week ONE: A Tool Box for Assessing Cow, Udder and Teat Hygiene
Paper presented at the 2007 annual meeting of the NMC, by
Nigel B. Cook and Douglas J. Reinemann
University of Wisconsin-Madison
Infection of the mammary gland with environmental bacterial pathogens is the most significant udder health problem facing the dairy industry in North America. Forty years ago, Neave et al. (1966) stated that the rate of new intra-mammary infection is related to the number of bacteria that the teat end is exposed to, and several studies have made associations between clean housing, clean cows and lower bulk tank somatic cell counts (Bodoh et al., 1976; Barkema et al., 1998; Barkema et al., 1999). In addition, Bartlett et al. (1992) found that an index of environmental sanitation based on the amount of manure on the cow and in her environment was a predictor of the occurrence of coliform mastitis, and Ward et al. (2002) noted that in four study herds, the lowest incidence of mastitis occurred in the herd with the cleanest cows and the most satisfactory beds.
Despite the improvements made in so many other areas of the dairy industry, our ability to keep cows clean and to reduce the bacterial load at the teat end has improved little. Increases in herd size, poor stall design, infrequent alley scraping and manure removal, pressure for milkers to increase parlor throughput, and changes in the availability and use of different bedding materials have all worked against significant progress in this area. Moreover, our inability to accurately document the effects of these failures has allowed detrimental changes in management to be amplified.
The clinician presented with an environmental mastitis problem must have a tool box at his/her disposal that serves to communicate the problem of environmental contamination to the herd owner, so that interventions can be made and improvements documented. This paper serves to track environmental contamination from its sources (manure and bedding), through contamination of the teat end and failure to adequately clean the teat, to contamination of the milk and infection of the mammary gland.
The predominant sources of coliforms and environmental streptococci (S.uberis, S.dysgalactiae, Enerococcus spp.) are manure and bedding materials. The cleaner we can keep the cows and the lower the bacterial count of the bedding, the fewer problems we will see. The tools we have to assess the degree of contamination in the environment are hygiene scores of the cows, culture of the bedding and assessment of teat end contamination.
Tools to Assess Udder Contamination
Several different methods of hygiene scoring have been documented (Cook, 2002; Schreiner and
Ruegg, 2003; Reneau et al., 2005) and some have been used to prove that poor hygiene results in
udder health problems. Schreiner and Ruegg (2003) used the udder hygiene scoring system in
Figure 1 to document the degree of contamination of 1250 cows in 8 herds. Udder hygiene
scores averaged 22% score 3 and 4 and a significant association between poor udder hygiene and
increasing individual cow linear score and the prevalence of intramammary infection with an
environmental pathogen was reported. In fact, cows with udder scores of 3 and 4 were 1.5 times
more likely to be infected with a major pathogen than cows with scores of 1 or 2. The study
reported only a weak association between leg hygiene score and the prevalence of pathogen
isolation from the udder.
Figure 1. Udder hygiene scoring chart available from UW Extension.
Reneau et al. (2005) used the more complex scoring system in Figure 2 to document hygiene in
1,093 cows in 8 herds and showed a significant association between udder and lower leg hygiene
and individual cow linear score measured within 2 days of recording.
Figure 2. Hygiene scoring system used by Reneau et al., (2005) which serves to document the
degree of manure contamination in 5 different areas using a 5 point scale.
While these hygiene scoring tools have been useful for research and documentation of the degree
of udder contamination, they do not communicate the reasons for manure contamination of the
udder very well. There are four basic manure transfer mechanisms to the udder, and the relative
importance of each differs with the type of housing under consideration:
1. Direct Transfer. Cows may lie down in a manure contaminated stall or bedded area (or
sometimes in a traffic alley!) and transfer bacteria directly to the udder.
2. Leg Transfer. Cows may walk through manure, coating their feet and legs, which
transfers bacteria to the teat ends when the cow lies down and the udder comes to rest on
one of the hind feet (Abe, 1999).
