MILK
PRODUCTION AN HYGIENE IN RWANDA
By NZABUHERAHEZA François Dominicus
1. INTRODUCTION
Rwanda is a highland country located in central Africa. It is bordered
on the north by Uganda, south by Burundi, east by Tanzania and west
by the Democratic Republic of Congo. Because it is one of the world’s
most densely populated nations, its land is intensively cultivated
to feed its people. Rwanda has scenic beauties including several
animal sanctuaries. Volcanoes National Park, one of the most beautiful
sights in Africa, is located 60 miles northwest of the capital Kigali.
It is home to many gorillas and several bird species. Akagera National
Park is located in north-eastern Rwanda and surrounded by wooded
hills, river line forest, and grassland, as home to lions, elephants,
hippos, impalas, zebras, buffaloes, and other animals. Other game
reserves include Nyungwe Forest Reserve and the Biosphere Reserve
[1].
There are four different seasons in Rwanda. Long rains prevail from
mid-March to mid-May, while the short rains last from mid-May to
mid-October through mid-December. The long dry-season goes from
mid-May to mid-October, and the short dry season is from mid-December
to mid-March. Average temperatures range between 60 and 90 degrees
Fahrenheit. Mostly farming and foreign aid sustain the Rwanda economy.
Its agricultural sector, producing mainly tea and coffee, accounts
for about 90 per cent of the country's exports. There are also several
industries making, among other things, soap and plastics. Natural
resources include tin, gold, tungsten, hydropower and natural gas.
Agriculture is the mainstay of the Rwandan economy employing over
94% of the active population and contributing 43% of the GDP and
8% of the export earnings. The per capita annual income is USD 251
and more than 65% of the people live below the poverty line. Agricultural
production, however, is rudimentary leading to food insecurity and
chronic rural poverty. The problem is aggravated by lack of post-harvest
and agro-processing technologies, leading to unacceptable losses,
lack of value-adding and failure to provide the much-needed rural
employment [1].
Though agriculture is the leading sector and major source of future
growth in the Rwandan economy, the manufacturing sector in Rwanda
currently accounts for less than 8% of the total economic output.
Besides its rich agricultural resource endowment, the Rwandan food
Industry processes far less than 1% of the available raw materials
including milk, meat, egg and fish. Livestock and fisheries have
great potential to contribute to the country's food security and
economy and contribute to improve the nutritional value of food.
Almost all the livestock and their fresh products (milk, meat, egg,
etc) are locally consumed and the demand has continued to rise in
the last twelve years after war, due to the general improvement
of national economy. Milk processing is in an embryonic state while
there are a few dairy plants like Nyabisindu, Rubilizi, Inyange,
Gishwati and Umutara. The milk products are natural traditional
fermented milk, lactic fermented milk, butter, cheese and yoghurt,
all of which are very delicious and nutritional [1].
2. THE ORIGIN OF RWANDAN COW'S MILK PRODUCTION
Practically everywhere on earth man started domesticating animals.
In Rwanda, milk has been an important food for man since the domestication
of cattle and the adoption of pastoralist agriculture. The dairy
animals (Ankolé, N'dama, Sahiwal, Jersey, Frisonne, Brune
des Alpes) of today have been developed from untamed animals which,
through thousands of years, lived different altitudes and latitudes
exposed to natural and, many times, severe and extreme conditions.
The people of Rwanda know the economic importance of milk production.
It is also the most versatile of the animal-derived food commodities
and is a component of the diet in many forms. In addition to milk
itself, a rural technology evolved which permitted the manufacture
of traditional fermented milk (Ikivuguto), traditional butter (Ikimuri)
using traditional churner (gourd: igisabo) and butter milk. As a
rule, herbivorous, multipurpose animals were chosen to satisfy this
need of milk, meat, clothing (Ingozi, inkanda, impuzu, inkosha,
ingobyi, ingoma). Herbivorous animals were chosen because they are
less dangerous and easier to handle than carnivorous ones [1].
