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.
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. See the diagram iii at pg 4.
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.