Sheep - AgRIS

7. 3. 8 Interlambing interval
It is the interval between two successive lambings. Normally, it varies between 7 and 12
months, but may be as long as 20 months also. Values in the literture of lambing interval give
flock means of 218 days for Morada Nova sheep (Teixeira et al., 1980) and 408 days for
Mandya sheep (Purushotam, 1978).
Long interlambing intervals may be due to long postpartum anestrous period, failure to
conceive, death of all embryos or abortion. Ewes which do not conceive for two successive
breeding seasons are culled under improved managemental conditions. Lambing interval
decreases with parity upto 4, suggesting that young ewes which are still growing take longer to
regain condition after lambing. Interlambing period is also affected by season, (Fall et al.,
1982).
Reducing interlambing interval
An 8 month of lambing interval is possible provided that nutrition and management are
satisfactory (Naude and Grant, 1979). Hormonal treatment can be used to stimulate estrous
where seasonal anestrous from photoperiod results (Fletcher et al., 1980).
The period between lambing and conception (closed service period) of poorly fed ewes is
baout 180 days if no hormonal treatment is given. Intensively fed West African Dwarf ewes
conceive at an average of 43 days after lambing (Berger and Ginisty, 1980). Estrous can be
induced by using intravaginal sponges as early as 17 days after lambing (Nie Kerk, 1979).
Honmode et al., 1971a) induced heat in local Malpura ewes by inserting sponges 30 days after
lambing interval to 6 months (Brown et al., 1972).
Sheep loose weight if bred frequently (Sahni and Tiwari, 1974b). A seasonal production on
lambs results in high lamb mortality (Labban and Ghali, 1969) and poor growth rate
(Ganesakale, 1975).
7.3.9 Embryo transfer technology
Embryo transfer technology in sheep has been developing since last 3-4 decades and a
great deal of research is involved to simplify the technology and to refine the protocol. This
technology embraces a sequence of procedural events like oestrous synchronisation,
superovulation, embryo collection, evaluation, transfer, and freezing etc.
There has been little commercial embryo transfer activity in sheep as compared to cattle
mainly due to high cost and surgical procedures involved in the technology. However, during
the last decade, with the advent of laparoscopic procedures for intrauterine insemination,
embryo recovery and embryo transfer, it may be possible to invite attention of sheep industry
for substantial improvement of genetic make up through the use of embryo transfer technology
to increase the meat, milk and wool production.
This technology can be applied
1. To increase number of offspring from superior ewes.
2. To easy transporation of superior genes across the national and international boundaries.
3. To conserve the endangered breeds.
4. To produce exotic lambs from well adapted native surrogate mother.
5. To avoid risk of diseases while transporting live animal from outside and within the
country for breed improvement programme.
6. To produce lambs of desired sex.
7. Production of identical twms, Chimeras etc.
Donor ewes are selected on the basis of their genetic merit. Donor and recipients ewes
should have high fertility and free from any disease. A close synchrony of oestrous in donor
and recipient is an important factor influencing the success in embryo transfer. Oestrus in ewes
can be synchronised either by lengthening of progesterone phase of cycle (luteal phase) or by
shortening of progesterone phase. The former is achieved by administering progesterone in
body of ewe by means of daily progesterone feeding or intra-muscular injection, vaginal
sponges, subcutaneous implants and controlled internal drug releasing device (CIDR). Sponges
impregnated with 0.35 g of progesterone kept for 12 days in~situ vagina can bring the ewes in
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