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Two experiments with pregnant heifers grazing winter range investigated effects of supplementation to meet metabolizable protein versus CP requirements. Supplements were fed from October to February, and hay was fed in January and February of the second experiment. Supplementation to meet metabolizable protein requirements decreased weight loss in one experiment. Winter hay feeding reduced weight loss and body condition loss compared to no hay feeding. Forage intake declined from 2.1% of body weight in November to 1.3% in February. Metabolizable protein was deficient when animals were supplemented to meet CP requirements. Supplementation to meet metabolizable protein requirements may improve performance when energy intake is not deficient.