FORB AND SHRUB INFLUENCES ON STEER NITROGEN-RETENTION

Two experiments with steers were conducted to evaluate the influence o f native forbs and shrubs on nitrogen utilization by cattle. Diets in Exp. 1 were blue grama (Bouteloua gracilis [H.B.K.]) (BG), BG plus 23% alfalfa (Medicago sativa) hay (ALF), BG plus 42% forbs and BG plus 41 % shrubs. Diets in Exp. 2 included barley (Hordeum vulgare L.) straw, and straw plus either 42% ALF, 63% forbs, or 62% shrubs. Forbs used in our study were scarlet globemallow (Sphaerakcea coccinea Nutt.) and l eatherleaf croton (Croton pottsii Lam.). Shrubs included fourwing salt bush (Atriplex canescens [Pursh.]) and mountain mahogany (Cercocarpus montanus Raf.) Forb and shrub mixtures were 50:50 of each species. Blu e grama and straw basal diets contained 7.6 and 3.5% CP, respectively. Diets containing ALF, forbs, and shrubs were isonitrogenous (10.5% CP ) in both experiments. In Exp. 1, no differences (P > .10) were observ ed among treatments for N retention (g/d). In Exp. 2, N retention was least (P < .05) for the straw diet, greatest for the ALF and shrub die ts (P > .05), and intermediate for the forb diet. Inclusion of forbs o r shrubs with low-quality forage diets was, in most instances, compara ble to inclusion of ALF. Our results indicate that maintaining palatab le forbs and shrubs on rangelands should reduce the need to supply cat tle with protein during periods when grasses are dormant.