Growth hormone (GH) and insulin-like growth factor (IGF-I) are associated to milk production traits, however the mechanism how GH and IGF-I increase the milk synthesis remains unclear. The objective of this study was to evaluate the effect of GH and IGF-I on the synthesis and secretion of β-casein, β-lactalbumin, and lactoferrin by mammary epithelial cells. Twenty-four Saanen goats were used, and 5 goats were biopsied. Milk yield and milk quality (fat, protein, lactose and CCS) were measured daily and weekly, respectively. Growth hormone and insulin-like growth factor-I concentrations in plasma were measured once a day, at 30 and 60 d of lactation. All mammary biopsies were conducted just after blood samples. Biopsies were taken of 5 goats at 30 and 60 d of lactation. Epithelial cells were isolated and cell culture was used to study expression and synthesis of β-casein, β-lactalbumin, and lactoferrin. Four treatments were imposed to epithelial cell culture: (1) control (basal medium); (2) GH (10 ng/mL); (3) IGF-I (10 ng/mL); (4) GH + IGF-I (10 ng/mL + 10 ng/mL). The mRNA levels of β-casein, β-lactalbumin, and lactoferrin were analyzed by RT-PCR. At the same time, the synthesis of β-casein, β-lactalbumin, lactoferrin, and lactose in were measured by ELISA kit in culture medium. Statistical analysis was performed by ANOVA using mixed model, and the level of significance was set at P < 0.05 for main effects and interactions. Growth hormone (GH) and insulin-like growth factor (IGF-I) were associated with milk yield, and goats classified as higher producing (4 from 24 experimental goats) presented high GH and IGF-I levels. β-Casein expression and synthesis were significantly higher for IGF-I and GH + IGF-I treatments when compared with control. Lactoferrin expression and synthesis were significantly higher for GH and GH + IGF-I treatments when compared with control. However, β-lactalbumin expression and synthesis were not change by hormone treatments when compared with control. These results support the hypothesis that GH and IGF-I can modulate directly the synthesis of milk.