Udder
infection
The essential requirements
are to maintain udders free from infection (eg. mastitis); manage cows so that
their udders and teats are clean; milk them in such a way that minimises
bacterial contamination; store the milk in clean containers and, wherever
possible, at temperatures which discourage bacterial growth until collected.
Simple and low-cost husbandry practises enable milk to be produced with a
bacterial count of less than 50,000 per ml. The golden rule of clean milk
production is that 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 subclinical 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/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 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.
Foremilking 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 milk 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.
Cleaning milk production
equipment
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
milkings, so that high numbers (eg 106 per m2) can be present on visually clean
equipment. A proven cleaning and disinfectant routine is required so that with
the minimum of effort and expense, the equipment will have low bacterial counts
as well as being visually clean.
The essential requirements
are, to use milking equipment with smooth milk 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 (ie. 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 the removal of dirt. Detergent
effectiveness is usually increased with increasing water temperature, and by
using the correct concentration and time of application. Detergents contain
inorganic alkalis (eg. sodium carbonate and silicates and tri-sodium phosphate),
surface-active agents (or wetting agents), sequestering (water-softening) agents
(eg. 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, providing that correct temperatures
are maintained during the process of 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.
When hot water alone is used,
it is best to begin the routine with water at not less than
85°C 185°F, so that a
temperature of at least 77°C
170°F can be maintained for at least 2 minutes. Many
chemicals are suitable as disinfectants, some of them combined with detergents
(ie. detergent-sterilisers). Use only those which are approved, avoiding
particularly those which can taint milk (eg. phenolic disinfectants). Always
follow the manufacturers 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, providing adequate contact time is given with the
surfaces to be cleaned and disinfected.
Milk premises
The milking premises should
have a dairy or suitable place equipped with a piped hot and cold water supply,
a washtrough, 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 - 100°C
32-212°F), rubber gloves and goggles for use when handling
chemicals.
Daily routines
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. 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
preceeds 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 milkings. 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 number of joints, remaining wet
between milkings in ambient temperatures above 20°C
68°F, should receive a
disinfectant rinse (50 ppm available chlorine) before milking begins.
