In : Recent Advances in

Introduction Infertility in breeding stallions contributes to low conception rates (60 65%) and substantial financial loss in the equine industry. There are a number of conditions associated with poor fertility such as mismanagement, anabolic steroid treatment, infection, fever, tumors, injury, disease, behavior or endocrine disorders [1-10]. A number of these problems can be diagnosed and treated appropriately. However, for stallions with poor sperm quality and endocrine disorders not associated with hypogonadotropic hypogonadism (abnormally low GnRH, LH, FSH and testosterone), the exact nature of their condition and the hormonal factors involved has not yet been elucidated. Previous studies in our laboratory have identified endocrine factors and mechanisms important for normal reproductive function and have demonstrated specific alterations in pituitary and testicular function between fertile, subfertile and infertile stallions [11-25]. A significant percentage of idiopathic subfertile/infertile stallions have been diagnosed with primary testicular degeneration marked by progressive softening and/or reduction of the testes, endocrine imbalance and poor seminal parameters [1,2,21]. These stallions make up a heterogeneous population of poor breeding performers with unknown pathophysiology. Recent evidence indicates that local regulatory factors such as inhibin and insulin-like growth factor-1 (IGF-1] (paracrine/autocrine factors) are important modulators of steroidogenesis and spermatogenesis [26-28]. Data generated in our laboratory support the hypothesis that the primary testicular disorder in these stallions may be, in part, an initial failure of the paracrine/autocrine system which is then followed by abnormal spermatogenesis and a hormonal imbalance [24]. If this is the case then assessing testicular function by carrying out a number of different endocrine/paracrine/autocrine tests may assist the researcher and clinician to identify the underlying cause of the problem. The tests would involve the following: