Besides Lys and Met, current ration-balancing programs suggest that the supply of branched-chain amino acids (BCAA; Ile, Leu, and Val) may also be limiting in dairy cows. Several studies have investigated the effects of BCAA supplementation, but results have been inconsistent. A meta-analysis was conducted to quantitatively summarize the effects of BCAA supplementation, independent of Met and Lys supplementation, in lactating dairy cows. Twenty-five observations of EAA supplementations (% of MP); milk yield (MlkY, kg/d); and milk protein (MlkP, %), fat (MlkF, %), and lactose (MlkL, %) were retrieved from 14 controlled studies with post-ruminal or jugular infusions of essential AA (EAA), all including BCAA, Met, and Lys. The effects of AA infusions on MlkY, MlkP, MlkF, and MlkL were first quantified via the mean difference (MD, MD = infusion – control), using random-effect models. Relationships between MD and changes in individual BCAA flows (% of MP) were then quantified using mixed-effect models. All analyses were conducted with a multilevel meta-analytic approach accounting for heterogeneity of infusion treatments nested within studies using the metafor package in R. Infusing EAA was related to mean increases in MlkY and MlkP of 1.15 kg/d and 0.14%, respectively (P < 0.001). One unit increase in Met (% of MP) supplementation was associated with 1.11 kg/d greater MlkY (P = 0.047). None of the BCAA supplementations had a significant impact on the MD of MlkY, independent of Met. Net energy of lactation (NEL) had a positive effect on MlkP increment (P = 0.016) whereas Met or Lys supplementations had no effect on it. When adjusted for NEL, MlkP increments tended to be positively associated with ratios of Leu (P = 0.068) or Val (P = 0.073) supplementations to Met supplementation. EAA infusions were associated with reductions in MlkL and MlkF [0.07% (P < 0.001) and 0.09% (P = 0.091), respectively]. Increasing Met supplementation further amplified the MlkF reductions (P < 0.001). Individual BCAA may positively affect milk protein concentration when supplementations are adjusted relative to Met.