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Fifty- eight Holstein steers with an initial body weight of 469 lb were fed 1 of 5 dietary treatments containing different rumen undegradable protein (RUP) sources: control with no supplemental protein, field peas, field peas plus fish meal, soybean meal, and SoyPass, a treated soybean meal high in RUP. These protein sources replaced corn in a base diet of 65% dry rolled corn, 30% alfalfa haylage, and 5% supplement in order to balance for metabolizable protein (MP). Th e objective of this study was to compare how rumen undegradable protein sources that can be found in organic production systems affect the growth and performance of lightweight Holstein steers. Using supplemental RUP to balance for MP improved F:G by 25% in the first feeding phase regardless of RUP source. Over the feeding period, steers in all treatments gained similarly and had similar final body weight, but steers fed field peas plus fish meal tended to be more efficient than other calves. Supplementing field peas or field peas and fish meal did not result in an increase in cost of gain over calves not fed supplemental RUP. Supplemental RUP increased live weight gained by up to 14.2%. These data indicate that using feedstuff s that can be found in organic production systems to supplement RUP can result in improved F:G without increasing cost of gain.