Changes

==Mechanism of seasonality==

==Mechanism of seasonality==

During the day, light levels are detected by the [[Eye - Anatomy & Physiology#Optics|retina]] which sends impulses to the [[Hypothalamus_-_Anatomy_%26_Physiology#Nuclei|suprachiasmatic nucleus]] of the [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]] and then to the superior cervical ganglion. Postganglionic nerve fibres synapse with inhibitory nerve fibres within the pineal gland. These fibres cause inhibition of the pinealocyte cells of the [[Pineal_Gland_-_Anatomy_%26_Physiology|pineal gland]] preventing synthesis of the hormone [[Melatonin|melatonin]]. At night there is reduced retinal firing and so reduced inhibition of pinealocytes by postganglionic superior cervical gangion fibres and so melatonin is synthesised and released. Melatonin stimulates the synthesis and release of GnRH from the hypothalamus leading to pulses of luteinising hormone release from the [[Pituitary_Gland_-_Anatomy_%26_Physiology|pituitary gland]]. High frequency, low amplitude LH pulses lead to breeding activity. Where as low frequency, high amplitude LH pulses lead to anoestrus and inactive gonads.

During the day, light levels are detected by the [[Eye - Anatomy & Physiology#Optics|retina]] which sends impulses to the [[Hypothalamus_- Anatomy & Physiology#Nuclei|suprachiasmatic nucleus]] of the [[Hypothalamus_- Anatomy & Physiology|hypothalamus]] and then to the superior cervical ganglion. Postganglionic nerve fibres synapse with inhibitory nerve fibres within the pineal gland. These fibres cause inhibition of the pinealocyte cells of the [[Pineal_Gland_- Anatomy & Physiology|pineal gland]] preventing synthesis of the hormone [[Melatonin|melatonin]]. At night there is reduced retinal firing and so reduced inhibition of pinealocytes by postganglionic superior cervical gangion fibres and so melatonin is synthesised and released. Melatonin stimulates the synthesis and release of GnRH from the hypothalamus leading to pulses of luteinising hormone release from the [[Pituitary_Gland_- Anatomy & Physiology|pituitary gland]]. High frequency, low amplitude LH pulses lead to breeding activity. Where as low frequency, high amplitude LH pulses lead to anoestrus and inactive gonads.

==Long day breeders==

==Long day breeders==

==Manipulation of Seasonal breeders==

==Manipulation of Seasonal breeders==

Apart from [[Oestrous_Cycle_-Pharmacological_Manipulation_of_Oestrous_Cycles_-_Anatomy_%26_Physiology|pharmalogical manipulation]] of the oestrous cycle, photoperiod, nutrition and temperature may also play a part in the controlling entry into the breeding season in some species.

Apart from [[Oestrous_Cycle_-Pharmacological_Manipulation_of_Oestrous_Cycles_- Anatomy & Physiology|pharmalogical manipulation]] of the oestrous cycle, photoperiod, nutrition and temperature may also play a part in the controlling entry into the breeding season in some species.

===Reasons for controlling breeding seasons===

===Reasons for controlling breeding seasons===

'''The Mare'''

'''The Mare'''

*To shorten the Anoestrus period after foaling.

*To shorten the Anoestrus period after foaling.

*In order to synchronize a group of mares so that they may all be mated at the same time or to make [[Reproductive_Technologies_-Multiple_Ovulation_and_Embryo_Transfer-_Anatomy_%26_Physiology|Embryo Transfer]] possible.

*In order to synchronize a group of mares so that they may all be mated at the same time or to make [[Reproductive_Technologies_-Multiple_Ovulation_and_Embryo_Transfer- Anatomy & Physiology|Embryo Transfer]] possible.

*Control of entry into the breeding season is particually important in producing foals for the racing industry. Racehorses run from the age of two years old, with the age of the horse being measured from the 1st of January. Producing horses born as close to the 1st of January as possible gives them a performance advantage when racing.

*Control of entry into the breeding season is particually important in producing foals for the racing industry. Racehorses run from the age of two years old, with the age of the horse being measured from the 1st of January. Producing horses born as close to the 1st of January as possible gives them a performance advantage when racing.