Sheep - AgRIS

Estrogen in large quantities inhibits FSH secretion. PGF2 alpha from non pregnant
progesterone dominated endomettreum reaches ovary by a local route between day 14 and 15
and kills the corpus luteum. The progesterone level falls and FSH facilitates follicular growth
and quick estrogen production. The rising estrogen induces behavioural estrous and trigers a
release of an ovulation surge of LH on the days of estrous. Estrogen levels then decline but the
new corpus luteum starts progesterone production which rises during the next few days and is
sufficient to hold gonadotropin release to low level. On day 16 the corpus luteum is killed again
and the cycle is completed.
The courpus luteum is a temporary endocrine organ which func-tions for only a few days
in cycling non pregnant ewes and through-out the duration of pregnancy once the ewe becomes
pregnant. The corpora lutea of sheep reaches maximum size by days 3 and at this time it is
reddish pink. Corpora lutea becomes paler as dioestrous approaches and after day 14
degeneartion is rapid. because the es-trous cycle of the ewe is shorter, the corpora lutea of the
ewe are devoid of the lipochrome pigment, hence the lighter colour. The cir-culating levels of
progesterone in plasma during follicular and luleal phases are 0.25 and 3.7 ng/ml in ewe.
Factors affecting corpus luteum
In polyestrous domestic animals, corporalutea develop after ovulation and function for 14-
15 days unless pregnancy occurs to signal the corpora lutea to continue functioning. There
appears to be marked species differences in the control of corpora luteal function. The pituitary
is needed in most species to produce luteotropin at ovulation to form the corpus luteum. Nonpregnant
uterus produces a substance probably PGF 2 alpha which has a luteolytic influence
onthe corpus luteum. The luteolytic effect of uterus is dominant to hypophysical control of the
life of the corpus luteum in sheep. Presence of an embryo in the uterus will prevent luteolysis.
Researches have shown that an embryo must be present in the uterus by the 12th day of the
cycle in sheep if luteolysis is to be avoided. Luteal regression can be prevented in the ewe and
cow by uterine infections. Presence of intra uterine devices (IUD) shroten, the estrous cycles in
sheep and cow.
Estrous during pregnancy
Estrous in the pregnant ewes is associated with follicular growth, but ovulation, breeding
and conception may occur during an existing pregnancy which would lead to surperfoetation.
Estrous has been observed in pregnant ewes (Matter, 1974; Younis and Afifi 1979; Kandasamy
and Pant 1980, Sinha et al., 1980). It has been observed in first month of pregnancy. It is not
usually accompanied by ovulation (Wllliamaet la.,1956). There is afeararnong sheep farrners if
mating takes place abortion may result (Sinha et al., 1980).
7.3.3 Laproscopy and Intra Uterine Insemination
A modified laparoscope aided intrauterine insemination technique has been developed for
using frozen thawed semen. Ewes exhibiting heat are fasted overnight. They are restrained in a
locally fabricated cradle suitable to the body size of native sheep. Sedation is induced with 1/m
injection of 0.1 ml of 2% solution of Xylazine hydrochloride. The abdominal area adjacent to
the udder is sprayed with 70% alcohol solution and infiltrated with 4 ml of 2% ligocaine
hydrochloride. Ewes restrained in cradle are suspended in head-down position at an angle 45°
and two stab incisions are made using 10 mm dia trocar approximately 5-7 cms anterior to
udder and each side of midventral line. Through one trocar a laparoscope and through the other
puncture site. A pair of ataumatic Allis forceps are introduced. Uterine hom is grasped gently
with forceps and lifted upto puncture site to view from outside. Frozen amd thawed semen
straw is loaded in modified aspic and 0.1 ml semen is deposited in the anterior part of both the
horns. The two puncture sites are then sutured and ewes are let free for grazing. An overall
lambing rate of 44.4% has been achieved for two cycle insemination with this technique at
CSWRI, Avikanagar. For wider acceptance under field conditions attempt is being made to
deveFop a non-envasive and cost-effective transcerival insemination technique as an alternate
to laparoscope aided intrauterine insemination technique which is likely to improve the
efficiency of artificial insemination of sheep with frozen semen.
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