Sheep - AgRIS

7. 2 Types of breeding
Sheep are bred either by natural mating or through artificial breeding. Rams of the
Indigenous breeds donate good quality semen under proper management conditions throughout
the year. However the rams oftemperate breeds if not protected from high temperateure, high
humidity and high solar radiation will not produce good quality semen during hot dry and hot
humid seasons. Females oftropical breeds cycle throughout the year. Temperate breeds which
are affected by hours of day light, breed with declining day length. They came in heat in
autumn from August to November, although some may breed up to February.
7. 2.1 Natural Breeding
The natural breeding is done either by flock mating, per mating and hand mating. In flock
mating system>/8heep can be bred naturally or through artificial insemination. The natural
breeding is done by either flock mating, pen mating or hand mating. In flock-mating system,
breeding rams are usually turned out in the flock during the mating season at the rate of 2 to 3
per cent of the ewes all through day and night. It is most widely practised in the flocks of all
farmers. Semi flock breeding or pen breeding is done to conserve the energy of rams and give
them rest. In this, the rams are turned out for service with the flock in the pen during night, and
confined and stall-fed or grazed separately during the day time. Hand mating is practised when
exotic purebred sires are used, or when it is considered desirable to extend the services of ram
over much larger flocks. Sheep in heat do not manifest behavoioural symptoms. Hence, the
teaser rams are employed for detecting the ewes in heat. These ewes are then taken out of the
flocks and bred to the designated sire of the flock. In pen and hand-mating systems and when
teaser rams are used for heat detection some dye mixed in grease or simple linseed oil is
smeared on the brisket of the ram. This makes it possible to record the date when the ewes is
bred and also to remove them from the breeding flock. The colour of the dye should be changed
every 16 to 18 days so that the repeaters can be discovered, if the bred ewes have not been
removed from the flock. This is termed as marking of ewes by breeding ram and marked ewes
are considered as bred. Breeding rams are usually turned out in the flock during the mating
season at the rate of 2 to 3 per cent of the ewes all through day and night. It is most widely
practised in the flocks of all farmers.
7. 2.2 Artificial insemination
From four to eight ewes may be inseminated from one service of a ram—although as many
as 30 to 40 have been reported, 0.1 to 0.2 cc of semen is sufficient for the purpose when there is
a heavy concentration of sperm in the semen. Great numbers of sperm are of course needed as
they are microscopic in size, and the reproductive tract of the female through which they must
migrate to come in contact with the egg, also microscopic, is very large indeed in relation to the
size of the reproductive cells. Apparently, most sperm do not survive more than 18 to 24 hours
in the reproduction tract of the ewe. Russian research workers have reported impregnating from
300 to 400 ewes in one season with the semen collected from a single ram. They also reported
that 90 percent of the ewes so insemianted became pregnant. This is a far greater number than
could be bred to one ram using natural methods. From 40 to 60 ewes is generally considered a
reasonable for a ram in one season.
For the purpose of artificial insemination, artificial vaginas are used for the collection of
the semen, although it may be recovered in some quanitity from the vagina of an ewe. Semen
can be preserved for several days with suitable media and low temperature and has been
transported long distances and used successfully in experimental tests. The semen is diluted for
use and is injected into the vagina or deposited at the base of the cervix through a glass or
plastic tube. Two inseminations at about a 12 hour interval, beginning soon after the onset of
heat, are often recommended.
Although little use has been made of artificial insemination in sheep except in an
experimental way, some of the advantages and disadvantages are known. The chief advantages
are: the usefulness of a superior sire may be extended; the number of rams needed for a large
flock is reduced, and a flock of considerably greater uniformity should result. Disadvantages
include the need for extra equipment and labor, some of which must be skilled in the work the
399