O Instituto de Investigação e Tecnologia da Agronomia e Meio Ambiente (IITAA) desenvolve trabalho de investigação com o objetivo de perseguir estudos em diversas áreas, como a caracterização / previsão do clima insular e os efeitos das mudanças globais em comunidades do oceano para os to... Ler mais »
Unlike most domestic livestock species, sheep are widely known as an animal with marked seasonality of breeding activity. The annual cycle of daily photoperiod has been identified as the determinant factor of this phenomenon while environmental temperature, nutritional status, social interactions, lambing date and lactation period are considered to modulate it. The aim of this paper is to review the current state of knowledge of the reproductive seasonality in sheep. Following general considerations concerning the importance of this reproductive strategy for the survival of species, it presents the different ways how both the ewe and the ram display seasonality. Both determinant and modulating factors are developed and special emphasis is given to the neuroendocrine base of photoperiodic regulation of seasonal breeding. Other aspects like the role of melatonin, the involvement of thyroid hormones and the concept of photorefractoriness are also reviewed.
Quarta, 31 Dezembro, 2003