This study was conducted to determine the effects of heat treated-soybean meal, fish meal, meat meal, and an equal blend of fish and meat meal as rumen-ungradable protein (RUP) sources on productive performance, nutrient digestibility, N-utilization efficiency, and blood metabolites in high-producing Holstein dairy cows. Twelve lactating Holstein cows (DIM = 89 ± 11; mean ± SD) were used in a replicated 4 × 4 Latin square design receiving four diets formulated with amounts (DM basis): (1) 3.1% heat treated-soybean meal (T-SBM), (2) 2.5% fish meal (FM), (3) 3.0% meat and bone meal (MM), and (4) an equal blend of 1.4% FM plus 1.4% MM (FMM), as dietary RUP sources. The crude protein concentration was kept constant across the treatments (16.7% of DM). The duration of each experimental period was 21 d with 15 d devoted to dietary adaptation and 6 d to data collection. Dry matter intake (24.2 kg/d), actual milk (41.8 kg/d), 4% fat-corrected milk yield (35.6 kg/d), milk composition (Fat = 3.03%, Protein = 2.90%), and blood metabolites were not affected by treatments. Apparent N efficiency (29.5%) was similar across the diets. Based on our results, T-SBM, FM, MM, and mixed of FM and MM had a similar effect on productivity and N-utilization efficiency in lactating dairy cows. Based on the income over feed cost (IOFC), under our experimental conditions, use of the meat meal as a source of dietary RUP can be recommended as a feeding strategy for feed to lactating cows receiving high-concentrate diets.