effect of photoperiod on reproduction of sheep and horse

EFFECT OF PHOTOPERIOD ON REPRODUCTION OF SHEEP AND HORSE

Welcome to the clinical conference presentation

Topic of interest

Santosh DhakalB.V.Sc. and A.H. 9th sem.Roll no: 25

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PHOTOPERIOD AND PHOTOPERIODICITY

Duration of light an animal is exposed to, in a day.

Long day photoperiod (LDPP) :-16 - 18L / 6- 8D

Short day photoperiod (SDPP) :- 8L / 16D

Photoperiodicity is the physiological reaction of organisms to the length of day or night.

What body does against or in accordance with light or darkness is photoperiodicity.

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PHOTOPERIOD AND REPRODUCTION Photoperiod regulates cyclicity in seasonal breeders.

Seasonal breeders are those animals which become ready for breeding only on a particular season

Short day breeders: those breed in short photoperiod Long day breeders: those breed in long photoperiod

The mammalian pineal gland ( third eye) appears to be a major endocrine component in the regulation of photoperiodic responses.

Pineal gland produces melatonin ( dark hormone) in response to photoperiod that controls GnRH and LH synthesis

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PHOTOPERIOD AND MELATONIN SYNTHESIS

Melatonin is hormone of darkness. So melatonin production is less during long photoperiod and high in short photoperiod.

It is synthesized from serotonin in two steps

The mechanism behind this pattern of secretion during the dark cycle is that activity of the rate-limiting enzyme in melatonin synthesis - serotonin N-acetyltransferase (NAT) - is low during daylight and peaks during the dark phase.

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SEASONALITY IN SHEEP AND HORSE

Most sheep are seasonally polyestrous and short-day breeders.

It is because in sheep melatonin enhances GnRH synthesis.

Most horses are also seasonally polyestrous but long day breeders.

In horse melatonin suppresses GnRH synthesis.

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EFFECT OF SHORT PHOTOPERIOD Sheep Horse

Short photoperiod ( decrease light)

Firing of retinal nerves

Excitation from superior cervical ganglion

Pineal gland activity (NAT enzyme)

Melatonin

symbol:

Enhance GnRH

Suppress

FSH / LH

seasonal cyclicity. Seasonal anestrous.

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EFFECT OF LONG PHOTOPERIODSheep Horse

Long photoperiod ( increase light)

Firing of retinal nerves

Excitation from superior cervical ganglion

Pineal gland ( NAT synthesis)

Melatonin

GnRH

FSH /LH

seasonal anestrous seasonal cyclicity.

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DURING NON- BREEDING SEASON

In maleSperm production decreases.Abnormal spermatozoa increases.Fertility decreases.

In femaleOvaries are inactive.No dominant follicles are present.No behavioral estrous.

During breeding seasonIn maleSperm production increases.Abnormal spermatozoa decreases.Fertility increases.

In femaleOvaries are active.Follicles are present.Behavioral estrous.

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ARTIFICIAL MANAGEMENT OF PHOTOPERIOD TO CONTROL REPRODUCTION

In sheep and horse, photoperiod can be altered artificially to bring them in heat.

In sheep, dark period can be increased to allow more melatonin synthesis and hence to allow for reproductive performance or synthetic melatonin can be administered.

In horse, lightening hour should be increased to bring them into cyclicity.

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CONCLUSION Photoperiod is responsible for maintaining

seasonality in sheep and horse. It affects on reproduction by its action on pineal

gland which synthesizes melatonin. Melatonin is synthesized at night. In sheep melatonin enhances GnRH synthesis so

sheep are short day breeders. In horse melatonin suppresses the synthesis of

GnRH so they are long day breeders. Photoperiod can be controlled artificially to drive

the reproductive behavior in our desired direction.

However the biasness of melatonin action on these two species of animal is still a topic of research.

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BIBLIOGRAPHY

Anonymous. Seasonality of Reproduction. 2008. http://www.ttuhsc.edu/som/obgyn/faculty/Prien/Lecture%20notes/ASFT3401/reproduc.htm. Retrieved on 2011-5-23.

Bowen, R.. "The Pineal Gland and Melatonin".2009. http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html. Retrieved on 2011-5-23.

Barbara A. M. 2011. Absence of a serum melatonin rhythm under acutely extended darkness in the horse. Journal of Circadian Rhythm. Retrieved on 2011-5-23.

Choosing the right breeding season for horses. www.horseandhound.co.uk. Retrived on 2011-5-23.

Goldman and Darrow. The Pineal Gland and Mammalian Photoperiodism. www.PubMedresult.htm . Retrieved on 2011-5-23.

Hafez E.S.E. and B. Hafez. 2000. Reproduction in Farm Animals. 7th edition.Horse breeding. www.horses-and-horseinformation.com Retrieved on 2011-5-23.

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Johnson, M.H., and Barry Everitt. Essential Reproduction. Blackwell Publications, 1999. Retrieved on 2011-5-23.

McKinnon, A.O. and J. L. Voss. 1993. Equine Reproduction. LEA and FEBIGER publication, Philadelphia, London.

Notter, D.R, "Opportunities to Reduce Seasonality of Breeding in Sheep by Selection". http://www.ansci.wisc.edu/Extenstion. Retrieved on 2011-5-23.

Reproduction in Horse. www.univet.hu. Retrieved on 2011-5-23.Schoenian. "Sheep 201". 2009. http://www.sheep101.info/201/ewerepro.html.

Retrieved on 2011-5-23.Seasonal breeding. en. wikipedia.org. Retrieved on 2011-5-23.Seasonal breeding in sheep. www.ansci.wisc.edu.com Retrieved on 2011-5-23.Seasonal breeding in Sheep – Mechanism of action of melatonin.

linkinghub.elsevier.com Retrieved on 2011-5-23.Senger, P.L.. Pathways to Pregnancy and Parturition. Pullman: Current Conceptions,

Inc., 2003.

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16Thank You for Your Patience.

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