concentration in ovaries. (A) The hens treated with 100 mg/kg (n=6; P<0.001) and 175 mg/kg fish oil (n=8; P<0.01) had lower concentrations of PGE2 in the ovaries compared to ovaries of control hens (n=8). (B & D) There were no significant differences in expression of EP4 among groups (P>0.05). (C) After 3 weeks of fish oil supplementation, the egg laying frequency of hens that were treated with 100 mg/kg fish oil was significantly increased compared to the ovulation rate of the same group on first week and ovulation rate of control group on third week (P<0.05). The ovulation rate in 700 mg/kg fish oil-treated hens was significantly decreased in weeks two and three compared to week one (P<0.05). *, P<0.05; **, P<0.01; ***, P<0.001. Bars indicate standard error.