3. MILKING
Milking is the removal of milk from the udder, which is achieved
when external forces such as suckling or milking open the teat duct
at its end. Lactation is the continuous secretion and storage of
milk in the udder. The milk ejection or reflex effect is short term,
inhibited by pain or fear, but stimulated by good husbandry practices.
Even so, at least 10% of secreted milk will be retained in the udder
as residual milk.
Milk intervals affect the amount of residual milk carryover between
milking. Equal intervals of 12 hours give highest lactation yields
but the effect of unequal intervals is small, up to 16 and 8 hours,
and can be minimized if the highest yielders are milked first in
the morning and last in the afternoon.
In Rwanda, dairy farmers with varying levels of skill, knowledge
and resources, maximize returns from milk production by influencing
lactation through selective breeding and control of reproduction,
nutrition, disease and general management. The methods of milking
have a particularly important effect because a cow cannot secrete
over a period, more milk, than is removed by milking. Thus, maximizing
milk removal in ways which are economic, will take full advantage
of secretion potential. However, the lactation includes both milk
secretion and storage in alveolar cells and ducts within the mammary
gland, followed by milk ejection (let-down) and milk removal. Milk
secretion is continuous and usually at a constant rate for at least
12 hours resulting in a gradual increase in internal udder pressure.
Milk ejection is a neuro-hormonal reflex initiated by various stimuli
when milking. These stimuli, which reflect good husbandry practices,
are either natural (inborn) or conditioned (learned by experience),
including, for example, feeding and udder preparation. They cause
the alveoli and small milk ducts to contract forcing milk towards
the udder sinus. Once this has happened, most but not all, of the
milk can be removed when external forces such as suckling or milking
open the streak canal (teat duct) at the teat end. At least 10%
will be retained in the udder as residual milk.
Concerning milking intervals, 10% and 20% of the secreted milk which
is not expressed from the secretary tissue and is retained in the
udder when milking is completed, is called residual milk and has
a much higher fat content than the end-of-milking stripping. The
quantity of residual milk is proportional to the total yield, so
that with unequal milking intervals there is a larger net carryover
of milk fat from the longer night-time to the shorter daytime interval.
This accounts for the apparent faster secretion rate and higher
fat content of afternoon milk production. Milk yields, particularly
from higher yielding cows, are usually greater when milking intervals
are 12 hourly. The effect of uneven intervals is not large up to
12 hours, and can be minimized by milking the higher yielder first
in the morning and last in the evening.
Milking frequency affects the total daily production. Milking three
times instead of twice daily raises milk yields by an average of
10%. The chemical composition of milk is unaffected [1].
Chemical composition of Rwandan cow's milk:
The chemical composition of a typical Rwandan’s cow is as
follows:
- Moisture: 87%
- Dry matter: 13%
- Proteins: 3.5%
- Non-protein nitrogen: 0.2%
- Lipids (fat): 4%
- Carbohydrates (Lactose): 4.5%
- Ash: 0.8%
Incomplete milking either from excessive amounts of residual milk
or end-of-milking stripping can be avoided by effective milk ejection
stimulation, and by efficient fast milking by hand or machine [1].
Milking frequency
As a general rule, herd lactation yields will rise as the frequency
of milking is increased. On average, the rise in milk yields will
be between 10% and 15%, the largest increases occurring among heifers.
The chemical composition of the milk (fat and solids-not-fat) will
be unaffected. Recent commercial data from developed dairy areas
(Nyabisindu, Rubilizi, Inyange, Umutara, Gishwati) also reveal that,
on average, up to 10% increase in yield is required to cover the
extra costs of milking, twice daily. The full benefit of the increased
frequency is obtained by milking three times daily throughout lactation,
rather than reverting to twice daily when milk yields begin to fall.
The reasons for the increase in lactation yields are inconclusive;
the most likely being the more frequent removal of secretion inhibiting
substances which begin the drying-off process [1].
