Pregnancy and Its Duration

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Welcome to Clinical Conference

Pregnancy and its durationSaluna Pokhrel

Roll no: 22

9th

semester, B.V.Sc & AH


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Abstract Farm animals are viviparous, they complete their embryonic and fetal

development within the uterus. The period of intrauterine development fromthe time of fertile mating to the parturition is termed as pregnancy. It is alsocalled as gestation. Duration of pregnancy is genetically determined althoughit can be modified by maternal, fetal, genetic and environmental factors. Theduration of pregnancy differs with species as: cattle (9 months 9 days),buffalo (10 months 10 days), sheep (5 months 5 days), goat (5 months + 5days), pig (3 months, 3 weeks, 3 days), horse (11 months 11 days), dog (2

months 2 days), rabbit (1 month 2days). Changes in reproductive organsincludes, highly edematous and vascular vulva in later stage of pregnancy,closed cervix, enlargement of the uterus, persistence of corpus luteum andrelaxation of pelvic ligaments. Pregnancy is maintained by the increased levelof progesterone and reduced level of estrogen. Fetus is nourished by maternalenvironment through placenta whose size and function changes continuouslyduring the course of pregnancy.

Key words: Pregnancy, Gestation, Corpus luteum, Progesterone, Estrogen

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Pregnancy

Pregnancy or gestation is the periodfrom fertilization or conception, to

parturition or birth of the young.

During this period single cells divideand develop into highly organizedindividuals.

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Female reproductive tract4


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Stages of pregnancy

Period of ovum or blastula

Period of embryo and organogenesis

Period of fetus and fetal growth

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Period of the ovum or blastula

10-12 days in the cow.

Division or cleavage of the fertilised ovum.

Progresses in the region of ampullary-isthmicjunction of the oviduct to the morula stage.

Morula enters the uterus and forms blastocyst.

Defective ova die and are absorbed.

CL is developing.

Progesterone is increasing.

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Period of embryo and organogenesis

12-15 days to about 45 days in cow.With the rapid genetic encoding, major tissues and

organs systems are formed.

Species of the embryo is readily recognizable at theend of this period.

Trophoblast extends very rapidly and extends into theopposite horn by 19 days.

Embryo may die, be expelled unnoticed at the nextestrum, or become macerated and absorbed withoutexternal signs.

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Period of fetus and fetal growth

34 days in sheep and dog, 45 days in cattle, 55 days inhorse to parturition.

Differentiation and growth of organs, tissues andsystems .

Caruncles and cotyledons develop and enlarge tosupply nutrition to the fetus.

From 210-270 days, increase in weight of the bovinefetus is equal to 3 times from the time of fertilizationto 210 days.

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Duration of pregnancy

Animal Length

Cattle 9 months 9 days

Buffalo 10 months 10 days

Sheep 5 months 5 days

Goat 5 months + 5 days

Pig 3 months, 3 weeks, 3 days

Horse 11 months 11 days

Dog 2 months 2 daysRabbit 1 month 2 days

Llama 11 months (350 days)

Human 259-294 days

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Maternal recognition of pregnancy

It is the process whereby luteolysis is prevented bythe presence of the conceptus which prolongsprogesterone secretion for the maintenance of

pregnancy.

In ruminants, the trophoblast of the developingconceptus blocks luteal regression by the production

of interferons (IFNs).

In pigs, production of estrogen by the blastocyst wasthought to be the signal controlling MRP.

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Reproductive organ changes

Vulva and vaginal

Vulva becomes highly edematous and vascular.

Vaginal mucosa is pale and dry.

Cervix

Tight closure of the external os by highly viscid mucus seal.

Uterus

Gradual enlargement but the myometrium remainsquiescent.

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Reproductive organ changes contd

Ovary

CL verum persists, as a result estrous cycles are suspended.

These follicles lutenize to form accessory corpora luteawhich regress by 7th month of pregnancy.

Pelvic ligaments

Relaxation of the pelvic ligaments. Caudal part of the sacrosciatic ligament is cordlike in the

non-pregnant but becomes more relaxed and flaccid asparturition approaches.

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Mammary gland development

Development of mammary gland starts before puberty.

During puberty, cyclic ovarian activity results in the productionof E2 and P4 .

During 1st

half of pregnancy, cellular proliferation of themammary duct and alveoli occurs under the influence of thesteroid hormones, P4 and E2 from ovaries and placenta.

By 5th month of pregnancy, growth of secretory tissue is nearly

completed.

By the end of pregnancy, stromal tissue is changed to alveolarcells that actively secretes milk.

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Pregnancy diagnosis

Rectal palpation

Hormonal measurement

Early pregnancy-associated protein

Ultrasound examination

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Location of pregnant uterus

In heifers Lies in pelvic cavity until 3-4 months of pregnancy.

