Desarrollo del eje reproductivo endocrino en corderos de pelo

The objectives were to characterize the profiles of LH and testosterone (T) and the response to GnRH administration in hair ram lambs. Study 1: seventeen lambs were used: Blackbelly (n=4), Pelibuey (n=5), Blackbelly x Pelibuey (Crossbred; n=8). At 2, 4, 8, 12, 16, 20 and 24 wk of age, blood samples were collected every 15 min for 6 h, to characterize LH and T profiles. There was no significant difference between genotypes at any age, for any variable of LH and T profiles (P>0.05). The effect of age was significant (P<0.05): mean LH concentration was lower on wk 2 (P<0.05), achieved the highest value on wk 12, and decreased on wk 16 (P<0.05). Mean T concentration increased steadily between wk 2 and 24 (P<0.05). Study 2: twelve lambs were used: Blackbelly (n=4), Pelibuey (n=4), Crossbred (n=4). At the same ages, lambs were challenged with GnRH (3, 9, 27 ng•kg-1 BW) and blood samples were obtained between -15 and 180 min from GnRH administration. On wk 8 and 12, LH response to GnRH was greater in Pelibuey, as compared with Blackbelly. Testosterone response tended to be different between genotypes (P<0.10), with Blackbelly showing the smallest response. In conclusion, the sexual endocrine development, as evaluated by the non-stimulated LH and T profiles, was not different among genotypes; however, Pelibuey elicited the greatest responsiveness to GnRH administration at 8 and 12 wk of age. Whether or not such differences have implications on the reproductive capacity of the adult animals deserves additional research.