Sheep - AgRIS

7. 3.1 Puberty
Puberty in the female is exhibited by the first estrous. The breed of the ewe affects the age
and weight at puberty and sexual maturity. Ewe lambs in most of the mutton breeds reach
puberty at the age of 10-12 months normally breeding during the first autumn. Larger, slower
maturing breeds may mature at the age of 18-20 months.
Awassi lambs on a good diet first display estrous at an average age of 274 days (Younis et
al., 1978), but Rambouillet crossbred lambs in Rajasthan are about 615 days old before they
display estrous (Kishore et al., 1982). This difference is largely due to the different growth rates
resulting from different nutrition. The average age at puberty in Ossimi and Barki ewe lambs
reared on high plane of nutrition was 347 days in Egypt whereas, it was 366 days on a low
plane of nutrition (Ei-Homosi and El-Hafiz, 1982). The variation in age at puberty occurs in
sub-tropics where the ewes are reasonably anestrous so that if a lamb fails to cycle in her first
season she will not cycle until the next, several months later.
Under Indian conditions, the ewes reach sexual maturity at 9 to 14 months of age,
however, the full body growth is only attained between 18 to 24 months of age and the stage at
which the mating is performed. Merino sheep mature more slowly than the Hampshire or
Suffolk breeds, crossbred lambs generally mature earlier than pure bred lambs. Roy et al.,
(1962) recorded first estrous in young Bikaneri ewes of less than one year of age. Majority of
the Nellore ewes attained puberty at 630-810 days of age (Gupta et al., 1987). The age at
puberty has been reported to vary from 306-383 days in different exotic breeds (Martemucci et
al., 1983).
7. 3.2 The Estrous Cycle
Rhythmic sexual behaviour patterns develop in females during puberty. This change in
behaviour in called estrous and it occurs with each estrous cycle in non seasonal breeders
unless pregnancy intervenes. The combination of physiological events which begin at one
estrous period and end at the next is termed as estrus cycle.
Estrous occurs every 14-19 days with a mean of 17 days (Terrill, 1974). Similar duration
has been observed for ewes in tropics by Narayanaswamy and Balaine (1976); Gaillard (1979)
and Yenekoye etal., (1981). Cyclelengthsofupto 70 dayswererecordedforFulani ewes in Niger
by Yenikoye et al. (1982).
Visual signs of approaching estrous are, a swelling and redness of the vulva and
restlessness or nervousness indicating a desire for company, but the most abvious sign is
ridding and inturn being ridden. The breeding occurs only during estrous although the ram is
capable of breeding at any time (Dhanda, 1970).
Three types of estrous cycles commonly observed are:
1) One type is seen in sheep, goat, cow and sow during breeding seasons. The infertile cycle
in these species culminates in spontaneous ovulation of mature follicles; corporalutea
automatically formed, becomes functional and exists for a definite period oftime.
2) Rat and mouse are example of another type of estrous cycle in which ovulation is
spontaneous, but the corpus leuteum which is formed is not functional unless mating
occurs.
3) In third type maturation and ovulation of follicles fail unless the male copulates with the
female, Rabbit is an induced ovulator.
The main events of the estrous cycle of the ewe can be divided into those associated with
the growth of follicle and those associated with the growth of the corpus luteum. The growth of
the follicles takes place during proestrous and estrous. The period of the corpus luteum can be
divided into two periods, metestrous and diestrous. The estrous cycle is usually dated from the
first day of estrous.
1. Estrous
Estrous is defined as the period of sexual receptivity during which ovulation occurs in most
species and the corpus luteum begins to form. The psychic estrous is brought about by the
action of estradiol on the central nervous system. Symptoms of heat are less pronounced in ewe
than in cow or mare. The ewe in heat makes little effort to tease and mount. Because of weak
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