Incomplete milking
There are two forms of incomplete milking.
One is that excessive amounts of residual milk are retained in the
udder because of inadequate milk ejection stimuli, or the inhibitory
effects of adrenalin secreted by cows becoming frightened and upset
during milking, or even by slow milk removal. The other form is
that some of the available milk is left in the udder when milking
ceases, ie the so-called stripping.
The modern milking machine is designed to remove 95% of available
milk without recourse to additional cluster weight or manual assistance.
Hand stripping, particularly with the finger and thumb, should be
avoided. The amounts of stripping are likely to be small, even in
relation to normal levels of residual milk and if not removed, are
unlikely to significantly affect either the lactation yield or quality
of milk. Milking routines are a reflection of good stockman ship.
Cows are creatures of habit; avoid any circumstances which upset
or frighten them and thus inhibit milk ejection.
Residual milk amounts will be inversely proportional to the strength
of the stimuli signals. Develop a regular and repetitive milking
routine. Make changes gently and carefully. Milk quickly and quietly
in a stress-free environment [1].
Milking routines
The aim of an efficient and effective milking routine is to leave
the least amount of residual milk in the udder. This, in itself,
is a measure of good stockman ship. Milk ejection can be stimulated
manually by a series of activities carried out by the person doing
the milking. The amount of residual milk is inversely proportional
to the strength of the conditioned stimuli signals, which are developed
into a regular, repetitive milking routine, including such activities
as feeding and udder preparation. The stimulation response is transitory,
the maximum effect declining within a few minutes of milk ejection
occurring.
Therefore, delayed milking will reduce the amount of milk removed.
The internal pressure of milk within the udder peaks between one
and two minutes after milk ejection, and hence milking should be
completed as soon as possible after this occurs. Cows are creatures
of habit and consequently changes to the routine should be made
gently and quietly. It is important to avoid any circumstances which
upset or frighten them causing the release of adrenalin which adversely
affects the circulatory and emasculatory systems, thus restricting
effective milk ejection and prolonging the milking duration. The
response of cows and those milking them to a pleasant and stress
free environment will be measured in terms of production levels
[1].
Because residual milk and stripping have fat percentages that normally
exceed 10%, incomplete or slow milking can reduce markedly the fat
content of the milk at any particular milking. However, it is important
to recognise that milk fat retained or left in the udder is not
lost but will be obtained at the succeeding milking. In fact, although
management factors (like varying milking intervals and milking frequency)
may alter the fat content of milk at one milking, the average fat
content over a period of time will be unaffected. On average, the
fat content of milk obtained must be the same as that secreted into
the udder. The concentrations of protein, lactose and other solids-not-fat
are unaffected by changes in milking management, either at one or
more milking.
In Rwanda, we hand milk with clean and dry hands. We use the full
hand to avoid finger and thumb stripping. Rear quarters should be
milked first as they contain most milk and the milking bucket hooded
to reduce contamination from dust and udder hairs [6].
However, in most developed countries, machine milking is done. Methods
of machine milking are designed to create a pleasant milking sensation
for the cows and to avoid any possible hazard to udder health. It
is most important that milking is done with a well designed, carefully
cleaned and properly maintained machine which is strictly operated
according to the manufacturer's instructions [2].
But the machine milking will only create a pleasant sensation for
the cows if the machine is kept clean, maintained properly and operated
according to the manufacturer’s instructions. Attach and remove
clusters carefully to avoid vacuum fluctuations which cause mastitis.
Readjust slipping teat cups and replace fallen clusters immediately
[2].
A skilled operator pays particular attention to careful cluster
attachment and removal from the udder. During cluster attachment
it is essential to ensure that the vacuum cut-off arrangements to
the claw piece are effective so that excessive volumes of air do
not enter and cause vacuum fluctuations in the main vacuum pipeline
system, as this could increase mastitis incidence. Attach each teat
cup carefully starting with the two furthest from the operator.
