A 5×2×2 factorial experiment was conducted using 300 Ross 305 broiler chicks aged 3 h after removing from hatcher to examine the effects on physiological adaptive parameters of post hatch fasting (PHF; 0, 12, 24, 36, and 48 h), intrayolk sac (IYS) inoculation of olive oil (0 or 0.7 ml) and sex. The weight loss percentage was significantly greater in the chicks received IYS inoculation of 0.7 ml olive oil than non-injected birds at 24, 36 and 48 h age. Yolk residual utilization was 0.0664 and 0.1011 g/h in the injected and non-injected birds, respectively, over the PHF periods of 12 to 48 h. Independent of sex, liver weight was increased (P <0.001) and breast (P <0.05) and leg percentage (P <0.05) were decreased as PHF extended from 12 to 48 h with no difference between the injected and non-injected chicks (P >0.05). Serum GLU level was decreased by 36.03 and 40.31 mg/dl in the injected and non-injected birds (P >0.05), respectively. Serum TP, ALB, CRE, URE and UA levels were significantly increased over the extended periods of fasting up to 48 h. Serum very low density lipoproteins concentration was greater in the olive oil-injected birds compared with non-injected chicks at 48 h (P < 0.05). The chicks received olive oil inoculation showed greater serum triglycerides and P concentrations than non-injected birds at 36 and 48 h of age. It was concluded that IYS inoculation of 0.7 ml olive oil did not aid the increased energy demands in the fasted neonate chicks resulting in greater weight loss and diverged metabolic responses presumably due to intensified ketosis.