Ž. Cystic ovarian disease COD in cows is traditionally defined as the presence of a large follicle-like structure on one of the ovaries, having a diameter of 2.5 cm or greater, Ž that persists for at least 10 days, in the absence of luteal tissue Roberts, 1986; Peter, . 1997 . The cystic structure arises from a failure to ovulate and results in a pathological Ž . Ž expression of oestrus, ranging from anoestrus most common to nymphomania Farin . and Estill, 1993 . However, more recent studies revealed that cows with cysts do not Ž. always conform to this classic definition Peter, 1997 , which seriously confounds studies on the incidence, etiology and therapy of the disease.