Las interacciones socio-sexuales, alternativa para manipular la reproducción de los pequeños rumiantes / Socio-sexual interactions, an alternative to manipulate the reproduction of small ruminants

La estacionalidad de la reproducción es una característica de la mayoría de las razas caprinas y ovinas de latitudes subtropicales. Las hembras presentan anovulación y disminución de las concentraciones plasmáticas de LH en primavera y verano, mientras que los machos disminuyen drásticamente los niveles plasmáticos de testosterona, la producción espermática y el comportamiento sexual en invierno y primavera. Esta estacionalidad es sincronizada principalmente por las variaciones naturales del fotoperiodo. Sin embargo, las interacciones socio-sexuales entre machos y hembras permiten modificar esta estacionalidad. Así, la introducción de machos en grupos de hembras en anestro estacional estimulan las actividades endocrina y reproductiva de las hembras, através del fonómeno conocido como "efecto macho". La respuesta de las hembras al efecto macho varía con la intensidad del comportamiento sexual desplegado por los machos. Por ello, los machos sexualmente activos son más eficaces que los machos en reposo sexual para estimula la ovulación de las hembras. Además, la presencia continua de los machos sexualmente activos evita la anovulación estacional, así como la disminución estacional de las concentraciones plasmáticas de LH en hembras ovariectomizadas portadoras de implantes subcutáneos que liberan estradiol. En conjunto, estos hallazgos indican que los machos cabríos y carneros sexualmente activos son una alternativa para manipular la estacionalidad reproductiva de las hembras durante el anestro estacional, y/o evitar la anovulación estacional. Además, considerando las demandas sociales para reducir o eliminar los tratamientos hormonales en la producción animal, la asociación del fotoperiodo y las interacciones socio-sexuales entre machos y hembras constituye una alternativa sustentable para la manipulación de la actividad reproductiva de los pequeños rumiantes.

A high level of male sexual activity is necessary for the activation of the medial preoptic area and the arcuate nucleus during the 'male effect' in anestrous goats.

In small ungulates such as sheep or goats, the introduction of a male among a group of anovulatory females during the anestrus season leads to the reactivation of the gonadotrope axis and ovulation, a phenomenon known as the 'male effect'. In goats, our previous studies have demonstrated the importance of male sexual activity for an efficient reactivation of the gonadotrope axis assessed through ovulation and blood LH pulsatility. In the present experiment, we assessed whether the level of male sexual activity would also induce differential activation of two brain regions of key importance for the reactivation of GnRH activity, namely the medial preoptic area and the hypothalamic arcuate nucleus. In both structures, we observed a differential activation of Fos in females, depending on the level of buck sexual activity. Indeed, goats unexposed to males showed low levels of expression of Fos while those exposed to sexually inactive bucks showed an intermediate level of Fos expression. Finally, the highest level of Fos expression was found in females exposed to sexually active males. However, and contrary to our initial hypothesis, we were not able to find any specific activation of kisspeptin cells in the arcuate nucleus following the introduction of highly sexually active males. As a whole, these results demonstrate that the level of male sexual activity is a key factor to stimulate brain regions involved in the control of the gonadotrope axis in the context of the male effect in goats.

Male goat vocalizations stimulate the estrous behavior and LH secretion in anestrous goats that have been previously exposed to bucks.

We investigated whether live vocalizations emitted by bucks interacting with anestrous females stimulate secretion of LH, estrous behavior and ovulation in anestrous goats. In experiment 1, bucks rendered sexually active by exposure to long days followed by natural photoperiod were exposed in a light-proof-building to five anestrous females. Buck vocalizations were reproduced through a microphone-amplifier-loudspeaker system to an open pen where one group of goats (n=6) was exposed for 10 days to these live vocalizations. Another group of females (n=6) was isolated from males and vocalizations. The proportion of goats displaying estrous behavior was significantly higher in females exposed to buck vocalizations than in females isolated from males. The proportion of goats that ovulated did not differ between the 2 groups (exposed to males versus isolated). In experiment 2, female goats that either had previous contact with males (n=7), or no previous contact with males (n=7) were exposed to live buck vocalizations, reproduced as described in experiment 1, for 5 days. The number and amplitude of LH pulses did not differ between groups before exposition to buck vocalizations. Five days of exposure to male vocalizations significantly increased LH pulsatility only in females that had previous contact with males, while LH pulse amplitude was not modified. We concluded that live buck vocalizations can stimulate estrous behavior and LH secretion in goats if they have had previous contact with bucks.