The clusters are removed as soon as milk flow ceases, avoiding excessive
air entry through the teat cups by cutting off the vacuum supply
before gently but firmly pulling the teat cups from the udder. During
milking, any teat cups which slip from the teats should be readjusted
immediately and any clusters which fall to the floor should be cleaned
and reattached without delay [3].
4. MILK HYGIENE
Exclude milk from clinical mastitis cases to avoid high bacterial
counts. Use mastitis control routines at each milking to reduce
the proportion of infected cows and clinical mastitis cases. Contamination
from dirty udders and teats can be avoided by good cow housing and
grazing management by permanent stipulation. Wash off visible dirt
from udders and teats prior to applying the hands.
If udder washing is necessary, then drying afterwards is essential.
Individual paper towels for both washing and drying are preferable
to udder cloths. Clean and disinfect milking and ancillary equipment
after use, paying particular attention to milk contact surfaces
which are a main source of contamination and adulteration. In Rwanda,
all dangerous diseases are detected and avoided by the veterinary
system of guards.
The milk secreted into an uninfected cow's udder is sterile. Invariably
it becomes contaminated during milking, cooling and storage, and
milk is an excellent medium for bacteria, yeasts and moulds that
are the common contaminants. Their rapid growth, particularly at
high ambient temperatures can cause marked deterioration, spoiling
the milk for liquid consumption or manufacture into dairy products.
This can be avoided by adopting the simple, basic rules of clean
milk production [4].
Udder infection
The essential requirements to maintain udders free from infection
(e.g. mastitis) are to manage cows so that their udders and teats
are clean; milk them in such a way that minimizes bacterial contamination;
store the milk in clean containers and, wherever possible, at temperatures
which discourage bacterial growth until collected. Simple and low-cost
husbandry practices enable milk to be produced with a bacterial
count of less than 50,000 per ml. When it comes to clean milk production,
prevention is better than cure.
It is impossible to prevent mastitis infection entirely but by adopting
practical routines, it can be kept at low levels. Most mastitis
is sub-clinical and although not readily detected by the stockman,
it will not normally raise the bacterial count of herd milk above
50,000 per ml. Once the clinical stage is reached, the count may
increase to several millions per ml and one infected quarter may
result in the milk from the whole herd being unacceptable. It is
important to detect clinical cases and exclude their milk from the
bulk.
Other sources of contamination
Under normal grazing conditions, cows' udders will appear clean
and therefore washing and drying will be unnecessary. Otherwise,
any visible dirt must be removed using clean, running water, individual
paper towels or cloths in clean water, to which a disinfectant has
been added (eg sodium hypochlorite at 300 ppm). If udder cloths
are used, provide a clean cloth for each cow. After each milking,
wash and disinfect them, and hang them up to dry. Disposable paper
towels are preferable and more effective for drying after washing.
When cows are housed or graze in heavily stocked paddocks, external
udder surfaces are usually grossly contaminated with bacteria even
when they appear visibly clean. Therefore, routine udder preparation
procedures should be followed. Whenever udders are washed they should
be dried.
Fore milking has little affect on the total bacterial count of the
milk, but is an effective way of detecting clinical symptoms of
mastitis. Filtering or straining the milk removes visible dirt but
not the bacteria in the milk, because they pass through the filter.
Aerial contamination of milk by bacteria is insignificant under
normal production conditions. The contact surfaces of milking and
cooling equipment are a main source of milk contamination and frequently,
the principal cause of consistently high bacterial counts. Simple,
inexpensive cleaning and disinfecting routines can virtually eliminate
this source of contamination [4].
Milking equipment must have smooth contact surfaces with minimal
joints and crevices. Renew rubber components at regular intervals.
Water for dairy use is either from approved, piped supply or chlorinated
(50 ppm) before use. In hard water areas, milking and ancillary
equipment must be de-scaled periodically.
