SOMATIC CELL COUNT - AN EFFECTIVE TOOL IN CONTROLLING MASTITIS
An Effective Tool in Controlling Mastitis
J.K Reneau, R.D Appleman, G.R. Steuernagel, and J.W. Mudge
Mastitis is the most costly disease on the dairy farm today.
Nearly 70 percent of this loss is a result of reduced milk
production caused by subclinical mastitis.
Mastitis is largely a management disease. To be successful in
controlling it, you must be willing to admit that the cause of
mastitis probably is due to your own managerial shortcomings.
The Minnesota Dairy Herd Improvement-Somatic Cell Count
(DHI-SCC) program is a management tool designed for use as an
integral part of a mastitis control program. Successful use of this
tool depends on your knowledge and understanding of the SCC report.
Proper use of this report not only will create an awareness of the
level of mastitis in your herd, but also will give you some idea of
what the most likely causes of your mastitis problems are. The
Minnesota DHI-SCC program is a herd mastitis prevention program,
not an individual cow treatment program. The emphasis is on
prevention, not treatment.
Herds Not on the SCC Program
If you do not have your herd on the DHI-SCC program, you can
get an idea of your situation by comparing your bulk tank Wisconsin
Mastitis Test (WMT) score to the standards shown in table 1. Bulk
tank WMT scores less than 6 or bulk tank cell counts less than
200,000 indicate there is no serious mastitis problem. If your
scores are within these ranges, your challenge will be to maintain
a clean herd. For you, the SCC program will be a monitoring tool
that will enable you to respond to potential problems before they
become a major concern. Bulk tank WMT scores greater than 8 or bulk
tank cell counts greater than 300,000 indicate significant
subclinical mastitis. If your scores are within these ranges, the
$66 program will be an aid in improving mastitis control.
Table 1. Comparison of bulk tank WMT scores with somatic cell
counts.
Subclinical mastitis
WMT SCC assessment of herd
6 or Below 225,000 Excellent: Maintain control
below measures.
8-12 300,000-465,000 Fair: Check for chronic cows and
introduce control measures.
14-16 565,000-675,000 Unsatisfactory: Subclinical
mastitis may be widespread in
your herd.
18-20 790,000-920,000 Poor: High level of infection present
in herd. Large dollar loss due
to mastitis.
22 or 1 million or Very poor: Immediate action called
above above for. Obtain individual cow
cow results. Cull or dry off
problem cows. DO NOT WAIT.
DO IT TODAY.
Interpretation of Individual Cell Counts
Before we discuss the interpretation of individual somatic
cell counts, let us review some basics. The term somatic cell is a
general term referring to the white blood cell. White blood cells
are extremely important in combating mastitis. If the udder becomes
infected or injured, large numbers of white blood cells migrate to
the mammary gland to destroy and remove either the bacteria or the
toxin they produce. Therefore, high somatic cell counts in the milk
are a strong indication of the presence of an infection.
Although the question of what represents a "normal" cell count
remains unanswered, there clearly is a linear relationship between
cell count and milk yield figure 1;(small version, large version).
FIGURE 1&2: CELL COUNT vs. PRODUCTION CHART
Linear Somatic Cell Count
The linear somatic cell count provides a more meaningful method of
evaluating mastitis in your herd. Linear somatic cell counts (SCC)
help you:
(1) measure effects of subclinical mastitis on your herd;
(2) identify cows affected by subclinical mastitis;
(3) measure reduction in subclinical mastitis as
improvements in management are made; and
(4) identify temporary or long-term problems that
might otherwise be undetected.
SCC Scores: Somatic cell count scores have been converted to
a "linear score" from 0 to 9. Each increase of 1 in score is
associated with a doubling of cell counts (see table 2).
The linear score has a straightforward relationship to loss of
milk yield (table 3). When you analyze your entire herd, it
emphasizes the economic losses occurring in your herd because of
subclinical mastitis.
The infiltration of white blood cells through the milk
secretion tissue, whether caused by infection or other tissue
irritation, results in lowered milk yield by that mammary tissue.
