TERMINATION OF PREGNANCY IN FARM ANIMALS
By Dr.Amit Bhardwaj,Large &Small animal surgery expert,Pune
INDICATIONS:
• Therapeutic abortion may be indicated during normal or abnormal pregnancy.
During normal gestation
• Misidentification of a breeding female
• Accidental breeding of a very young heifer, and
• Unwanted pregnancy in feedlot heifers.
During abnormal gestation
• Fetal maceration,
• Fetal mummification
• Hydramnios, and hydrallantois.
PHYSIOLOGY OF PREGNANCY MAINTENANCE:
• Gestation period extends from 270 to 292 days after breeding.
• Once conception has occurred, progesterone is essential for pregnancy maintenance.
• Both luteal and extraovarian sources of progesterone must be eliminated for successful induction of abortion.
• Although the maternal endocrine events of the first 15 days of cycle and of pregnancy are similar, the conceptus secretes a range of products, including steroids, prostaglandins, and proteins, beginning at 12 to 13 days of gestation.
• At least one of these products, interferon results in maternal recognition of pregnancy by inhibition of luteolysis and prolonged luteal lifespan.
• These effects are mediated by attenuation of endogenous prostaglandin F2 alpha (PGF2α) secretion.
• The functional life of the corpus luteum (CL) is controlled by a balance of luteotropic factors, including luteinizing hormone, and luteolytic factors, including PGF2α.
• PGF2α is the naturally occurring luteolysin, acting both directly and indirectly on the CL.
• PGF2α may cause local vasoconstriction of luteal blood flow; however, PGF2α, receptors are present on luteal cells, and PGF2α has a direct effect on luteal progesterone secretion.
• Endogenous luteolysis occurs in response to a cascade of hormonal events that result in pulsatile PGF2α secretion. It has been proposed that as a part of this cascade, oestradiol induces oxytocin receptors on endometrial cells.
• Oxytocin activates those receptors, resulting in the synthesis and secretion of PGF2α.
Role of Progesterone
• Throughout gestation: Fluctuate between 6 and 15 ng/mL
• Two to four weeks preceding parturition: A gradual decline.
• The adrenal gland may contribute 1- 4 ng/mL of progesterone.
• Progesterone is luteal in origin for the first 150 days of gestation.
• Between 150 and 250 days, the placenta acts as additional source of progesterone.
• In the final month of gestation, placental progesterone declines and pregnancy is again dependent on luteal progesterone.
• Successful treatment to induce abortion must lower circulating progesterone below 1 ng/mL, which is the threshold necessary to maintain pregnancy, and must be directed specifically at the source of progesterone appropriate for the stage of gestation at the time of treatment.
PROSTAGLANDIN F2 ALPHA:
• The corpus luteum (CL) is sensitive to PGF2α beginning 5 to 7 days after ovulation.
• In both normal and abnormal pregnancy, administration of PGF2α after that time results in luteolysis at any stage of pregnancy; however, PGF2α treatment alone induces abortion only up to 5 months of gestation.
• Rarely, luteolysis is incomplete, in which case luteal progesterone remains above the threshold, and partial cervical dilation and abdominal straining may occur before the cow resumes normal gestation.
GLUCOCORTICOIDS:
• Reduce placental progesterone secretion from 150 days of gestation. Luteal progesterone is unaffected, however, and abortion does not result from glucocorticoid treatment until the last month of gestation.
• During the final month of gestation, glucocorticoids act at the fetoplacental unit to increase the production of oestradiol and PGF2α, resulting in induced parturition.
• A combination of PG and glucocorticoids will induce abortion from 150 days of gestation.
ESTROGENS:
• During the first 2 to 3 days after ovulation, administration of estrogens alters oviductal transport of the bovine embryo and terminates pregnancy.
• After corpus luteum formation, estrogens cause luteolysis by inducing the endogenous PGF2α luteolytic cascade from the endometrium.
• The endometrium must be intact for estrogens to induce abortion.
• Estrogen is an exogenous luteolysin with unknown effects on the feto-placental unit; therefore, abortion can be induced reliably at up to 150 days of gestation.
• Administration of 30mg estradiol valerate, alone or in combination with dexamethasone in cows between 200 and 220 days of gestation has not been shown to decrease serum progesterone or result in abortion.
• Treatment with estradiol or its synthetic derivatives results in prolonged estrus behaviour, vulvar swelling, mucopurulent discharge, and relaxation of parts of the posterior reproductive tract.
• The function of the utero-tubal junction as a sphincter may be impaired, possibly allowing ascending infection and salpingitis.
• Time to return to fertile oestrus after estrogen treatment may be longer than after prostaglandin treatment.
OXYTOCIN:
• Treatment of cows with oxytocin from days 2 to 7 after oestrus with 100 to 200 IU of oxytocin prevents pregnancy, probably by preventing normal luteal development.
TERMINATION OF NORMAL PREGNANCY UP TO 150 DAYS:
Prostaglandins
• During first 5 months of pregnancy, treatment of choice is PGF2α or an analogue.
• Until 5 to 7 days after ovulation, cows do not respond. Later stages majority of cows respond by returning to fertile oestrus within 3-5 days of treatment. Cows not in oestrus within 5 days should be retreated.
