Changes

==Introduction==

==Introduction==

Unlike polyoestrus animals such as the cow or sow which can reproduce all year round some species such as the Mare, Ewe, Goat, Rabbit, Hampster and Doe have an '''Anoestrus''' phase to their reproductive cycling. This means that for part of the year they are not experiencing oesrous cyclicity and so are not reproductively active. such animals can be lond or short day polyoestrus breeders. seasonality of reproduction is due to the effect of light levels on the brain. Reproductive seasonality maximises the chance of offspring survival by timing parturition to coinside with spring when nutritional and climate conditions are optimum for lactation and for growth of the offspring. It is important to be able to distinguish between seasonal anoestrus and pathological infertility.

Unlike polyoestrus animals such as the cow or sow which can reproduce all year round some species such as the Mare, Ewe, Goat, Rabbit, Hampster and Doe have an '''Anoestrus''' phase to their reproductive cycling. This means that for part of the year they are not experiencing oesrous cyclicity and so are not reproductively active. such animals can be lond or short day polyoestrus breeders. seasonality of reproduction is due to the effect of light levels on the brain. Reproductive seasonality maximises the chance of offspring survival by timing parturition to coinside with spring when nutritional and climate conditions are optimum for lactation and for growth of the offspring. It is important to be able to distinguish between seasonal anoestrus and pathological infertility. Both males and females exhibit reproductive seasonality. However, the female is more strongly influenced by season.

==science of seasonality==

==Mechanism of seasonality==

During the day lights levels are detected by the [[Special_Senses_-_Visual_-_Anatomy_%26_Physiology#Optics|Retina]] which sends impulses to the [[Endocrine_System_-_Hypothalamus_-_Anatomy_%26_Physiology#Nuclei|Suprachiasmatic Nucleus]] of the [[Endocrine_System_-_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 [[Endocrine_System_-_Pineal_Gland_-_Anatomy_%26_Physiology|Pineal gland]] preventing synthesis of the hormone [[Endocrine_System_-_Melatonin_-_Anatomy_%26_Physiology|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 [[Endocrine_System_-_Pituitary_Gland_-_Anatomy_%26_Physiology|Pituitary gland]]. which effects the gonadotrophin realsing hormone (GnRH)which increases the

During the day lights levels are detected by the [[Special_Senses_-_Visual_-_Anatomy_%26_Physiology#Optics|Retina]] which sends impulses to the [[Endocrine_System_-_Hypothalamus_-_Anatomy_%26_Physiology#Nuclei|Suprachiasmatic Nucleus]] of the [[Endocrine_System_-_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 [[Endocrine_System_-_Pineal_Gland_-_Anatomy_%26_Physiology|Pineal gland]] preventing synthesis of the hormone [[Endocrine_System_-_Melatonin_-_Anatomy_%26_Physiology|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 [[Endocrine_System_-_Pituitary_Gland_-_Anatomy_%26_Physiology|Pituitary gland]]. High frequency, Low amplitude LH pulses lead to breeding activity. whereas Low frequency, high amplitude LH pulses lead to anoestrus and inactive gonads.

==Long day breeders==

==Long day breeders==

*the mare

*The mare

*The mares breeding period is from April-June as these are the months with long hours of sunlight.

*The mares breeding period is from April-June, these months having increasingly long hours of daylight.

*reproductive cycling occurs with the increasing light levels

*Reproductive cycling occurs with increased photoperiod (increasing light levels).

==short day breeeders==

==Short day breeeders==

* Ewe, Doe, Goat

*Ewe, Doe, Goat

'''The Ewe'''

'''The Ewe'''

*In order to produce lambs for the easter markets ewes have to be mated earlier in the year.

*In order to produce lambs for the easter markets ewes have to be mated earlier in the year.