Each time the cell count doubles, the expected decrease in milk
production for older cows is approximately 1.3 pounds per day or
400 pounds per lactation. Corresponding figures for first lactation
cows are .6 pounds per day or 200 pounds per lactation. Producers
should, therefore, attempt to lower individual cow and herd cell
counts as much as is practical to take advantage of more efficient
production. Current evidence suggests that an average herd SCC of
150,000 or less is a reasonable and desirable goal.
Approximately 95 percent of cows with counts of less than
100,000 (linear score of 2 or less) would be considered free of
mastitis. Any cow with a single cell count of 300,000 or more
(linear score of 5 or more) can be considered infected. Cows with
a linear score of 3 or 4 should be considered "suspect." According
to research available, about 25 percent of these cows have
mastitis. As cell counts increase, production losses are generally
more severe (table 3).
Heifers generally have lower counts than older cows. A
reasonable explanation would be that since older cows have been in
the herd longer and have been milked more times, they are more
likely to have been subjected to management-induced mastitis. An
ideal goal would be that 90 percent or more of the cows in a herd
have counts less than 250,000 cells. A reasonable goal would be to
have 10 percent or less of the cows positively infected with
subclinical mastitis.
Table 2. Relationship of Linear SCC Scores to Regular Somatic
Cell Counts and California Mastitis Test.
Somatic Cell Count California
Linear Mid- Mastitis
SCC Point Range Test
0 12,500 0 to 17,000
1 25,000 18,000 to 34,000
2 50,000 35,000 to 70,000 Negative
3 100,000 71,000 to 140,000
4 200,000 141,000 to 282,000 Trace
5 400,000 283,000 to 565,000 1
6 800,000 566,000 to 1,130,000
7 1,600,000 1,131,000 to 2,262,000 2
8 3,200,000 2,263,000 to 4,525,000
9 6,400,000 4,525,000 and up 3
Table 3. Linear SCC Scores and Relationship to Daily and Lactation
Milk Yield Losses.
Daily Yield Lost Lactation Yield Lost
Linear First Older First Older
SCC Lactation Cows Lactation Cows
(....lbs./day....) (....lbs./lactation....)
0-2 0 O 0 0
3 0.6 1.3 200 400
4 1.3 2.6 400 800
5 2.0 3.9 600 1200
6 2.6 5.2 800 1600
7 3.3 6.6 1000 2000
8 3.9 7.9 1200 2400
9 4.6 9.2 .... ....
Interpreting Herd Summaries
The Minnesota DHI-SCC report has several herd summaries,
namely: Current SCC Summary figure 2;(small version, large version) Herd
Average SCC figure 3;(small version, large version) SCC Trends
(figure 4;small version, large version), and yearly SCC Summary
(figure 6; small version, large version).
Current SCC Summary figure 2;(small version, large version) evaluates
first lactation cows separately from older (other) cows. Since older cows
have been in the herd longer and have been milked more times, they are
more likely to have been subjected to management-induced mastitis.
When appropriate mastitis control procedures are used, 90
percent or more of the first lactation cows should be in columns
0,1, 2 or 3, with most of the remaining cows in column 4.
Any time several cows in either age bracket are in columns 5,
6, 7, 8 and 9, it suggests a need for you to review your mastitis
control program. Special attention should be given when there is a
marked shift, with more animals in a higher numbered column from
one sample day to another.
In figure 3;(small version, large version), Herd Avg SCC, the
number in the "Cells" section represents the weighted herd average somatic
cell count. It is calculated by multiplying each cow's sample day milk
yield times the number of somatic cells in her milk, summing over the
entire herd, dividing by total milk yield. Variation between Herd Avg SCC
and bulk tank count results can be expected. This variability is due to:
(a) variability in sensitivities of the different test methods used, (b)
sample day differences, and (c) some milk from specific cows being
withheld from the bulk tank.
