The aim of this Thesis was to increase understanding of the regulation of gonadotrophin (LH and FSH) secretion in poultry with particular reference to ageing broiler breeder hens (<i>Gallus domesticus</i>). In broiler breeder hens, plasma FSH and LH were higher in peak-of-lay than in end-of-lay birds and this was correlated with higher numbers of yellow yolky ovarian follicles and pituitary common α-subunit mRNA. Old out-of-lay hens had higher pituitary FSH β mRNA and circulating FSH plasma levels than laying hens. This higher plasma FSH in out-of-lay hens was suggested to be due to a lifting of the inhibitory feedback effects of ovarian factors, probably oestrogen. Lifting feed restriction in laying broiler breeder hens increased the number of yellow yolky ovarian follicles. This was associated with an increase in hypothalamic GnRH-I and pituitary common α subunit and follistatin mRNA and plasma LH, while pituitary activin β<sub>B</sub> mRNA and plasma FSH were depressed. There was no change in other mRNAs measured, including GnIH mRNA. The expression of incubation behaviour was associated with depressed plasma LH, decreased hypothalamic GnRH-I, common α and LH β subunit mRNAs and increased GnIH mRNA. In photosensitive short day female quail, exposure to 3 long days increased ovarian weight in association with increases in common α and FSH β subunit mRNAs with no change in LH β mRNA. It is concluded that the decrease in egg laying in broiler breeders is a consequence of decreased LH and FSH secretion. The decrease in LH secretion in older hens is associated with a reduction in common α-subunit mRNA with no change in LH β subunit mRNA. In contrast to mammals, common α subunit mRNA synthesis may be a rate-limiting step in LH release in birds. The decrease in FSH secretion in older hens may be a consequence of reduced FSH β mRNA and a reduction in constitutive release.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:643176 |
| Date | January 2005 |
| Creators | Ciccone, N. A. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13399 |
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