In older cows Non-pregnant uterus lies on or over the pelvic brim.

Drops into abdomen even before 2 months of pregnancy.

In all ages of animals Uterus lies on the floor of the abdominal cavity after the 4th

month of pregnancy. By 5th-6th months of pregnancy, uterus is drawn well forward and

downward in the abdominal cavity, so that only the cervix anduterine vessels are palpated per rectum.

By 6th-7th months, fetus is large enough to be palpated perrectum.

By 8th-9th months, fetal nose and feet are palpated.

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During the normal course of pregnancy, the decline in progesterone

begins one to two days prior to parturition.

Hormones of pregnancy

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Progesterone Promotes development of endometrial glands. Maintains uterine quiescence. Modify behaviour. Development of lobular alveolar growth.

Estrogen Primes tissues for progesterone

Epithelial proliferation Smooth muscle hypertrophy

Glycogen deposition Vascularization Uterine metabolism

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Gonadotropins

FSH

Only in mare (eCG) supports development offollicles for the formation of secondary CL.

LH

Maintenance of CL function.

Further supported by prolactin andchoriomammotropins.

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Relaxin

Low in early pregnancy

Unknown origin

Suspected placenta

Produced by regressing CL and placenta at the end

of pregnancy to relax pubic symphysis and pelvicligaments

Needs potentiation by estrogens

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Oxytocin

Triggers production of PGF2

Stimulates smooth muscle contractility Uterine motility

For sperm transport

For fetal expulsion

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Placentation

Placenta is an apposition or fusion of the fetalmembranes to the endometrium to permitphysiological exchange between fetus and mother.

It is attached to the embryo by a cord of blood vessel.

The size and functions of the placenta changecontinuously during the course of pregnancy and theorgan is eventually expelled.

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Fetal membranes of farm animals

Membrane Origin Functions

Yolk sac Early entodermal layer Vestigeal

Amnion Cavitation from inner cell

mass

Encloses fetus in fluid-filled

cavity

Allantois Diverticulum of hindgut Blood vessels connect fetalwith placental circulationFuses with chorion to formthe choriallantoicplacentation

Chorion Trophoblastic capsule ofblastocyst

Encloses embryo and otherfetal membranesIntimately associated withlining of uterus to formplacenta

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Types of placenta

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Abnormalities of pregnancy

Mummification

Maceration

Pyometra

Mucometra

Early embryonic death

HydrocephalusAbortion

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Abnormalities of pregnancy contd

Fetal ascites

Fetal anasarca

Dropsy of fetus

Uterine torsion

Paraplegia

Premature birthProlonged gestation

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Abnormalities

Complete maceration of 6-7months

Aborted fetus Complete maceration of8th month

Llama placenta fetus umbilicus

torsion

Still birth, Abortion Mummification

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ReferencesArthur, G.H. 1997. Veterinary reproduction and

obsterics. The ELBS and Bailliere Tindall (4th Edition).

Hafez, E.S.E. 1997. Reproduction in farm animals. Lea

and Febiger Philadelphia (6th Edition). http://www.google.com.np/search?hl=en&biw=1280&

bih=666&tbm=isch&sa=1&q=pregnant%2Fanimals&btnG=Search

Robert, S.J. 1971. Veterinary obstetrics and genitaldiseases. CBS Publishers and Distributors, New Delhi(2nd Edition).

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DiscussionsWhat is pseudopregnancy?

Ans: Pseudopregnancy is the condition where animalshows signs and behaviour similar to the pregnant

animals when it is not pregnant in actual. It is morecommon in bitches. Bitch has very long metestrusperiod i.e. p4 level remains high for long period almostequal to the length of gestation. Due to this, bitch

shows the behavioural signs of pregnancy likeenlargement of teats, swollen abdomen etc. swollenabdomen may be due to accumulation of uterine milk.

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DiscussionsWhat is the difference between conception gestation

and pregnancy?

Ans : Conception is the onset of pregnancy, marked byimplantation of the blastocyst; the formation of aviable zygote where pregnancy and gestation are thesynonyms and it is the period from fertilization or

conception, to parturition or birth of the young.

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Discussions In which stage does hydrocephalous occurs?

Ans: Hydrocephalous is the condition where there isswelling of cranium due to accumulation of fluid inventricular system or between brain and dura. Itoccurs during the stage- period of fetus and fetalgrowth but the fluid increases in late gestation.

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DiscussionsWhat are the methods of pregnancy diagnosis?

Ans: Rectal palpation

Hormonal measurementEarly pregnancy-associated protein

Ultrasound examination

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Documents

Pregnancy and Its Duration