A mixture of cool-season grasses brought the most weight gain in a University of Wyoming irrigated pasture study. But fertilizer costs were higher than for the other forages tested.

Wyoming agronomists grazed yearling steers on grass, alfalfa or cicer milkvetch from May to September. Per-acre gains were 862 lbs for the grasses, 634 lbs for alfalfa and 503 lbs for cicer milkvetch.

The grasses were more resistant to trampling damage, but significant amounts of nitrogen were needed for high yields. The nitrogen also increases the risk that nitrates will leach into groundwater, say the agronomists.

Legumes appear more environmentally friendly, they say. But alfalfa is more susceptible to trampling damage than grasses, and preventing bloat involves some cost. Cicer milkvetch doesn’t cause bloat, but it’s slow to establish and produced the least amount of gain in this study.

"Various tradeoffs are involved with each forage type," say the researchers.