Development of an endocrine challenge test to investigate subfertility in ewes

Abstract

Simultaneous or sequential injection of 250 ng gonadotrophin releasing hormone (GnRH) and 25 μg oestradiol benzoate, with luteinizing hormone (LH) measurements at 0, +20 min (after GnRH) and +16 h (after oestradiol), enabled investigation of the positive feedback effects on the hypothalamus and pituitary. Control ewes had pretreatment LH values of 3·1 ± 1·2 ng/ml with an increment of 3·2 ± 2·3 ng/ml 20 min after GnRH. Subfertile ewes, in spite of elevated pretreatment LH concentrations (15·8 ± 9·5 ng/ml) in eight out of 10 ewes, had increments of 1·4–84 ng/ml after GnRH. Control ewes had LH increments of 3–75 ng/ml 16 h after oestradiol. Subfertile ewes with pretreatment LH concentrations < 15 ng/ml also responded to oestradiol whereas those with initial LH concentrations 16–40 ng/ml had no further LH increment. Subsequent administration of 1000 iu pregnant mares' serum gonadotrophin (PMSG), with measurement of LH and oestradiol at 0, +24, +30, +48, +54, and +72 h, allowed assessment of ovarian response and hypothalamus-pituitary function. Five control ewes were sampled up to 30 h post-PMSG and only 1 had oestradiol concentrations > 10 pg/ml. Sampling up to 72 h in another five control ewes resulted in oestradiol concentrations > 10 pg/ml. Increments in LH concentration > 3 ng/ml were recorded in control and subfertile ewes with oestradiol concentrations > 10 pg/ml. The use of these endocrine challenge tests enabled positive diagnosis of abnormality on 8 out of 10 occasions. Post-mortem examination of seven of the subfertile ewes revealed reproductive tract abnormalities characterized by very small inactive ovaries, and in four cases complete absence of oviducts, uterus, cervix and anterior vagina (although these latter abnormalities could not have been diagnosed from the tests described).