• PGF2α or an analogue
o PGF2α : 25 mg IM
o Cloprostenol: 500 µg IM
o Fenprostalene: 1 mg SC
Oxytocin
• First few days after ovulation may prevent the establishment of pregnancy.
Intrauterine infusion of irritating solutions
• Between days 5 and 10 after ovulation, prevents the establishment of pregnancy and may cause luteolysis and early return to oestrus.
• Later than 11 days after ovulation occasionally lengthens the oestrous cycle.
• Up to 90 days of gestation, causes embryonic death necessitating manual evacuation of uterine contents.
• Suitable solutions
o Aqueous iodine 0.5%
o Tetracycline 2 Gm in saline.
Oestrogens
• Administration within 72 h of ovulation impedes oviductal transit of embryos.
• Up to 5 months of gestation, administration of an oestradiol ester, such as oestradiol valerate, results in abortion within 7 days. Occasional abortions occur up to 14 days after treatment.
• Oestradiol should be administered every 4 days until abortion.
o Diethylstilesterol: 40-80 mg IM
o Oestradiol ester: 4-8 mg IM
Manual techniques
Manual enucleation of the CL
• By transrectal manipulation manual enucleation of CL removes progesterone support for pregnancy and results in abortion at up to 150 days. Conceptus will be aborted in 2-5 days late or resorbed.
• Procedure:
o Per rectum grasp the prominent CL
o Express between the index finger and thumb
o Drop the CL in to the abdominal cavity
o Arrest bleeding by manual compression for 3-5 minutes
• Limitations
o Induce adhesions of the ovary and ovarian bursa and,
o Occasionally, severe hemorrhage, sometimes fatal.
Manual rupture of the amniotic vesicle
• By transrectal manipulation it is possible to manually rupture once the vesicle can be palpated at 30 to 35 days of gestation.
• After 60 days and up to 120 days of gestation, when the amniotic vesicle can no longer be isolated within the fluid-filled chorioallantois, it may be possible to terminate pregnancy by manual decapitation of the fetus.
• The mean time to abortion is 25 days, but abortion may occur up to 8 weeks after treatment.
TERMINATION OF NORMAL PREGNANCY AFTER 150 DAYS:
• In feedlot heifers, unwanted pregnancy leads to financial loss due to
o Reduced feed conversion
o Lower carcass prices, and
o Periparturient diseases including dystocia.
• Heifers should be examined on arrival at the feedlot to select appropriate candidates.
• Between 5 and 8 months of gestation, a combination of PGF2α and dexamethasone is necessary to remove both luteal and extraovarian sources of progesterone.
• All pregnant feedlot heifers are routinely treated with the combination of PGF2α and dexamethasone (Preferred combination to all other treatments), regardless of their stage of gestation.
o Inj.PGF2α : 25 mg IM
o Inj. Dexamethasone: 25 mg IM
• Abortion will occur reliably, with a mean time to abortion of 5 days.
• Abortion may be preceded or accompanied by oestrus behavior for duration of 9-12 h. Approximately 95% effective, although repeat treatments occasionally are necessary.
• Progestin-containing growth promotants should not be used until after abortion has been induced, as it may interfere with treatment.
• All heifers should be examined after treatment. Those still pregnant usually will respond to a second treatment.
• In the final month of pregnancy, either dexamethasone or prostaglandin alone induces premature parturition within 2-3 days
SEQUELAE:
• Approximately 80% incidence of retained fetal membranes after the fourth month of gestation. Majority of cases expel the placenta within 7 days without treatment.
• Fetal mummification develops in 2-4% of pregnant feedlot heifers treated with a combination of PGF2α and dexamethasone.
• In some cows, metritis or pyometra will develop after induced abortion; however, acute toxic metritis is an unusual sequelae.
IN HYDRALLANTOIS AND HYDRAMNIOS:
• Pregnancy can be terminated within 48 h in cows with simultaneous administration of PGF2α and dexamethasone, using doses recommended for normal pregnancy.
• Supportive treatment is necessary to compensate fluid loss.
• Parturition usually is abnormal.
• C-section may be an alternative to induced parturition.
IN FETAL MUMMIFICATION:
PGF2α or an analogue
• Therapeutic agent of choice.
• Excellent prognosis for return to fertility within 1-3 months.
• Expulsion of the fetus usually occurs within 24-72 h.
• Retreatment of cows with mummified fetuses still present at reexamination occasionally is necessary.
Oestrogens
• Luteolytic doses of estrogen also results in expulsion of mummified fetuses.
• Repeated treatments may be necessary at 48 h intervals.
• After treatment, the mummified fetus may become lodged in the vagina, requiring lubrication and manual removal.
IN FETAL MACERATION:
• Response to treatment with PGF2α or oestrogen is unrewarding.
• Macerated bones may be removed at surgery or through a partially dilated cervix, before or after administration of PGF2α or oestradiol however, endometrial damage carries a poor prognosis for return to fertility.
• In treating fetal maceration and mummification, glucocorticoids are ineffective because an intact feto-placental unit is necessary for their mode of action.
INDUCED PARTURATION AND TERMINATION OF PREGANANCY IN ANIMALS
Reference: Source-Professor P. sridevi & Professor S. Balsubraminian
