Sheep - AgRIS

7. Reproduction
Reproduction, a normal physiological process, is one, of the most remarkable and imprtant
phenomena for the sheep husbandry and breeding. Regular and repeated reproduction is the
basis of the income from sheep. This is true not only of sheep but of other livestock; indeed, it
is true of the whole realm of agriculture. Reproduction is not only the source of continuing
income; it is upon this function that the whole science of genetics is based. As new animals are
produced, it is possible to influence the fundamental characteristics of some of the members of
the species. Influential as the reproductive function is, it is in turn influenced by other factors,
particularly age, health, and nutrition. Some other features of environment may also be
important in relation to reproduction.
There are many erroneous notions regarding the processes of reproduction. The breeder
should have a sufficiently intimate knowledge of the anatomy and functions of the male and
female reproductive systems to enable them to understand the reproductive processes in the
management a flock. Without such knowledge and understanding, there are no basic principles
of guidance and no modern basis for the development of scientifically sound breeding
programs.
Sheep in tropics generally breed throughout the year. Rams of indigenous breeds donate
good quality semen under proper management conditons throughout the year. However, the
rams of temperate breeds if not protected from high temperature, high humidity and high solar
radiation will not produce good quality semen during hot dry and hot humid seasons. Females
of tropical breeds cycle throughout the year unlike the temperate breeds which are affected by
hours of day light and breed with declining day length. They come in heat in autumn from
August to November, although some may breed upto February. Indigenous breeds usually
breed during nutritionally better time of year, i.e. July to August, or immediately after the onset
of the monsoon. A small percentage of them also breed during March-April when they are
stubble grazed on harvested fields and supplemented with Acacia and Prosopis pods, and thus
get flushed. Sheep breed in different seasons depending upon the availability offeed. To some
extent breeding season is controlled by the sheep breeder on the basis of availability of feed
resources and physical environmental conditions prevailing both at breeding and lambing,
though the consideration would be more in case of lambing as extremes of weather will more
seriously affect lamb survival. The breeding should, therefore, be arranged in a manner that the
lambs are dropped when plenty of vegetation is available and weather conditions are mild.
7.1 Male reproduction
Although there are individual exceptions, most male in the exotic breeds reach the stage of
development at an age of approsimately 4 to 6 or 7 months, when reproduction is possible. The
sex organs of males are apparently fully developed by that time, and the so-called secondary
characteristics which are dependent upon the presence and functioning of these organs are very
noticeable.
Because the reproductive cells of the male, the sperm or spermato-zoa, are formed in the
testicles, the testicles are generally considered the primary organs of reproduction of the male.
In addition to the formation of sperm cells, a testicular secretion testosterone when absorbed by
the body causes the development of the secondary sexual characteristics. When these features
are very marked in an individual, he is described as masculine. Masculinity is in no way
associated with the transmission of any features such as color, length of fleece, or other factors
of the ram to his offspring. The well-developed, masculine features merely indicate an
abundance of the hormone which stimulates the developrment of the features. The removal of
the testicles, and hence the removal of the source of the hormone, results in stopping the
development of the masculine characters. This is the reason. why wethers differ so much in
appearance from rams.
The testicles are normally carried outside the body cavity in a sac called the scrotum. The
normal temperature of the testicles is below that of the body. One of the main functions of the
scrotum is to regulate the temperature of these organs. This explains the lack of fertility in rams
if the testicles are not descended into the scrotal sac. It also explains why some rams that have
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