hormones and pregnancy in animals

8/3/2019 Hormones and Pregnancy in Animals

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AbstractPregnancy is the main event in the life of a female mammal to reproduce

its progeny and maintain the integrity of the species. It is a very

coordinated process involving reproductive organs and changes in thetissue concentration of various hormones, cytokines, enzymes and

growth factors, of which hormones are most important. Pregnancy

mainly involved two hormones, namely progesterone and estrogen.

Other hormones involved in this process are prostaglandin, cortisone,relaxin and oxytocin, which are mainly important for parturition.

Pregnancy involves two major events establishment and maintenance.

Establishment provides maternal recognition of presence of conceptus

for subsequent preparations. This is achieved by ovine interferon tou,

bovine interferon tou, estrogen and interferon in sheep, cattle, pig and

horse respectively. Hormonal control for maintenance of pregnancy

involves prevention of uterine contraction by progesterone block in farm

animals. The source of progesterone and control of its production differs

between species and stage of pregnancy. Cow, sow and goat are


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The period offetal developmentbeginning withfertilization and

ending withparturition.

Leonardo da Vinci, "The Foetus in Utero,"1489

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Two majorevents of

pregnancy

are:

Maternalrecognition of

pregnancy

Maintenanceof pregnancy

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Pregnancy recognitionfactors

bINF-T Bovine

interferon-T

oINF-T Ovineinterferon-T

E2 Estradiol

hCG Humanchorionic

gonadotropins

It is a process

of providing

signal tothe mother,

to prevent

the destructionof the CL.

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For maintenance of pregnancy progesterone level should be continuouslymaintained.

The source of progesterone and control of its production differ between speciesand stages of pregnancy.

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Estrogen

The main role of estrogen in early gestation is to primetissues for progesterone action. Part of this function isexerted in the uterus by enhancing epithelial cellmultiplication and hypertrophy of the uterine smooth

muscle.

It also facilitates the deposition of glycogen in the uterinemuscle and increases vascularisation of the uterus.

Later in gestation, it increases uterine metabolism tocope with the increasing growth requirements of thefoetus.

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Progesterone

Progesterone stimulates development of endometrialglands and the production of histotroph or uterine milk.

Close to parturition progesterone stimulates lobulo-alveolar growth in the mammary gland.

Finally, progesterone produces modifications in thebehaviour of the pregnant animal that are conducive forpregnancy maintenance.

The other essential action of progesterone is to maintainuterine quiescence which permits the attachment andmaintenance of pregnancy.

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Follicle stimulatinghormone

Only in mares initially

supports thedevelopment of

follicles for secondarycorpus luteum ( CL) ,this is also known as

eCG in this case.

Luteinizing hormone

During early

pregnancy, LH is

required as a

luteotropin to maintain

the CL functioning

properly.

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O t i


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Relaxin

Low in early pregnancy

Unknown origin

Suspected placenta

Produced by regressing

CL and placenta at theend of pregnancy forrelaxation of pelvicligaments.

Oxytocin

Triggers production ofPGF2.

Stimulates smooth musclecontractility.

A luteolytic role, throughstimulation of uterine has

been determined in thecow and ewe. In pregnant, synthesis is

blocked by conceptus. In late pregnancy,

synthesis increases andinvolves in parturition andmilk let down.

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"ovine interferon tau (oIFN-t)provides signal for maternalrecognition of pregnancy.

The oIFN-t acts on theendometrium of the uterus toprevent the synthesis ofPGF2a. Thus by preventingsynthesis of the luteolytic

agent, PGF2a, the CL isprotected and maintained.

Corpus luteum ofewe

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The CL and anteriorpituitary LH needed to

cause secretion ofprogesterone areessential for the first 55

days of ovinepregnancy.

Thereafter the placentaproduces sufficientprogesterone formaintenance of

pregnancy until the endof the 146 day gestationwhen the placenta

converts its producedprogesterone to

estrogen.4/27/2012 12


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Maternal

recognition occursin between day 16and 19.

Bovine interferon

tau is responsible forthis.

The CL and ovarianprogesterone are

essential forpregnancy

maintenancethroughout the 280

day bovine

gestation. Corpus luteum ofcattle4/27/201213


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Estrogen produced by

conceptus at day 11 and12 leads to maternal

recognition of pregnancy.

This estrogen doesnt

appear to inhibit uterineproduction ofPGF2a, butcause it to be

sequestered in uterinelumen resulting in

unavailability to causeluteolysis ( endocrine

exocrine model ofmaternal recognition of

pregnancy).

