Sheep - AgRIS

7.3.4 Use of Hormone, Oestrus synchronisaffon and multiple ovulation
Oestrous cycle of the ewes is sypchronized so that a large number of them come in heat at
one time. This would help in reducing the cost of artificial insemination or natural breeding and
consequent care at lambing. Oestrous synchronization is also an integral part of embryo
transfer. However, the cost of the hormones used for the oestrous synchronization is prohibitive
under our conditions. It gives a uniform flock of lambs which will facilitate their disposal and
fetech more price. It can also gainfully be employed in breeding sheep in spring. In India,
although spring and autumn are technically peak breeding seasons, sheep can breed throughout
the year and synchronization can be done more cheaply by telescoping the breeding season.
The telescoping is done by introducing ram in the flock after keeping it away for 2 to 3 months;
70 to 80 per cent of ewes will come in heat in the very first oestrous cycle.
Synchronization of oestrous is initiated with the simultaneous administration, to the ewes,
of progestogen hormones or their analogues through feed, as implant or as impregnated vaginal
sponges. After the administration for 12 tol4 days the hormone is withdrawn. The animal
comes into heat within 3 days. Since the reproductive females are still under the influence of
the progestogen hormones the conception rate varies from 30 to 40 per cent whereas it varies
from 60 to 70 to 90 per cent during the subsequent cycle. Prostagladin F2 alpha or its synthetic
analogues, causing Iysis of corpus luteum, are also being used for the purpose. Two
intramuscular injections of 10 mg each at interval of 10 days bring all the animals in heat
within 72 hours.
7.3.5 Gestation period
The duration of gestation in native and cross bred ewes has been reviewed extensively by
Honmode (1970) and Kaushish (1971). The mean gestation length varies from 147 to 153 days.
The average gestation period varied from 151.2 to 152.2 days in Nali, Lohi and crosses
offormer with Mandya andNellore (Kaushish and Arora, 1974a). Ramamurti (1963), Singh et
al., (1977) and Kaushish et al., (1986) reported duration of estation in Native, Niligiri and
Bikaneri and Soviet Merino, respectively.
The gestation period is shorter for exotic than indigenous ewes (Sahani and Pant, 1978),
for ewes with exotic crossbred lambs, than those with indigenous lambs (Rao et al., 1978), for
lambs with ligher birth weights (Kishore et al., 1980) and for female than male lambs
(Narayanaswamy et al., 1975). The gestation is positively related with weight at service
(Kaushish, 1989).
The effect of breed, birth weight, sex of lamb, birth weight of dam at service, pH of
amniotic fluid and post service gain in weight on gestation length has been studied by Ostgard,
(1957) and Kaushisha and Arora (1973, 1974a) . Gestation has been reported to have positive
correlation with pH of amniotic fluid and negative with post service gain in weight and weight
at service (Kaushish andArora, 1974a).
A study on post parturn estrous interval has been carried out by Rawal et al., (1986b) to
determine the effects of season and sex of lamb on this trait in Muzaffarnagari sheep. In the
single norrnal lambing, twin larnbing and abortions, gestation period averaged 137.4±4.82;
168.1±23.63 and 172.8±13.22 days, respectively. The sex of larnb did not have significant
effect on postpartum estrous interval in case of single births. Effect of season was also non
significant. One percent ewes came in heat within 60 days. The average post parturn estrous
interval following twin lambings and after abortions was abnorrnally long 28.2% ewes came in
heat within 151-180 days after abortions.
7.3.6 Pregnancy diagnosis
There are several ways by which pregnancy can be diagnosed in sheep. Some methods are
relatively simple. The failure of an ewe to return to estrous gives an indication that she is
pregnant.
Physical exarnination of ewes in late pregnancy is sirnple and quick. The lamb can be felt
by gently palpating the ewes abdomen.
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