3. Splash Transfer. Cows walking though deep liquid slurry will splash manure up toward
4. Tail Transfer. In some situations, the tail may become heavily contaminated with
manure and transfer bacteria to the rear udder and flank areas (Abe, 1999).
The pattern of manure contamination and the mechanism of transfer therefore becomes a very
important concept to communicate to the herd owner. With this knowledge, the most appropriate
intervention can be recommended and for that reason, the author uses a simplified multi-zone
hygiene scoring system (Figure 3), scoring the udder, lower legs and upper leg and flank zones
of cows on a 1-4 scale. For reasons of communication, the proportion of scores that are 3 and 4
are presented, rather than a mean hygiene score. During investigations, we typically score 20%
of the cows in each pen, or all of the cows in small herds.
Figure 3. A hygiene scoring card which documents the degree of manure contamination on a 1-4
scale for each of three zones, the udder, the lower leg and the upper leg and flank.
The hygiene scoring data from 58 farms collected by the SVM food animal production medicine
group suggests that on average, 19% of udders are score 3 and 4 and have an elevated risk of
infection. While tie stall cows generally have cleaner lower limbs and less leg transfer, direct
transfer is the predominant means of manure contamination of the udder – from manure
deposited on the stall surface. Upper leg and flank scores are usually much poorer than in free
stalls, reflecting the risk associated with spending around 22 hours per day in a tie stall.
In contrast, the lower legs of free stall cows are far more contaminated than tie stall cows and leg
transfer is a significant risk for udder contamination. Splash transfer in poorly draining alleys is
Table 1. Median and upper quartile proportion of hygiene scores 3 and 4 for each zone for
cows in 58 Wisconsin dairy herds by housing type (46 Free stall and 12 Tie stall).
There are many factors involved in creating the pattern of manure contamination observed in
cows on our dairy farms and these have been discussed in more detail elsewhere (Cook, 2004). A
very common finding however, is for cows in sand bedded herds to be cleaner than in mattress
herds bedded with sawdust (Table 3). This finding may be due to the cleaning effect of sand,
differences in cow behavior in barns with the two different types of bedding surface, and less
slipping and splash transfer in sand bedded herds.
Table 3. Least squares mean (SE) hygiene scores (Proportion scoring 3 and 4 for each zone)
obtained independently by two observers from a minimum of 20 cows in the high group
pen on 12 free stall herds (6 sand and 6 mattress) compared using 1-way ANOVA.
In recent years, with the commercial availability of a service to perform bedding cultures at the
Udder Health Laboratory at the University of Minnesota, it has become routine to determine
bacterial contamination of the bedding. We typically compare fresh bedding material with that
sampled from beds after several days of use. We use a gallon ziplock bag to gather handfuls of
bedding from the rear of 10-15 stalls in each pen. The sample is mixed and sub-sampled into a
quart ziplock and frozen until the sample is sent on ice to the laboratory for analysis.
Recommendations from the literature suggest that the total count of bacteria in used bedding
must not exceed 1 million CFU/ml. However, while this threshold appears to be valid for organic
bedding materials, considerable experience from clinical investigations suggests that this
recommendation is flawed in the case of sand bedding.
Table 4 shows the median and upper and lower quartile bedding counts for coliforms and
streptococci for 82 sand bedding samples collected from 23 farms. These counts would suggest
that coliform mastitis would not be a risk, but streptococcal infection would be a major problem.
In fact, in these 23 herds, the proportion of mastitis due to gram negative pathogens averaged
75%, and mastitis due to streptococci was rarely a major problem.
Table 4. Coliform and streptococci counts (CFU/ml) for 82 used sand bedding samples from 23
Thresholds used by the author differ from published data. We have found significant gram
negative mastitis problems (Klebsiella spp in particular) at a coliform threshold of 100,000/ml,
and this is typically used as our intervention level. Even lower counts have been used in very
cold weather during the winter. Streptococcal counts in sand can rarely be kept below 1 million
/ml, and high counts usually reflect the duration of sand retention in the beds – ie. we can keep
the count lower by increasing the turnover rate of the material.