Progesterone from the CL

and CL maintenance areessential for maintenanceof pregnancy in thisspecies throughout the114 day gestation.

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It is likely that conceptus

derived proteins likeinterferon tau at day 11onwards is responsible formaternal recognition of

pregnancy.

The conceptus migrateswithin the uterine lumen

from one horn o the other10 13 times per day

between day 10 and 16 ofpregnancy, likely in an

effort to inhibit or modifyendometrial PGF2a

production.

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Primary corpus luteum maintains

pregnancy till 35 days.

Then, endometrial cups will produceequine chorionic gonadotropin, which

induces secondary corpus luteumformation. This maintains pregnancy till150 days.

After day 150 onwards progesteronehormone is synthesized by placenta.

Mare will remain pregnant when theovaries are removed after day 70.

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Fig: Hormonal profile of equine pregnancy

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Maternal recognition and maintenance aretwo major physiological processes ofpregnancy.

Interferons, estrogen etc. are responsible formaternal recognition by inhibiting PGF2arelease or altering its releasing pattern.

Progesterone maintains pregnancy. Source ofprogesterone ,however, varies according to

species and even with stages of pregnancy.4/27/2012 19


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Sow, cow, goat etc. are dependent on CL forpregnancy whereas, ewe and mare areplacenta dependent for progesteronerelease.

Any fluctuation in hormonal profile may lead

to abnormality of pregnancy like abortion.

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Anonymous. Equine Pregnancy. Retrieved on 2011-6-25 fromhttp://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/equine

pregnancy.htmBate, L. A. Pregnancy and Parturition. Retrieved fromhttp://people.upei.ca/bate/html/pregnancyandparturition.html

Hafez and Hafez. 2005. Reproduction in Farm Animals. Seventh edition.

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

Kiyoshi Okuda. Basics of Reproductive Bioscience and Biotechnology - Hormones forregulating ovarian function and its application in animal breeding. OkayamaUniversity. Laboratory of REPRODUCTIVE ENDOCRINOLOGY.

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

Nasar A. and A. Rahman. Hormonal Changes in the Uterus During Pregnancy-Lessonsfrom the Ewe: A Review. Journal of Agriculture & Rural Development

Roberts S.J. 2004. Veterinary Obstetrics and Genital Diseases. Second edition. CBSpublishers and distributers.

Senger, P.L.. Pathways to Pregnancy and Parturition. Pullman: Current Conceptions,Inc., 2003.

Spencer TE, Burghardt RC, Johnson GA and Bazer FW. 2004. Conceptus signals forestablishment and maintenance of pregnancy. Retrieved on 2011-6-25 from

http://www.ncbi.nlm.nih.gov4/27/2012 21
http://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/abberations2.htmhttp://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/abberations2.htmhttp://people.upei.ca/bate/html/pregnancyandparturition.htmlhttp://www.ncbi.nlm.nih.gov/http://www.ncbi.nlm.nih.gov/http://people.upei.ca/bate/html/pregnancyandparturition.htmlhttp://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/abberations2.htmhttp://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/abberations2.htmhttp://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/abberations2.htmhttp://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/abberations2.htm


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You havementioned onyour abstractabout

progesteroneblock, whatdoes it mean ?

Well, progesterone isthe hormoneresponsible for

maintenance ofpregnancy byblocking the uterinemotility and otherassociated factorsresponsible for loss ofconceptus, and this

is known asprogesterone block.

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Y ti d Yep in all species which


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You mentioned,ovariectomyafter 70 days

maintainspregnancy inmare, does ithappen in otherspecies as welland is their anyindication for this

ovariectomy inmare ?

Yep, in all species whichare placentaldependent forprogesterone synthesisduring pregnancy,

ovariectomy can bedone without hamperingdevelopment of fetus.But this should be doneafter placenta fully takesover the function of

progesterone synthesis.Regarding indication ofovariectomy duringpregnancy in mare, I wasjust mean to say they areplacental dependentand I know no any suchindications except forgeneral indications likeduring ovarianpathologies.

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I h l Actually its interesting


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In hormonalprofile graphunlike in others

estrogen level ishigh in pig inearly days , whyand what is itsphysiologicalrole?

Actually, its interesting.Unlike in others species, inpig estrogen helps inmaternal recognition andthis early rise if for this

purpose. Estrogen in pig,modifies the releasingmechanism ofprostaglandin. In otherspecies prostaglandin isreleased in uterine vessels

so that they can act onCL but in pig estrogenleads their release intothe uterine lumen so thanthey are instead excretedin urine and the CL isestablished. For thisvarious ion channels andsecond messengersystems are involved.

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hormones and pregnancy in animals

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