Cortisol is essential for copious synthesis of milk components, and cortisol administration delayed the decline of milk yield in late lactation. However, the effect of cortisol in proliferation, activity, and survival of the epithelial cells remains controversial. The objective of this study was to evaluate the effect of cortisol on the survival and proliferation of epithelial cells. Twenty-four Saanen goats were submitted to administration of ACTH (Cortisol group) or placebo (Control group). Milk yield and milk quality (fat, protein, lactose, and CCS) were measured daily and weekly, respectively. Cortisol concentrations in plasma were measured before and after ACTH or Placebo administration at 60, 90, and 120 d of lactation. All mammary biopsies were conducted 1 h after ACTH or placebo administration. Biopsies were taken of 4 goats submitted to ACTH and 4 goats submitted to placebo at 60, 90 and 120 d of lactation. Apoptosis was determined using terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) kit, and proliferating cell was determined using a proliferating cell nuclear antigen (PCNA) kit. The mRNA levels of Bax and Bcl-2 were analyzed by RT-PCR. At the same time, Bax and Bcl-2 synthesis were measured by ELISA kit. 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. Although, cortisol increased significantly after ACTH administration milk yield, milk quality, casein and lactose in milk were similar for both groups. Furthermore, percentage of apoptotic cells measured by TUNEL, percentage of proliferation measured by PCNA, and the expression and synthesis of Bax (promoter of apoptosis) were similar in ACTH and placebo groups (control). However, the expression and synthesis of Bcl-2 (inhibitor of apoptosis) were significantly higher after ACTH administration when compared with placebo administration. Furthermore, the relationship between Bax/Bcl-2 was significantly lower after ACTH administration when compared with placebo administration. These results support the hypothesis that cortisol can delay apoptosis in the mammary gland.