Sheep - AgRIS

oestrus during breeding seasons. An additional treatment of pregnant mare serum
gonadotrophin (200 IU) on day of sponge removal is required in acyclic ewes.
Corpus luteum, a source of progesterone, is sensitive to prostaglandin PGF2alpha. Two
intramuscular injections of PGF alpha 8-11 days apart can bring most of the treated ewes in
heat within 48 hours of last treatment. A protocol for oestrus synchronisation in donor and
recipient ewes with two i/m injection of 10 mg prostaglandin F2 alpha is in practice.
Superovulation among donor ewes is induced with the use of gonadotrophin. Pregnant mare
serum gonadotrophine (PMSG) and follicle stimulating hormone (FSH) from porcine, equine
and ovine origin, are most frequently used for superovulation. In general, qonadotrophins are
administered in multiple doses to female whose cycle is controlled by using progesterone or
PGF2 alpha. Recent attempts to increase the superovulation in donors have included the use of
gonadotrophin releasing hormone (GnRH), a combination of PMSG and FSH and sroqesterone
prinunq.
Ewes treated for superovulation are either mated with a proven fertile ram 2-4 times at 12 h
interval or subjected to A.I. with fresh diluted semen. Superovulation is known to impair the
sperm transport through cervix and decreases the sperm viability after natural mating. In order
to obviate problem of sperm transport, semen is directly deposited into uterus. Laparoscope
aided intrauterine insemination with fresh diluted semen generally result in high fertilization
rate in superovulated ewes.
Different methods of embryo collection and transfer have been attempted. These include a)
surgical and b) laparoscope aided nonsurgical procedures. In surgical procedures, reproductive
tract is exteriorized for embryo collection and transfer. This leads to surgical trauma and
formation of post-operative adhension and therefore, limit the repeated embryo collection
and/or transfer. Laparoscope aided procedures have opened the possibilities of repeated embryo
collection and transfer in sheep.
Quality of embryos are adjudged under stereozoom microscope according to uniformity of
zona cell shape and size, perivitelline space, vacuoles and cytoplasmic granules.
Depending upon age and number of cells, the good quality embryos are transferred in
oviduct (< 3 days old), near uterotubal junction (days 34) or in uterine body (days 5A6).
Embryos can be stored in phosphate buffer saline for few hours at 20°C or in
refrigerator at 5°C and liquid nitrogen for many days. Cryopreservation of emhryos has
become an integral part of embryo transfer and programme related to conservation of
germplasm. The transportation of germplasm resources as embryos rather than live
animals is cheaper, posses less risk of disease transmission and has added advantage of
allowing exotic stocks to develop in recipients well adapted to local conditions.
Procedures that are currently used for cryopreservation of sheep embryos either rely on
slow rates of freezing or direct transfer of embryos from room temperature to liquid
nitrogen i.e. vitrification. Results of survivability of frozen thaw embryos in general
varies from 35-73% depending upon freezing protocol, cryoprotectant, method
ofthawing, age and quality of embryos.
7.3.10 In vitro Fertilization
In-vitro production of embryos is a multistep process and include the techniques of In
vitro maturation and fertilization of oocytes and In-vitro culture of embryos. In recent
past technology of In-vitro production of embryos have developed and birth of lambs
are reported. Oocytes are generally recovered from slaughter house ovaries or from live
animals using laparoscope aided follicular aspiration/folliculocentesis.
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