We have successfully improved the rate of clinical mastitis and lowered herd BTSCC by
removing contaminated sand bedding and changing to coarser screened sand rather than fine
sand (Cook, 2006). The 1314 cow dairy shown in Figure 4 was suffering an extremely high gram
negative clinical case rate in the summer of 2002. Following sand removal and replacement, the
case rate was halved in 2 months and returned to target levels within 6 months.
Figure 4. Quarter cases of clinical mastitis by month before and after sand removal from the free
stalls in a 1314 cow dairy in November 2002.
More recently, a 1400 cow dairy was visited in February 2006 with contaminated compacted
sand stalls. The sand was removed and replaced with a coarse washed mason sand. Not only did
cow comfort improve, but clinical treatment rate and bulk tank SCC was halved within one
month (Figure 5). In these herds, we now keep the coliform counts in the bedding less than
10,000/ml and see many fewer gram negative clinical cases.
Figure 5. SCC response at a 1400 cow dairy where sand was removed from stalls in February
2006 and the fine sand replaced with coarse washed mason sand.
Correlations between bedding counts and teat end contamination have been made (Zdanowicz et
al., 2004) and confirm that higher correlations are generally made for organic bedding than for
sand. In particular, the correlation between streptococcal sand bedding counts and teat end
counts is low (r=0.28, P=0.06), compared with that for Klebsiella spp (r=0.40, P<0.05). More
research is needed to fully understand the transfer mechanisms of pathogen groups from the
bedding to the udder, but in the mean time, these anecdotal reports confirm that dramatic
improvements in udder health can be achieved by lowering the teat end challenge from
contaminated bedding, and bedding culture has a role to play in quantifying this challenge.
Tools to Assess Teat Contamination
Teat end sanitation is important in reducing the number of bacteria at the teat end before the
milking unit is attached, thus reducing transfer of organisms from cow to cow by the milking
machine. Proper teat end disinfection can reduce teat surface bacteria by 75% (Ruegg et al.,
2000; Galton et al., 1984; Galton et al., 1986). Pre-dipping with a sanitizer was associated with
reduced pathogen content in milk (Hassan et al., 1999) and has been shown to be effective in the
control of environmental pathogens (Pankey, et al, 1987; Ruegg and Dohoo, 1997). While
cleaning teats with water and wiping dry reduces the number of microorganisms on the teat skin,
the reduction is significantly higher when teats are disinfected (Brito et al., 2000). Contact time
of 20-30 seconds is needed for effective disinfection for most sanitizers.
If washing is required to remove excess manure, the following methods have been demonstrated
to significantly reduce pathogen numbers: 1) only teats should be washed, 2) minimal water
should be used, 3) teats should be thoroughly dried (Rasmussen, 2000). The most important
portion of the teat disinfection process is thorough drying of teat ends. Air-drying is not a
satisfactory substitute for manual drying with an individual cloth or paper towel. Water on teats
aids in transporting bacteria and concentrating them at the opening of the teat canal. Cloth towels
were more effective than paper at removing pathogens in a study by Rasmussen et al., (1991).
When cloth towels are used they should be disinfected by washing with bleach or very hot water
and drying at high temperature in an automatic dryer (Fox, 1997).
The tools we have available to determine the degree of teat end contamination are culture of the
bulk tank and string samples from sub-groups within the herd, and direct swabbing and culture of
the teat ends.
Culture of Bulk Milk and String Samples
Bulk tank cultures are routinely submitted from many farms in North America. While they are
predominantly used to monitor for the presence of „contagious‟ pathogens (Mycoplasma,
S.aureus and S.agalactiae), counts of coliforms and environmental streptococci (non-agalactiae
streps) are also made.
Unfortunately, high levels of environmental bacteria in the bulk tank are difficult to interpret and
frequently the wrong conclusions are made. In simple terms, coliforms and streptococci may
enter the bulk tank from three sources – udder infections from the cows, teat contamination from
manure and bedding, and from the milking machine itself if a biofilm exists. High coliform
counts do not automatically mean that the milkers are not cleaning teats adequately!
