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Commentary [Volume 5 No. 2 (2005)]

 MILK PRODUCTION AN HYGIENE IN RWANDA

By
NZABUHERAHEZA François Dominicus

MSc. /Engineer (Ao) in Science and Technology, Ph.D. Cand.
Lecturer at KIST-Faculty of Technology
P. O. Box 3900 Kigali- Rwanda.
E-mail: nzabufd@kist.ac.rw


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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