Detergents are necessary to clean milking and ancillary equipment
effectively before disinfection. Effectiveness is increased with
solution temperature, concentration and time of application.
It is virtually impossible with practical cleaning systems to remove
all milk residues and deposits from the milk contact surfaces of
milking equipment. Except in very cold, dry weather, bacteria will
multiply on these surfaces during the interval between milking,
so that high numbers (e.g. 106 per m2) can be present on visually
clean equipment. A proven cleaning and disinfectant routine is required
so that with the minimum effort and expense, the equipment will
have low bacterial counts, as well as being visually clean.
The essential requirements are; use milking equipment with smooth
contact surfaces with minimal joints and crevices, an uncontaminated
water supply, detergents to remove deposits and milk residues and
a method of disinfection to kill bacteria.
Water supplies
Unless an approved piped supply is available, it must be assumed
that water is contaminated and therefore hypochlorite must be added
at the rate of 50 ppm to the cleaning water. Hard water (i.e. high
levels of dissolved calcium and other salts) will cause surface
deposits on equipment and reduce cleaning effectiveness. In such
cases, it is necessary to use de-scaling acids such as sulphamic
or phosphoric, periodically.
Detergents and disinfectants
Detergents increase the 'wetting' potential over the surfaces to
be cleaned, displace milk deposits, dissolve milk protein, emulsify
the fat and aid dirt removal. Detergent effectiveness is usually
increased with increasing water temperature, and by using the correct
concentration and time of application. Detergents contain inorganic
alkalis (e.g. sodium carbonate and silicates and tri-sodium phosphate),
surface-active agents (or wetting agents), sequestering (water-softening)
agents (e.g. polyphosphates) and acids for de-scaling. Many proprietary,
purpose-made detergents are usually available, but otherwise, an
inexpensive mixture can be made to give a concentration in solution
of 0.25% sodium carbonate (washing soda) and 0.05% polyphosphate
(Calgon). Disinfectants are required to destroy the bacteria remaining
and subsequently multiplying on the cleaned surfaces. The alternatives
are either heat applied as hot water or chemicals. Heat penetrates
deposits and crevices and kills bacteria, provided that correct
temperatures are maintained during disinfection. The effectiveness
of chemicals is increased with temperature, but even so, they do
not have the same penetration potential as heat and they will not
effectively disinfect milk contact surfaces which are difficult
to clean.
Disinfect milk contact surfaces with either hot water (85 °C
initial temperature) alone or with a chemical disinfectant.
Provide a dairy or suitable place for cleaning and disinfecting,
draining and storing milking and ancillary equipment which is not
cleaned and disinfected in-situ.
When hot water alone is used, it is best to begin the routine with
water at not less than 85 °C, so that a temperature of at least
77 °C can be maintained for at least 2 minutes. Many chemicals
are suitable disinfectants, some of them combined with detergents
(ie detergent-sterilizes). Use only those, which are approved, avoiding
particularly those which can taint milk (e.g. phenolic disinfectants).
Always follow the manufacturer’s instructions. Sodium hypochlorite
is an inexpensive example of an approved disinfectant suitable for
most dairy purposes. Sodium hydroxide (caustic soda) can also be
very effective at concentrations of 3%-5% at ambient temperatures,
provided adequate contact time is given with the surfaces to be
cleaned and disinfected [4].
Dairy disinfectants are sold as concentrates and in this form, are
often corrosive and damaging to the skin and eyes. They should always
be labelled, handled with care and stored out of reach of children.
They should not be mixed unless specific instructions are given
and disinfectant powders must be kept dry. If any concentrated detergent
and/or disinfectant come in contact with the skin or eyes, the affected
area should be washed immediately with copious amounts of clean
water. If acids are used they must always be added to the water,
not vice versa [4].
Clean and disinfect the ancillary equipment such as coolers, foremilk
cups and udder cloths effectively using hot detergent/disinfectant
solution.
Drain and store all the milking and ancillary equipment in a clean
place, such as the dairy.
