Adminlstración de pulsos de GnRH a cerdas lactantes y su efecto sobre el estro y la ovulación

Ten pimiparous Landrace x Yorkshire or Hampshire sows nursing 9.3±1.2 piglets were used to determine whether induction of ovulation required continued of pulsatile gonadotropin-realeasing hormone (GnRH) beyond the onset of estrus. Beginning at 23.8±0.3 d of lactation, all sows received 1.5 ug GnRH every h unit until onset of estrus, which occurred 123 ± 7 h after GnRH began. The GnRH was terminated either 0 (n=5) or 24 h (n=5) after on set of estrus. Blood samples were obtained at 12 h intervals after onset of estrus. Prior to estrus LH and FSH averaged 0.6±0.1 and 0.4±0.1 ng/ml, respectively. Concentrations of the LH preovulatory peak FSH surges lasted approximately 18 h, then returned to less than 1 ng/ml, and there were no treatment differences. Concentrations of the LH preovulatory peak tended to be greater for sows in the 24 h than in the 0 h group (2.5±0.2 vs 1.9±0.3 ng/ml, P<0.10). Interval from the onset of estrus to LH peak (2.8± 0.8 h) was not affected by treatment. Concentrations of FSH (0.8±0.2 ng/ml) peaked at 6.2±1.9 h. Number of corpora lutea present al laparotomy on day 14 post estrus was 18.0±1.7 and 17.4±1.7 for 0 and 24 h treatment groups. Three sows from 0 group had follicular cysts, 20 mm in diameter, and one had ectopic follicles. Interval from the onset of treatment to estrus was linearly related to the number of pigs nursed (P<0.01, r= 0.82). The equation for this relationship was Y= 9.59 x+34.01, where y= hours to estrus and x= number of pigs nursed. We conclude that once proestrous hormonal changes had been induced by pulsatile GnRH, lactational factors which normally suppress gonadotropin secretion did not interfere with preovulatory ganadotropin secretion and ovulation rate.