Objectives were to use meta-analytic methods to determine the effects of dietary supply of MP prepartum on performance of dairy cows. The literature was systematically reviewed and 27 randomized experiments that manipulated prepartum dietary MP supply, including 125 treatment means and 1,801 cows, were included in the meta-analysis. Eight experiments with 27 treatment means reported responses for 510 nulliparous cows. Data collected included the ingredient composition and chemical analyses of prepartum diets, parity group, days on prepartum treatment, and means and respective SEM for DMI and productive responses. Diets were entered into NRC (2001) software to predict supplies metabolizable protein (MP) and metabolizable amino acids prepartum. Mixed effects meta-analysis was conducted and statistical models investigated the effects of dietary prepartum MP supply (g/d) on performance. Models included the random effect of experiment and were weighted by the inverse of SEM squared to account for the precision of each experiment. The estimated supply of MP resulted in distinct ranges in nulliparous (517 to 1,094 g/d) and parous cows (463 to 1,733 g/d); therefore, data were analyzed separately for each parity group. In nulliparous cows, increasing the prepartum MP supply linearly (P < 0.05) increased postpartum DMI (β = 0.0089 ± 0.0006; increasing MP supply from 800 to 1,000 g/d increased DMI by 1.7 kg/d), milk yield (β = 0.0058 ± 0.0023; increment = 1.1 kg/d), FCM (β = 0.0072 ± 0.0022; increment = 1.4 kg/d) fat yield (β = 0.0002 ± 0.0001; increment = 0.05 kg/d) and protein yield (β = 0.00005 ± 0.00002; increment = 0.03 kg/d). However, in parous cows, increasing prepartum MP supply had no effects on DMI, yields of milk, FCM, and milk fat, but linearly increased (P < 0.05) protein yield only in cows producing more than 36 kg/d of milk (β = 0.00006 ± 0.00002; increment by increasing MP supply from 900 to 1,200 g/d = 0.02 kg/d). Prepartum diets for nulliparous cows should supply 1,100 g of MP that was upper limit in the database, whereas minor benefits were observed of feeding parous cows more than 800 g/d MP.