The milking location
The milking location should be equipped with a piped hot and cold
water supply, a wash trough, brushes, a work surface, storage racks
and cupboards and, if necessary, a vacuum pipeline connection. In
addition, it is advisable to have a dairy thermometer (0 °C
– 100 °C), rubber gloves and goggles for use when handling
chemicals [4].
Daily routines for cleaning and disinfecting vary with the size
and complexity of the milking installation, but will include methods
of removing dirt and milk from the equipment followed by disinfection.
For hand milking, bucket and direct-to-can milking machines, basic
manual methods of cleaning and sterilizing are adequate and effective.
For pipeline milking machines, in-situ (in-place) systems are necessary.
Milk can become grossly contaminated from bacteria on ancillary
equipment, which must also be cleaned and disinfected effectively.
Coolers, either the corrugated surface or the turbine in-can, can
best be cleaned and disinfected manually and stored in the dairy
to drain [5].
Refrigerated bulk milk tanks can be cleaned either manually using
cold or warm detergent/disinfectant solutions or for the larger
tanks, by automatic, programmed equipment. In either case, a cold
water chlorinated (50 ppm) rinse precedes and follows the washing
solution. Foremilk cups can be a potent source of bacterial contamination
and need to be cleaned and disinfected after each milking. They
should then be stored in the dairy to drain.
It is important with any method of cleaning that the equipment is
drained as soon as possible after washing for storage between milking.
Bacteria will not multiply in dry conditions, but water lodged in
milking equipment will, in suitable temperatures, provide conditions
for massive bacterial multiplication. Equipment with poor milk contact
surfaces, crevices and large joint numbers, remaining wet between
milking in ambient temperatures above 20 °C, should receive
a disinfectant rinse (50 ppm available chlorine) before milking
begins.
5. MASTITS CONTROL AND THE INFECTION PATTERN IN DAIRY COWS
Mastitis is an inflammation of one or more quarters of the udder
usually caused by bacterial infection. Several types of bacteria
cause distinctly different mastitis infections. Most mastitis persists
as sub-clinical infections and is not detected. Only occasionally
are there clinical signs with clots in the milk and inflamed quarters.
Antibiotic infusions into the udder nearly always cure the clinical
disease but may not eliminate the bacterial infection. Mastitis
reduces milk yields, increases the cost of production and makes
milk less valuable for liquid consumption and manufacture.
Mastitis is an inflammation of the udder and is common in dairy
herds causing vital economic losses. It can not be eradicated but
can be reduced to low levels by good management of dairy cows. Of
the several causes of mastitis, only microbial infection is important.
Although bacteria, fungi, yeasts and possibly virus can cause udder
infection, the main agents are bacteria. The most common pathogens
are Staphylococcus aureus, Streptococcus agalactiae, Str. dysgalactiae,
Str. uberis and Escherichia coli though other pathogens can cause
occasional herd outbreaks. Mastitis occurs when the teats of cows
are exposed to pathogens which penetrate the teat duct and establish
an infection in one or more quarters within the udder. The course
of an infection varies; most commonly it persists for weeks or months
in a mild form which is not detected by the stockman (ie sub clinical
mastitis). With some pathogens, typically E coli, the infection
is frequently more acute and there is a general endotoxaemia with
raised body temperature, loss of appetite and the cow may die unless
supportive therapy is given. When clinical mastitis occurs the effective
therapy is a course of antibiotic infusions through the teat duct.
These nearly always remedy the clinical disease and often eliminate
the bacterial infection. Infections may spontaneously recover but
most persist to be eliminated eventually by antibiotic therapy or
when the cow is culled. The susceptibility of cows varies considerably
and new infections are most common in older cows during early lactation,
at the start of the dry period and when the management is poor.
