EFECTO DE LA DIETA Y DE LA MELATONINA EXOGENA SOBRE LA RESPUESTA HIPOFISARIA A LA GnRH DURANTE EL ANESTRO Y LA ESTACION REPRODUCTIVA EN OVEJAS RASA ARAGONESA

ABECIA, J A; FORCADA, F; VAZQUEZ, M.I.; PALACIN, I.

Congreso; XV Jornadas de Produccion Animal; 2013

: In order to determine the effect of level of feed intake and exogenous melatonin on pituitary responsiveness to GnRH, both during anestrus (A) and breeding season (BS), 19 OVX+E2 ewes were used. Animals were divided in 4 groups, treated (+Mel) or not (-Mel) with melatonin and fed to provide 1.5 (Control, C) or 0.5 (low, B) times maintenance requirements. Both in April and November, a GnRH challenge was performed, consisting on collecting blood samples every 10 min for 3 h. After the first hour, GnRH was injected and LH analyzed. The highest LH simple (DLH) and the area under the curve of the first h (AUC1) and the total period (AUCT) were calculated. There was a significant effect of diet (C: 0,93±0,21; B: 1,46±0,29; p<0,05) and (BS: 1,44±0,20; A: 0,96±0,19 ng/ml; p<0,05) on basal LH concentrations before GnRH challenge with no effect of melatonin. GnRH increased dramatically LH both in A and BS. DLH was not affected by melatonin, diet or season, although AUC1 and AUCT were significantly affected by season (p<0.05). The highest basal LH levels showed by undernourished ewes could be due to an increment of LH pulse amplitude described in the literature.