One possible strategy to optimize breeding programmes in terms of feed costs is selecting animals based on their genetic performance over protein levels (PL). A genotype and environment (G×E) interaction in which the gradual environmental changes are represented by the respective PL is such a strategy. Reaction norm models (RNM) are suitable to perform these analyses, since they enable to evaluate genetic differences among animals as well as variance components and heritability estimates over PL. The aim of the study was to investigate the G and PL interaction in two meat-type quail lines (UFV1 and UFV2) for their body weight at day 28 (BW28) and 35 (BW35) of age by using RNM. Diets were composed in order to have different PL (22, 23, 24, 25, 26, 27, 28 and 29%) but the same metabolizable energy (2900 kcal) by keeping constant amino acids : lysine ratio for animal performance. The data set contained 970 and 410 animals from UFV1 and UFV2 lines, respectively. Several RNM (with different Legendre polynomial orders and residual variance classes) were compared via Akaike (AIC) and Schwarz Bayesian (BIC) information criteria. The RNM outperformed (lower AIC and BIC values) the traditional model disregarding G×E and suggested G×PL interaction for BW28 and BW35. The observed moderate-to-high heritabilities increased over PL, thus proving the existence of G×PL for growth traits in meat-type quail.