Mastitis causes direct economic losses to farmers in several ways;
milk yields are reduced, milk that is abnormal or contaminated with
antibiotics cannot be sold, high veterinary and antibiotic costs,
a higher culling rate and occasional fatalities. The milk processing
industry also incurs losses because of problems that result from
antibiotic in milk, and the reduced chemical and bacterial quality
of mastitic milk.
Mastitis micro organisms, usually bacteria, originate in various
sites on the cow. They multiply in various ways and are spread from
cow to cow.
Most common types of mastitis bacteria originate in the udders of
infected cows and in sores on the teats, which multiply and are
spread during milking, from infected quarters and teat lesions.
Other serious forms of mastitis are caused by bacteria which come
from other sites on the cow (e.g. in dung). These bacteria multiply
in bedding materials and spread of the bacteria from dung etc that
multiplies in bedding materials. Mastitis inflammation can be detected
by simple tests on cow’s milk (eg CMT test) but the causative
bacteria can be detected only by laboratory tests.
Several microbial diseases of the udder that are collectively known
as mastitis are distinctly different. The pathogens can arise from
different primary sites, which multiply in different environments
and therefore, the timing of the cow’s exposure to the bacteria
will vary. Subsequently the acuteness and persistency of the infections
differ and also the probability of cure when therapy is given [6].
The commonest forms of mastitis in most countries are caused by
S. aureus and Str. agalactiae. The primary sites of these are infected
quarters and spread mainly at milking, either during udder preparation
or on hands and milking machines. These pathogens can colonise and
multiply in teat sores and in teat ducts and this greatly increases
the degree of exposure of the teats to bacteria. They usually cause
chronic infections which persist in the sub clinical form and occasionally
become clinical when abnormal milk can be detected. Systemic infection
with loss of appetite and raised body temperature is infrequent.
When suitable antibiotic preparations are infused into the udder,
the clinical mastitis nearly always subsides and most Str. agalactiae
infections are cured but with staphylococcal infections the cure
rate is poor and mostly persists.
Infections caused by Str. umbers and E. coli are often called environmental.
The main primary sites of the pathogens are bovine, but not from
within the udder. These do not normally colonise teat skin and the
multiplication occurs in organic bedding materials (e.g. straws
and sawdust). These types of infection are most common in housed
cattle in early lactation, and whilst they can cause persisting
sub-clinical mastitis the more typical from is clinical mastitis.
Soon after the onset of the infection, and with coli form mastitis
the endotoxaemia causes raised body temperature and marked reductions
in milk production. Str. uberis infections usually respond to therapy,
but with E. coli infections it is important to give supportive treatment
to overcome the endotoxaemia and if this is successful, spontaneous
recovery usually follows [6].
Str. dysgalactiae is similar to Str. agalactiae and S. aureus in
that it can readily colonise and multiply in teat lesions but the
main primary site is not the milk of infected quarters, but other
bovine sites. The course of the infection is not dissimilar to Str.
agalactiae and infections respond readily to antibiotic therapy.
Many other micro organisms can cause mastitis. These less common
forms are not usually important but pseudomonads and Mycoplasma
bovis do cause serious problems in a few herds [6].
Although the pathology of the various types of infection show distinct
differences, the causes of infection can be diagnosed with certainty,
only by bacteriological tests made on aseptically-taken quarter
milk samples [6].
An udder quarter becomes infected when the teats are exposed to
pathogens, which then penetrate the teat duct.
6. SYSTEMS OF MILKING
Hand milking is a labour intensive system in which capital investment,
running costs, labour productivity and milking performance are minimal.
Clean milking clothes, buckets, udders and hands are essential for
good hygienic milk quality.
Cool the milk by immersing the cans of milk in clean, running water
or by inserting an in-can turbine cooler. Alternatively, use a corrugated
surface cooler connected to the water supply.
Clean the milking bucket and cooler by rinsing in clean water, scrubbing
in hot (45 °C) detergent/ disinfectant solution and finally
rinsing in chlorinated (50 ppm) water. Alternatively, after scrubbing
in hot detergent solution, disinfect by immersing in hot (75 °C)
water for at least 3 minutes. Afterwards treat ancillary equipment
similarly and allow all equipment to drain until dry, in a clean
place.