Often, culture of sub-populations within the herd, such as cows with the last 3 SCC tests
>200,000/ml, can enlighten the interpretation of bulk tank culture, as it is not uncommon to see
environmental pathogens from the bulk tank (such as Klebsiella spp and S.dysgalactiae)
represented in a high proportion of chronically infected cows which shed large numbers of
Sand bedded herds typically suffer very high levels of streptococci in the bulk tank. Bedding
counts can be extremely high and if sand particles are not removed from the teat end adequately,
then large numbers of streptococci can appear in the bulk milk. Often, adding an extra wipe to
the procedure in sand bedded herds can dramatically reduce the streptococci count in the bulk
Despite the difficulties in interpretation, samples of bulk tank milk or sub-samples of milk from
groups within the herd can be used to help monitor hygiene in the following ways:
1. A base line “low level‟ of coliforms and streptococci must first be identified for the herd
or group being milked to answer the question – “what is the lowest achievable level based
on milking procedures?‟
2. Deviations from the base-line can be tracked over time for milker shifts in order to
determine departures from the normal using string samples
3. If significant departures occur, the cow must be ruled out as a source using individual
cow culture, and the adequacy of teat preparation must be determined by visual
Provided that these guidelines are followed, herds may use culture of the bulk milk or of string
samples to determine the adequacy of teat cleaning by the milkers.
Visual Assessments of Contamination
Filter Socks can be visually assessed at the end of each milking or “string‟ as an estimate of the
relative contamination of teats at the time the milking units are attached. It is also possible to
culture these filters to determine the major types and relative magnitudes of bacteria present on
teats and in udders at milking time.
To check the effectiveness of teat sanitation and drying, teat end swabs can be taken. A clean
swab can be rubbed across the end of the teat prior to unit attachment. A swab from a properly
prepared teat will remain clean, while a dirty swab indicates that teat preparation methods should
be improved (Figure 6). This technique may be of use on a small number of individual cows, but
unlike hygiene scoring, which cannot be easily influenced on the day of capture, it is very easy
for milkers to modify their teat preparation procedure to improve teat cleanliness scores over the
duration of data capture. As such, benchmarks for the proportion of teats that are too dirty have
not been developed and the test remains something that can only be used to demonstrate
effective teat prep on an individual cow basis.
Figure 6. Teat Cleanliness Scorecard developed by WestfaliaSurge, using a 4-point scale to
assess the degree of manure and bedding contamination at the teat end after completion of the
preparation procedure, prior to unit attachment.
Quantitative Assessment of Teat End Contamination
Several attempts have been made to quantify bacteria numbers on teats before milking using
swabs or rinses combined with subsequent plate culture methods. More recently,
bioluminescence assessment methods have been described. The need to assess automated teat
cleaning in robotic milking systems has spurred activity in this area. Slagjuis et al, used both a
cobalt tracer (2004a) and poppy seeds (2004b) mixed with manure and manually applied to teats
before cleaning to assess efficacy of teat cleaning. Meline et at. (2004) used Clostridium
tyrobutyricum spores added to a manure slurry and applied to teats before cleaning to assess
Knappstein et al. (2004) reported on the use of both total bacteria counts and ATP measurements
of teat swabs for assessing teat cleaning efficacy. They recommended an ATP based method as a
pragmatic evaluation of teat cleanliness on farms with either automatic or conventional premilking
preparation. To date, these methods have not found wide application for routine field use
because of their cost, complexity, large cow-cow variability and/or considerable variability
introduced by small changes in sample technique. Efforts are underway to develop improved
methods that are easier to use in the field and yet provide useful information on the real bacterial
challenge at the teat end.
The dairy industry in North America continues to face the daunting task of reducing new intramammary infection rates from the environment. The changing face of the industry has not helped our chances of improving hygiene. However, armed with some of the tools described in this article, the investigator can determine the extent of manure contamination and the reasons for it, evaluate the bedding material as a risk for infection, determine the effectiveness of teat end preparation before milking, and monitor the sources of contamination of the bulk tank milk with environmental pathogens. With these quantitative tools, interventions can be targeted at the most appropriate areas on the farm and subsequent progress monitored.
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