FIGURE 3,4 & 6: SAMPLE HERD CHARTS
Estimated Daily Milk Yield Lost in W figure 3;(small version,
large version) (a computer printed statement on the line just below
the "herd average SCC") represents the estimated total herd loss in daily
production. It is calculated from each cow's current sample day linear SCC
score and the data presented in table 3. If this loss (i.e., 54 Ibs.) is
representative of each month, the milk is priced at an average value
(i.e., $12 per cwt.), the estimated annual loss in milk production on this
farm is $2,365 (54 lbs X $0.12 X 365 days).
SCC Trends
The trend summary categorizes the infection status of heifers
and older cows, comparing the percentage of infected heifers and
older cows from a current sample with samples from last month and
a year ago. This herd summary is useful for monitoring progress in
mastitis control over both the short and long term.
The heifers in the trend summary shown in figure 4;(small version,
large version) have remained clear of mastitis, indicating that
control procedures preventing cow-to-cow spread of mastitis are working
well. Progress also may have been made by successful dry cow therapy or
the culling of chronically infected old cows.
Drastic increases in the percentage of infected cows from one
month to the next (see figure 5; small version, large version) should
raise questions and initiate an investigation into what is happening:
1. Is there an equipment problem such as a loose belt on the
vacuum pump, a stuck vacuum regulator, a plugged vacuum line,
or any other equipment defect that might have a detrimental
effect on the milking characteristics of a machine?
2. Is a different person doing the milking?
3. Has there been a sudden and severe change in the weather, with
lots becoming muddy and cows becoming wet and dirty and
developing frozen teats or other teat problems?
4. Has there been a sudden onset of a disease process such as
pseudo cowpox or ulcerative mammillitis that might be causing
teat end damage?
FIGURE 5 & 7: SAMPLE HERD CHARTS
Yearly SCC Summary
The yearly summary considers the percentage of infected cows
or heifers relative to their stage of lactation. Determination of
when the most infections occur during the Iactation and in which
group (heifers or cows) they are occurring most often will enable
you to identify which management factors are the most likely cause
of the herd mastitis problem.
Mastitis control in the herd described in figure 6;(small version,
large version) is good. Heifers are freshening free from mastitis and
are remaining free of it throughout the Iactation. There are a few older
chronic cows in the herd that probably are being milked last. The
management techniques being used to control the spread of mastitis in this
herd probably include good milking equipment, recommended milking
procedures, general sanitation, effective feat dipping, and dry cow
therapy.
The herd described in (figure 7; small version, large version) is
experiencing a high incidence of mastitis in heifers soon after calving.
Some possible reasons would include unsanitary heifer maternity
facilities, udder edema, and calf sucking problems. In general, the level
of mastitis in this herd, except for heifers fresh less than 30 days, is
relatively good.
In such a case, searching for deficiencies in milking
equipment, milking procedures, feat dipping, or dry cow therapy
probably would be unproductive. Emphasizing heifer management
should solve the problem.
The herd described in figure 8;(small version, large version)
demonstrates the typical pattern that develops when there are poor milking
practices, marginal milking equipment, or the failure to feat dip or use
dry cow therapy consistently. Any one of these circumstances or any
combination of them can result in this type of pattern.
FIGURE 8 & 9: SAMPLE HERD CHARTS
Note that the heifers in this herd begin their Iactation, as
expected, with no infection. As the lactation progresses, however,
seemingly small deficiencies (failure to use separate towels to
wash and dry, failure to teat dip consistently, allowing too many
air slips, etc.) have the cumulative result of increasing the level
of mastitis. By the end of the Iactation, 60 percent of the heifers
in this herd are infected. The owner of a herd with such a pattern
needs to analyze milking equipment performance, milking procedures,
feat dipping, sanitation, and dry cow therapy.
Herds with mastitis problems due to multiple management or
equipment deficiencies throughout the dry period and Iactation may
not show any of these typical patterns. In such cases, all aspects
of mastitis control need serious consideration.
The yearly average percent SCC positive number, a computer
printed statement in figure 6;(small version, large version), indicates the
accumulated percent of all sample day tests conducted during the past year
that had a linear score of 5 or higher. It reflects the average situation
for your herd during the past 12 months.