Statistics from all major milk producing countries indicate an annual
decline in the number and size of hand milked herds. Labour productivity
in these herds is low with very few cows per person involved. Duration
of milking each cow and the whole herd is protracted because each
person milks cows one at a time with a relatively slow milk extraction
rate, compared with machine milking. These are factors which contribute
to lower average lactation milk yields in hand milked herds. Nevertheless,
for small herds, hand milking will usually be the method chosen
because where there is sufficient labour available, it can provide
a satisfactory way of milk removal with minimal capital investment,
equipment maintenance and cleaning.
During milking, hygiene standards require clean milking clothes
and hooded milking buckets to prevent dust, dirt and udder hairs
falling into the milk. Udders and tails need regular clipping. Before
milking begins, the foremilk is drawn and examined, and visible
dirt removed from udders and teats by washing and drying with disposable
paper towels. Milk with clean, dry hands using the full hand in
preference to just finger and thumb, a practice which can lead to
injured udders and teats. It is best to milk rear quarters first,
as they contain the higher proportion of milk [6].
Milk cooling methods will depend mainly on the local water supply.
If the quality, quantity or temperature is unsuitable or unreliable,
then the milk should be taken, within 3 hours of production, to
a central depot for cooling. Where an unlimited free supply of clean,
cold (below 15 °C) water is available, the cans of milk can
be immersed in running water. Water usage can be reduced and cooling
rate increased by inserting a turbine in-can cooler into the cans
of milk. Alternatively, the milk may be tipped and allowed to flow
over a corrugated surface cooler connected to the water supply.
Cleaning the milking bucket and cooler is best done by an initial
rinse in clean water immediately after milking, followed by scrubbing
in a hot (45 °C or above) detergent/disinfectant solution before
finally rinsing in chlorinated water (50 ppm). Alternatively, after
scrubbing the equipment in hot detergent solution, disinfect by
immersing in hot (above 75 °C) water for at least 3 minutes.
The foremilk cup, stool and udder washing equipment should be treated
similarly afterwards. All equipment must be drained dry during the
interval between milking [6].
7. CONCLUSION
The data outlined and the statements made are intended only as a
source of information for Food Science and Technology students and
private industrial entrepreneurships.
Milk is used as a therapeutic weapon to combat against acidic toxicity
(e.g. toxicity from bitter cassava or tapioca which contains cyanohydrins
components). Finally, milk is a good source of nutrients that has
a high biological nutritional value for children, old men and feeding
patients.
Concerning Milk hygiene in Rwanda, the final milk product reaches
the consumer in the most acceptable and nutritive condition.
We are maintaining this condition to avoid contamination and reduction
of nutritive value of milk. If milk hygiene is neglected, there
are spoilage poisoning and reduction of shelf life. This is to say
that milk is preserved at the highest possible quality in our country.
8. REFERENCES
1. Nzabuheraheza FD Lecture notes: Science and Technology Courses
I & II of 3rd year. Department of Food Science and Technology,
Kigali Institute of Science and Technology, 2003
2. TETRA-Pak Processing Systems. Dairy Processing Handbook. Lind,
Sweden, 1995.
3. Eckles CH, WB Coms and H Macy Milk and Milk Products, 4th Edition
USA. Reprinted by McGraw-Hill Publishing Company Limited, New Delhi,
India.
4. Varnam AH and JP Sutherland Milk and Milk Products, Technology,
Chemistry and Microbiology. In Chapman & Hall, 1994.
5. JKUAT. Department of Food Science and Technology. Laboratory
Manual in Food Science and Technology. Nairobi, Kenya, 2003.
6. Kerr TJ and BB Mettele Applications in General Microbiology:
A Laboratory Manual. Winston-Salem, Huner Textbooks, 2001.
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