COX-1 mRNA expression in ovaries of hens at approximately 6 month intervals. Normal ovaries of 2.5 year old hens (n=18) had significantly greater expression of COX-1 mRNA than 1 (n=20), 1.5 (n=20) and 2 (n=20) year old hens. A significant elevation in COX-1 mRNA expression occurred in ovaries of 3 year old normal hens (n=7) compared to ovaries of 2.5 year old normal hens. There was a significant difference in COX-1 mRNA expression between normal and cancerous ovaries of hens at 2.5, 3 and 3.5 year old. a versus b, b versus c, b versus d, c versus e, e versus d, P<0.01; c versus d, P>0.05. Bars indicate standard error.