Gerardo Duarte

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Melatonin transduces the effect of day length on LH secretion by acting on the hypothalamus. However, the precise hypothalamic site is unknown. Two studies were undertaken to clarify where melatonin acts in the hypothalamus. Using autoradiographic methods, the hypothalami of 5 ewes were screened to determine whether specific regional densities in melatonin(More)
Two experiments were conducted to determine the response of Creole male goats treated with long days and melatonin implants, and the response of the anovulatory does to male effect using males treated only with artificially long days. All animals were allocated to open sheds. In Exp. 1, one group of males was under natural photoperiod (CG; n = 7); the(More)
The aim of this study was to determine whether the seasonal change in food availability provides a predictive cue that synchronizes the breeding season in goats adapted to the subtropical conditions of Northern Mexico. Groups of multiparous intact (n=7) and ovariectomized does bearing a subcutaneous implant constantly releasing estradiol-l7 beta (OVX+E;(More)
Bucks rendered sexually active by a photoperiod treatment of long days can induce fertile ovulation in a group of goats with only 4 h of contact daily with a male:female ratio of 1:10. Here we tested whether such bucks could induce fertile ovulations when stimulating successively three different groups of anovulatory goats when interacting 4 h per day(More)
The response of male goats exposed to different durations of long days (LD) during an extra-light treatment in autumn-winter, and their ability to induce ovulations in seasonally anovulatory goats were investigated in 2 experiments. In experiment 1, control males were exposed to natural photoperiod (n = 5), whereas 4 additional groups (n = 5/group) were(More)
Under temperate and subtropical latitudes, ewes and goats display a reproductive seasonal pattern and their sexual activity during the anestrous period can be stimulated and synchronized by the introduction of males in the group, which is called the "male effect". The response of females to the male effect in the middle of the anestrous season is weak or(More)
Two experiments were conducted to (a) determine whether sexually active males are able to stimulate the sexual activity of anestrous female goats when duration of contact is reduced to an intermittent contact shorter than 4 daily hours and (b) compare the pattern of secretion of LH when anestrous goats are exposed either permanently or intermittently to(More)
Sexual activity in sheep is under photoperiodic control, which is the main environmental factor responsible for the seasonality of reproduction. However, other natural environmental factors such as presence of conspecifics can slightly influence the timing of onset and offset of the breeding season. In goats, we have found that the continuous presence of(More)
The aim of this study was to determine whether the sexual activity of local male Creole goats in subtropical Mexico can be induced during the non-breeding season by a long-day treatment followed by insertion of two melatonin implants. The experiment was carried out in the Laguna region in the State of Coahuila, Mexico (26 degrees N). Fourteen male goats(More)
The aim of this study was to determine whether the reproductive seasonality of local male goats from subtropical Mexico (26 degrees N) is controlled by photoperiod. The control group (n = 7) remained in an open shed under natural daylight. The two experimental groups (n = 6 each) were placed in light-proof buildings and exposed for 2 years (yr) to(More)