Alterations in gonadotropin secretion and ovarian function in prepubertal gilts by elevated environmental temperature

Area of Science:

• Animal Reproduction
• Environmental Physiology
• Endocrinology

Background:

• Reproductive function in livestock can be affected by environmental factors.
• Heat stress is a significant challenge in swine production, impacting animal health and productivity.

Purpose of the Study:

• To investigate the impact of chronic heat exposure on gonadotropin secretion and ovarian function in prepubertal gilts.
• To determine if elevated environmental temperatures affect the hypothalamo-hypophyseal axis response to ovariectomy stimuli.

Main Methods:

• Prepubertal gilts were exposed to control (15.6°C) or elevated (33.3°C) temperatures from 150 to 180 days of age.
• Hormonal (FSH, LH) and ovarian responses were assessed following bilateral ovariectomy, unilateral ovariectomy, and sham ovariectomy.
• Plasma hormone concentrations were measured over a 96-hour period post-surgery.

Main Results:

• Heat-stressed gilts showed suppressed FSH and LH levels after bilateral ovariectomy compared to controls.
• Elevated temperatures abolished the FSH surge and follicular growth typically seen after unilateral ovariectomy.
• While sham ovariectomy did not alter FSH/LH secretion, heat-exposed gilts had fewer small follicles.

Conclusions:

• Chronic heat exposure diminishes the hypothalamo-hypophyseal axis's capacity to secrete FSH and LH during pubertal development in gilts.
• This impaired gonadotropin secretion has direct negative consequences on follicular development and ovarian function.
• Reduced gonadotropin secretion capacity is a key factor contributing to delayed puberty in gilts under heat stress conditions.