Relationships between endogenous gonadotropin-releasing hormone, gonadotropins, and follicular development after weaning in sows

Two experiments were conducted to examine relationships between endogenous gonadotropin-releasing hormone (GnRH), concentrations of gonadotropins in the anterior pituitary and blood and ovarian follicular development in weaned sows. In the first experiment, 48 sows were slaugh-tered during 0 to 5 days after weaning. Because effects of breed, parity, farm and season of slaugh-ter were confounded with day after weaning, data were analyzed solely on the basis of follicular development. Sows were divided into 4 groups based on the size and number of the largest ovarian follicles. Group 1 consisted of 11 sows with largest follicles <5 mm in diameter. Sows (n=1 1) in Group 2 had few (10) follicles 5 to 10 mm in diameter, and sows (n=11) in Group 3 had many (>14) follicles 5 to 10mm in diameter. Group 4 coniisted of sows (n=12) with follicles>10 mm in diameter. Data from 3 sows that had ovulated were omitted from the analyses. Sows in Groups 1, 2, 3 and 4 were killed atm average of 0.7 ± 0.4, 2.5 * 0.2, 4.7 ± 0.1 and 4.8 ± 0.2 days after weaning, respectively. Concentrations of GnRH in medial basal hypothalamus (MBH), stalk median eminence (SME) and hypophyseal portal area (HPA) were greater in sows with greater follicular development (Groups 3 and 4). Concentrations of luteinizing hormone (LH) in anterior pituitary (AP) an