Sokoine University of Agriculture

Photoperiodic control of seasonal breeding

Show simple item record Bunyaga, A. S. Makungu, M. 2018-10-30T05:24:46Z 2018-10-30T05:24:46Z 2018
dc.identifier.citation Bunyaga, A.S. Makungu, M. (2018). Photoperiodic Control of Seasonal Breeding. Journal of Open University of Tanzania, 25(1): 126-144 en_US
dc.identifier.issn -
dc.description Huria Journal, 2018; 25(1): 126-144 en_US
dc.description.abstract Photoperiod is a powerful synchronizer of seasonal changes in endocrine and metabolic physiology in vertebrates living in tropical to polar zone. The purpose of this review is to study the factors which are involved in the process of photoperiodism in control of seasonal breeding in birds and mammals. The gonadotropin-releasing hormone (GnRH) is crucial in seasonal breeding mammals and birds, whereby under the influence of thyroid hormone, triiodothyronine (T3), it stimulates the anterior pituitary gland to release gonadotropins responsible for maturation of reproductive organs. The process that leads to stimulation of GnRH production differs between birds and mammals. In birds, light is perceived by deep brain photoreceptors and long day induced thyroid-stimulating hormone (TSH) causes local T3 activation. In mammals, light is perceived by the eyes and melatonin which is secreted during the night from the pineal gland regulates TSH. Therefore eyes, pineal gland and melatonin are not essential for regulation of seasonal reproduction in birds. Despite the differences, birds and mammals are subjected to common features i.e. light exposure and TSH during photostimulation. Long photoperiod causes photostimulation followed by photorefractoriness. The latter, has been thought to occur due to the influence of prolactin. The initial gonadal regression which is encountered during photorefractoriness occurs while there is still releasable GnRH. The timing of photorefractoriness is influenced by food availability, temperature and social factors like songs. The dissipation of photorefractoriness occurs during short photoperiods and is characterized by an increase in hypothalamic GnRH en_US
dc.description.sponsorship - en_US
dc.language.iso en en_US
dc.publisher Open University of Tanzania en_US
dc.relation.ispartofseries 25(1):126-144;
dc.subject Photoperiodism en_US
dc.subject Birds en_US
dc.subject Mammals en_US
dc.subject Thyroid en_US
dc.subject Gonadotropin en_US
dc.title Photoperiodic control of seasonal breeding en_US
dc.type Article en_US
dc.url en_US

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