SIGNIFICANCE OF LITTER SIZE, DURATION OF DRY PERIOD AND STAGE OF PREGNACY ON
MILK YIELD AND COMPOSITION IN DAIRY ANIMALS

SIGNIFICANCE OF LITTER SIZE, DURATION OF DRY PERIOD AND STAGE OF PREGNACY ON
MILK YIELD AND COMPOSITION IN DAIRY ANIMALS

ASSAN, N

The factors influencing the amount and composition of
produced milk can be divided into two groups, namely internal
and external factors. This is very important to remember when
evaluating the milk quality and in the improvement of milk yield
and composition in a dairy enterprise. Of the external factors it
is possible to mention a few, litter size, duration of dry period
and stage of pregnancy. The present discussion explores the
significance of litter size, duration of dry period and pregnancy
on milk yield and composition in dairy production. In goats and
sheep dams bearing twins or triplets had higher milk yield than
single bearing dams, and this significant increase in milk
production in these dams that carried twins and triplets was
followed by an increase in lactation length. Due to the amount
of milk animal produce, the drying-off process is often more
complicated for dairy animals (cattle, goats and some sheep).
However, this period is essential to enables dams to regain the
body condition needed to support the subsequent pregnancy
and lactation. The majority of dairy animals dry off
spontaneously because of the aforementioned natural decrease
in daily milk production. The length of dry period influences
milk production in the subsquent lactation, with shortening of
the dry period showing a markedly negative effect on milk
performance of dams. Lactating animals should have an opportunity to rest and regenerate mammary tissue between
lactations. For optimal dairy animal performance in the next
lactation, lactating animals should have an opportunity to rest
and regenerate mammary tissue between lactations. The
amount of produced milk and its composition are influenced by
the stage of pregnancy, in the first half of pregnancy it is not
possible to observe any pronounced changes while in the
second stage of pregnancy can observe a gradual decrease in
milk production as well as an imcrease in levels of individual
milk components. During pregnancy and the first few days
postpartum, milk supply is hormonally driven – this is called the
endocrine control system. This implies that in the course of
lactation, changes in milk production are caused by changes in
activities of the endocrine system that are caused by hormones
sectreted by pitiutary gland (hypophysis cerebi) and placenta.
During the latter part of pregnancy, the mammary gland is
making colostrum, but high levels of progesterone inhibit milk
secretion resulting reduced milk yield. Progesterone influences
the growth in size of alveoli and lobes; high levels of
progesterone inhibit lactation before birth. Progesterone levels
drop after birth; this triggers the onset of copious milk
production. Estrogen stimulates the milk duct system to grow
and differentiate. Like progesterone, high levels of estrogen
also inhibit lactation, while the hormone prolactin must be
present for milk synthesis to occur.

Scientific Journal of Review

2014