Natalia López-Magaña

El objetivo del presente estudio fue evaluar si la exposición al efecto macho, a los 9 o 10 meses de edad, adelanta la pubertad y mejora la fertilidad al parto en cabras nacidas en septiembre, mantenidas bajo un sistema semiextensivo con complementación alimenticia. Se trabajó con cabras de dos rebaños distintos. Las hembras fueron estabuladas desde el nacimiento, destetadas a los dos meses y manejadas en pastoreo diario junto a cabras adultas, recibiendo al finalizar una suplementación ajustada mensualmente según su peso vivo. A los 9 meses de edad (12 de junio), las hembras del primer rebaño fueron expuestas durante 15 días a machos adultos, mientras que las del segundo rebaño permanecieron aisladas de los machos. Un mes después, este segundo grupo fue expuesto a machos durante el mismo periodo. La exposición al efecto macho en junio indujo la ovulación en todas las cabras, mientras que las hembras mantenidas aisladas no presentaron actividad ovárica (P < 0,001). Cuando el segundo grupo fue expuesto a los machos en julio, todas las hembras ovularon y quedaron gestantes. Las tasas de parto no difirieron entre los dos grupos expuestos al efecto macho (P > 0,05). En conclusión, en cabras nacidas en septiembre y mantenidas bajo un sistema semiextensivo con suplementación alimenticia, la exposición al efecto macho a los 9 o 10 meses de edad adelanta el inicio de la pubertad y permite obtener elevadas tasas de fertilidad al parto.

In subtropical latitudes, goats are managed under semi-extensive systems grazing natural vegetation without supplementation. During the dry season, reduced forage availability leads to undernutrition and reduced breeding activity in bucks. This study evaluated whether pre-breeding nutritional supplementation enhances testosterone and reproductive performance in bucks joined with anestrous females. On 15 March, bucks were assigned to two groups (n = 6 each) and placed with separate flocks of 90–100 females grazing 9 h/day. Control bucks received no supplementation; supplemented bucks received 600 g/day of concentrate from 15 March to 30 May. Males were fitted with aprons until 1 June to prevent mating. Testosterone was low and similar between groups in March and April (P > 0.05). In supplemented bucks, testosterone increased from mid-May to mid-June, reaching higher than controls (P < 0.05). Females joined with supplemented bucks had higher fertility (71% vs. 53%; P < 0.01), earlier parturition, and a shorter kidding period (P < 0.0001). In conclusion, pre-breeding supplementation increases testosterone, improves fertility, and advances and synchronizes kidding under semi-extensive conditions.

Photoperiod is the main environmental factor that synchronizes the reproductive seasonality of goats. For this reason, photoperiodic treatments are used to stimulate the sexual activity in males and females during the months of the seasonal sexual rest. However, sociosexual interactions between females and males can also be used to induce the sexual activity during the resting months. Thus, bucks rendered sexually hyperactive by exposure to photoperiodic treatments are more efficient than hypoactive bucks in stimulating the reproductive activity of females during seasonal anestrus, through the phenomena called “short-term male effect” and the recently described “long-term male effect.”. Furthermore, the permanent presence of sexually hyperactive bucks prevents the seasonal anovulation, and goats ovulate all year round. Moreover, sexually hyperactive bucks are also more efficient than hypoactive bucks in stimulating the endocrine and reproductive activity of bucks during seasonal sexual rest. We recently called this phenomenon the “buck-to-buck effect”. In conclusion, sociosexual interactions allow sustainable control of the reproduction of the female and male goats.