The 'male effect' in sheep and goats--revisiting the dogmas.
Male-induced ovulation in sheep and goats (the 'male effect'), documented during the period 1940-1960, has long been shrouded in preconceptions concerning how, when and why it worked. These preconceptions became dogmas but recent research is challenging them so, in this review, we have re-visited some major physiological (breed seasonality; characteristics of the response; the nature of the male stimuli) and physical factors (duration of male presence; isolation from male stimuli) that affect the phenomenon. We reject the dogma that ewes must be isolated from males and conclude that male 'novelty' is more important than isolation per se. Similarly, we reject the perception that the neuroendocrine component of the male effect is restricted to anovulatory females. Finally, we re-assess the relative importance of olfactory and non-olfactory signals, and develop a perspective on the way male-induced ovulation fits with preconceptions about pheromonal processes in mammals. Overall, our understanding of the male effect has evolved significantly and it is time to modify or reject our dogmas so this field of research can advance. We can now ask new questions regarding the application of the male effect in industry and develop research so we can fully understand this biological phenomenon.
Centro de Investigación en Reproducción Caprina, Universidad Autónoma Agraria Antonio Narro, Periférico Raúl López Sánchez y Carretera a Santa Fe, Coahuila, Mexico. joaldesa@yahoo.com
J Alberto
JA
Delgadillo
Helene
H
Gelez
Rodolfo
R
Ungerfeld
Penelope A R
PA
Hawken
Graeme B
GB
Martin
D000818:Animals; D005260:Female; D006041:Goats / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology; D007323:Instinct; D007986:Luteinizing Hormone / Q000502:physiology; D008297:Male; D010060:Ovulation / Q000502:physiology*; D010675:Pheromones; D012726:Sexual Behavior, Animal / Q000502:physiology; D012756:Sheep / Q000502:physiology*; D019147:Vomeronasal Organ / Q000502:physiology
D010675:Pheromones; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone