There is a need to design intensive cropping systems that can reap multiple benefits from annual forages including animal feed, soil fertility and weed control. Considering pea/oat (Pisum sativum cv. 40–10/Avena sativa cv. Legget) as a standard green manure, this study investigated the productivity, weed competitiveness, utilization and nitrogen (N) benefit from grazed and ungrazed green manures to spring wheat (Triticum aestivum cv. Waskada) and fall rye (Secale cereale cv. Hazlet). A set of 3-year experiments was carried out in Carman, Manitoba, Canada in 2009, and was repeated in 2010 and 2011. Green manures were grazed by 2–3 ewes and 2–5 lambs for 24 h (1111–1667 sheep days per ha). Averaged over experiments pea/oat mix, hairy vetch (Vicia villosa L.) and sweetclover (Melilotus officinalis cv. Norgold) above-ground dry matter (DM) production were 5036, 5032 and 4064 kg ha−1, respectively. Lentil (Lens culinaris cv. Indianhead), a mixture of seven species and soybean (Glycine max cv. Prudence) produced the least amount of DM over 3 years; 3589, 3551, 3174 kg ha−1, respectively. Pea/oat and hairy vetch were the most weed-competitive species and, averaged over 3 years, contained less than 15% weed DM. Utilization of green manures by grazing animals varied little among species across years and ranged from 28 to 86% for individual species and years. When combined across experiments grazing increased N availability to the wheat crop. The grazing effect was significant for wheat DM production, N uptake and grain N, but not significant for yield across experiments. Averaged over 3 years, wheat took up 107 kg N ha−1 from grazed plots versus 98 kg N ha−1 from ungrazed plots. A significant species×management interaction for total (wheat+fall rye) N uptake in 2009 indicated that increasing the proportion of legumes in the green manure increased N benefit from grazing. Fall rye productivity was not affected by grazing. We recommend pea/oat and hairy vetch as two green manure species to enhance the overall system performance to achieve high level of DM production, good weed competition, utilization by sheep and provision of N benefit to the following wheat and fall rye crops.