Epsilon Archive for Student Projects

Abstract

The presence of cystic ovarian follicles represents an important ovarian dysfunction and is a major cause of reproductive failure in dairy cattle. A cystic ovarian follicle is a persistent follicular-like structure on one or both of the ovaries. It is at least 2,5cm in diameter and it has to persist for at least ten days while a corpus luteum is missing. There are two kinds of cystic ovarian follicles, those who have a progesterone production and those who have not. A clear definition for this condition is lacking, probably because the heterogeneity of the clinical signs and the complexity of the disorder. A follicle becomes cystic when it fails to ovulate and persists in the ovary. The pathogenesis of the cystic ovarian follicle is still unclear. It is generally accepted that the cause of cyst formation is disruption of the hypothalamo-pituitary-gonadal axis by endogenous and/or exogenous factors. Cows with a cystic ovarian follicle appear to be in the phase of anestrous or never leave the oestrous phase. Since the condition is treatable with GnRH there are different theories of where the disorder may origin; One is that the estrogen receptors in the hypothalamus has been down-regulated. Another hypothesis is that the LH-receptors in the follicle has been down-regulated and therefore prevents the ovulation, despite an LH-peak. This damage to the receptors in the follicles may have occurred as a result of exposure to high levels of hormones at the wrong period of time.

Mature cows suffer more frequently from ovarian cyst than younger cows. Seasonal variation occurs with cysts appearing more often in cows with parturition in the autumn than in cows with parturition in the spring. Predisposing factors for the condition have been proved to be inflammation of the uterus and shortage of energy during the first weeks of lactation.

Due to the facts I have come across, I have come to the conclusion that a cystic ovarian follicle is a reproductive distress syndrome with a metabolic origin. The hormonal imbalance is caused either by substances digested by the cow or by disrupted food supply. This disrupted food supply results in a catabolic degradation of the energy reserve of the body and the production of ketone bodies increase. The ketone bodies themselves, other metabolites which exist together with the ketones, or the reduced feed intake, may disturb the hormones that regulates the oestrus cycle.