Preliminary investigations into the endocrine systems of subfertile cattle: location of a common lesion (rate-limiting step)

Abstract

ABSTRACT Dairy cows with a variety of clinical conditions were investigated in an attempt to identify the cause(s) of subfertility. Sequential or simultaneous injections of 20 μg gonadotrophin-releasing hormone (GnRH), 1 mg oestradiol benzoate and 0·06 mg ACTH(1–24) into five clinical cases of ovarian follicular cysts, two cases of poor body condition and one case of lameness and into control cows revealed a failure in the LH positive-feedback response to oestradiol in all eight clinical cases, but in only two out of twelve control cows. Two of the clinical cases and the two non-responding control cows had high or rising initial progesterone concentrations which would explain the absence of response. All cows studied responded similarly to GnRH and ACTH(1–24). It is suggested that hypothalamus-pituitary control of LH release may involve a rate-limiting step (in the oestradiol positive-feedback system) and that lesions at this point result in subfertility in a variety of clinical situations. J. Endocr. (1987) 113, 167–171