Macronutrients and additives have been used to suppress or promote intake of upland tannin-containing browse species by livestock, but to our knowledge this technique has not been applied to sheep that feed on tannin-containing species in riparian areas. The objective of this study was to determine the effect of four supplement regimes on coyote willow (Salix exigua) intake by sheep during the dormant and growing seasons. Twelve Western White Face lambs (48 ± 4.5 kg) were placed in individual pens and assigned to one of four treatments which consisted of a basal diet of sudangrass and supplements predicted to either suppress (whole corn or quebracho tannin) or promote (cottonseed meal or polyethylene glycol, PEG) willow intake. Each of the four supplements was tested with dormant and growing willow in a Latin rectangle design with 3 periods and 6 lambs per group. Basal diet (sudangrass) intake was affected by neither promoter nor suppressor treatments in either season. Cottonseed meal effectively promoted intake of willow compared to the control and PEG treatments (P< 0.05) in the dormant season. No difference was detected between the control, quebracho tannin, and whole corn treatments, although the latter tended to depress dormant willow intake of lambs. None of the treatments altered intake of coyote willow in the growing season trials. Protein and possibly corn-based supplements may be effective tools to manipulate sheep browsing levels of Salix exigua but need to be tested in a field setting before management strategies with supplementation can be applied.