitrogen retention

Abstract

In vivo digestibility trials were conducted to evaluate the influence of shrubs containing low and high levels of soluble phenolic/-tannins on digestibility and nitrogen retention by Angora goats. Each of 6 shrubs and alfalfa hay (Medicago sativa L.) were fed to goats at 30% (dry matter basis) of the diet in a barley straw-prairie hay mixture. The mixture was regulated so that all diets contained about 8% crude protein. High soluble phenolic shrubs used included big sagebrush (Artemisia tridentata Nutt. ssp. tridentata), gray oak (Quercus grisea Liebm.), true mountain mahogany (Cercocarpus montanus Raf.), and one-seed juniper (Juniperus monosperma [Engelm.] Sarg). Low-soluble phenolic species included common winterfat (Ceratoides lanata [Pursh.], J.T. Howell), fourwing saltbush (Atriplex canescens [Pursh.], Nutt.), and alfalfa. Nitrogen digestibilities of winterfat, gray oak, mountain mahogany and one-seed juniper diets were less (P<.05) than the alfalfa controls, but big sagebrush did not differ (P>.05) compared with the alfalfa control. Retained nitrogen (g/d) differed (P<.05) only among alfalfa, juniper, and mountain mahogany diets. Goats fed juniper had greater (P<0.05) retained nitrogen than the alfalfa control. Shrubs high in soluble phenolics, with the exception of big sagebrush, had elevated fecal nitrogen losses, but reduced urinary nitrogen losses compared with the alfalfa control. Forage organic matter intake (% body weight) and nitrogen intake (g/d) were correlated more highly with nitrogen retention than dietary crude protein (%) or digestible protein (%). Present data indicate that protein found in palatable native shrubs is assimilated with similar efficiency to that in alfalfa hay if these shrubs are consumed at moderate levels.