Milk
contributes to subsistence food supplies and provides food in areas where other foods are often not available. Milk is
produce and can be trades for foods such as sorghun, millet, pulses and
vegetables.
In contrast to
this milk has played only a small parts in diets of people in some wetter areas
where tsetse flies are found and which have largely
excluded cattle, milk is used for daily home consumption and cash income.
Milk animal help
to utilized spare labour in off
peak seasons and increase the efficiency of
use of land, crop residues, by
products and fodder form fallow
land.
The mammary
gland will continue to secrete milk at the
maximum daily level if milk is removed regularly and as fully as possible at
each milking if milk is not removed, the rate of secretion will be reduced
because as milk is secreted into the alveolus
the epithelial cells secrete
against an increasing pressure.
Milk is
produced in the udder. Some animals like
ewe and goats have two teats
whereas cows have four udders .
see the diagram at page 4. Milk is produced after parturition of animal . Secretion of milk is a continuous process,
and milk is stored inside the udder until it is removed by suckling or milking .
If milk is not removed, secretion soon stops or when this pressure become too
great, the rate of secretion reduce secretion slow down and stops about 35
hours after the last milking. See the diagram
The best time to
milk is every 9 –10 hours, but this would require more than twice a day
milking. Milking three times a day produces 15-25% more milk
than twice a day milking but the labour cost and management inputs
required are usually to great. In
intensive systems an 11-13 hours split between milking is adopted. While in
pastoral system cattle are often only milked in the morning, but the young
suckles for parts of the rest of the 24 hours period, thus maintaining milk
secretion.
Milk let
down is controlled by the hormone oxytoxcin
which is reduced as reflex to natural stimuli: Milk let
down by the udder can be stimulated physically by pressure applied to the teats
or suckling by the young animals or by washing of the treats with damp cloth.
Beside the
contraction of the myoepithelial cell oxytocin also causes a dilatation of sphincter muscle closing
the teat canal.
Since the
secretion of milk is a continuous process, although its does not occur at a
constant rate immediately following milking pressure in the duct and alveoli is
at its lowest and secretion occurs at a constant rate. In hours following the
pressure increases owing accumulation of milk in the gland and the mammary gland
reaches approximately 40- mmHg, secretion ceases due to the closure of the
capillaries and fall in the blood flow.
·
If
milking is inefficient and slow, all the milk will not be let down and milked
out.
·
Normally, there is usually 15% of the total
volume remaining in the udder after let
down.
·
Incomplete milking reduces the long- term yield performance
·
The method of milking (by machine or hand) also
affects the amount of milk produces.
·
Restricted suckled animal have been observed to
produce more milk than animal which are
not sucked.
Short –term
stress due to noise, excitement painful
treatment and other disturbance can affect milk let down since the adrenalin
secretion inhibits milk let down. High environmental temperature causes stress.
At ambient
temperature over 24oc, milk yields may be affected due to lower food intake,
temperature control activity and behavioral responses, such as shade seeking
These can be
compensated for by adjusting feeding to
a low dry matter concentrate, time of feeding, night feeding and by the
provision of shade and the orientation of housing.
Under this
condition, whether this is due to decreased oxytocin out put or to reduced
mammary blood flow as a result of activation of
the sympathetic nervous system by adrenlin.
Failure to
get adequate milk ejection due to
constriction of the teat canal occurs in animals. Because of excessive retention of milk in the
udder, the lactation period of such animals may be shortened. Since the
condition is genetic such animal should be excluded from breeding.