Difference between revisions of "Seasonality of Reproduction - Anatomy & Physiology"
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| − | {{ | + | {{unfinished}} |
| + | {{toplink | ||
| + | |backcolour =EED2EE | ||
| + | |linkpage =Reproductive System - Anatomy & Physiology | ||
| + | |linktext =Reproductive System | ||
| + | |maplink = Reproductive System (Content Map) - Anatomy & Physiology | ||
| + | |pagetype =Anatomy | ||
| + | |sublink1=Reproductive System - Anatomy & Physiology#Female Reproductive Tract | ||
| + | |subtext1=FEMALE REPRODUCTIVE TRACT | ||
| + | }} | ||
| + | <br> | ||
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==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, hamster and doe have an '''anoestrus''' phase to their reproductive cycling. This means that for part of the year they are not experiencing oestrous cyclicity and so are not reproductively active. Such animals can be long 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 coincide 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. | Unlike polyoestrus animals such as the cow or sow which can reproduce all year round some species such as the mare, ewe, goat, rabbit, hamster and doe have an '''anoestrus''' phase to their reproductive cycling. This means that for part of the year they are not experiencing oestrous cyclicity and so are not reproductively active. Such animals can be long 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 coincide 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. | ||
==Mechanism of seasonality== | ==Mechanism of seasonality== | ||
| − | During the day | + | During the day lights levels are detected by the [[Special_Senses_-_Visual_-_Anatomy_%26_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 [[Endocrine System - Melatonin - Anatomy & 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 [[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. |
==Long day breeders== | ==Long day breeders== | ||
| − | |||
*The mare | *The mare | ||
*The mares breeding period is from April-June, these months having increasingly long hours of daylight. | *The mares breeding period is from April-June, these months having increasingly long hours of daylight. | ||
*Reproductive cycling occurs with increased photoperiod (increasing light levels). | *Reproductive cycling occurs with increased photoperiod (increasing light levels). | ||
| − | ==Short day | + | ==Short day breeeders== |
*Ewe, Doe, Goat | *Ewe, Doe, Goat | ||
*Their breeding season is at the end of summer and beginning of autumn. | *Their breeding season is at the end of summer and beginning of autumn. | ||
| Line 18: | Line 28: | ||
==Manipulation of Seasonal breeders== | ==Manipulation of Seasonal breeders== | ||
| − | Apart from [[ | + | 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. |
===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 [[ | + | *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. |
*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. | ||
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===Photoperiod control=== | ===Photoperiod control=== | ||
In the mare exposure to 16 hours light/day from mid november can bring the first ovulation of the breeding season forward from early april to early february, advancing pregnancy by up to two months. | In the mare exposure to 16 hours light/day from mid november can bring the first ovulation of the breeding season forward from early april to early february, advancing pregnancy by up to two months. | ||
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Revision as of 14:49, 16 September 2008
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This article is still under construction. |
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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, hamster and doe have an anoestrus phase to their reproductive cycling. This means that for part of the year they are not experiencing oestrous cyclicity and so are not reproductively active. Such animals can be long 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 coincide 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.
Mechanism of seasonality
During the day lights levels are detected by the retina which sends impulses to the suprachiasmatic nucleus of the 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 preventing synthesis of the hormone 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. 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
- The mare
- The mares breeding period is from April-June, these months having increasingly long hours of daylight.
- Reproductive cycling occurs with increased photoperiod (increasing light levels).
Short day breeeders
- Ewe, Doe, Goat
- Their breeding season is at the end of summer and beginning of autumn.
- Respond to decreased photoperiod.
Manipulation of Seasonal breeders
Apart from 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
The Mare
- 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 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.
The Ewe
- In order to produce lambs for the easter markets ewes have to be mated earlier in the year.
Photoperiod control
In the mare exposure to 16 hours light/day from mid november can bring the first ovulation of the breeding season forward from early april to early february, advancing pregnancy by up to two months.