Photoperiodic control of seasonal breeding

Bunyaga, A. S.; Makungu, M.

dc.creator	Bunyaga, A. S.
dc.creator	Makungu, M.
dc.date	2018-10-30T05:24:46Z
dc.date	2018-10-30T05:24:46Z
dc.date	2018
dc.date.accessioned	2022-10-25T08:53:08Z
dc.date.available	2022-10-25T08:53:08Z
dc.identifier	Bunyaga, A.S. Makungu, M. (2018). Photoperiodic Control of Seasonal Breeding. Journal of Open University of Tanzania, 25(1): 126-144
dc.identifier	-
dc.identifier	https://www.suaire.sua.ac.tz/handle/123456789/2663
dc.identifier.uri	http://hdl.handle.net/123456789/93398
dc.description	Huria Journal, 2018; 25(1): 126-144
dc.description	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
dc.description	-
dc.format	application/pdf
dc.language	en
dc.publisher	Open University of Tanzania
dc.relation	25(1):126-144;
dc.subject	Photoperiodism
dc.subject	Birds
dc.subject	Mammals
dc.subject	Thyroid
dc.subject	Gonadotropin
dc.title	Photoperiodic control of seasonal breeding
dc.type	Article