Problem Cow List
The upper right of the herd summary (figure 10;large version) lists cows that have contributed a
significant portion of the bulk tank somatic cells. The cow's name or
number is at the left and the percentage of somatic cells in the bulk tank
coming from the milk of that cow is at the right.
The two cows listed in figure 9;(small version, large version) account
for 40 percent of the SCC for a herd. Kelly is contributing more than a
fourth of all cells, and Sally is contributing another 14 percent. Keeping
Kelly's milk out of the tank would lower the herd average SCC
significantly. If, for example, this herd had a herd average SCC of
365,000, removing Kelly's milk would lower it to 279,000.
If you are in the unfortunate situation of having a herd SCC
that approaches 1.5 million, withholding the milk from a couple of
cows often will reduce the bulk tank count and help ensure your
ability to remain on the market.
Individual Cow Data
Individual cows are identified by name or number in the sixth
column from the left on the SCC Summary (figure 10;large version). The column at the left is each cow's "computer
control number." Age of cow (Iactation number), stage of Iactation (days
in milk), and current month sample data (milk weight and linear SCC score)
are listed in the next three columns. Any cow with a linear score of 4
should be suspected of being infected. Cows with a linear SCC score of $
or more are considered to be infected (positive).
A "C" in the SCC Code column means this cow had a high somatic
cell count for two or more consecutive months since calving. A "P"
indicates the cow had a high SCC score during the previous
lactation. An "N" means this cow has a new infection or has been
reinfected after having had a linear score of 4 or less for two or
more months.
The number of new infections is listed after the last line of
cow data. Knowing the rate of new infections each month is helpful
in determining whether your mastitis control program is working. If
you have just begun some new mastitis control procedures, a
decrease in new infections may indicate that they are having an
effect. Any significant rise in the new infection rate may indicate
a breakdown in mastitis control procedures or may indicate
improperly functioning milking equipment.
Individual cow cell count data are useful in identifying
problem cows and as an aid in making culling decisions. When
possible, changing milking order so that high cell count cows are
milked last is a good means of reducing the spread of contagious
mastitis.
Monitoring the SCCs of individual cows at the end of Iactation
may aid in anticipating potential flareups during the early dry off
period. Certainly the cow with a consistently high SCC late in
lactation needs close observation during this critical period.
Discuss appropriate drying off procedures and dry cow treatment
with your veterinarian.
What About Treatment?
Obviously, all cases of clinical mastitis should be treated
whenever they occur. Generally, however, it is unwise to treat
subclinical mastitis (SCC linear score of 5 or more) during
lactation. Treatment of most subclinical infections during
lactation cannot be economically justified; the cost of treating
cows and discarding the milk far outweighs the benefits. Using
good milking procedures as well as teat dipping and dry cow
treatment are the most sensible ways of attacking this problem.
There is one exception to this general rule. If the subclinical
mastitis is caused by the organism Streptococcus agalactiae, there
is good chance that treatment during lactation will be effective.
If you decide to treat a subclinical case of mastitis, the infected
quarter must be identified (California Mastitis Test) and cultured
to determine the causative agent as well as its drug sensitivity.
Using SCC for Control
Here is a suggested approach for establishing a control
program using the SCC program:
1. Determine the severity of your mastitis problem.
2. If your herd average SCC is greater than 250,000 or the average
yearly SCC percent positive or very strong is greater than 15
percent, review your mastitis control procedures and your
milking equipment. Determine the nature of the infection by
collecting aseptically and culturing a composite sample from
cows with persistently high SCCs. Another way to characterize
a herd mastitis problem is to collect aseptically and culture
five consecutive bulk tank samples on special culture media.
This procedure should be coordinated with your local veterinary
clinic and processed through a veterinary diagnostic lab.
3 Review the control procedures you use. Start those practices
you are not using.
4. Have the adequacy of your milking equipment operation checked
twice each year.
5. Follow proper milking procedures.
6. Improve stall and lot sanitation and other practices, such as
clipping the udder, that help keep the udder clean and dry.
7. Use effective teat dips and dry cow treatment routinely.
8. Treat all clinical cases and cull chronic nonresponding cows.
9. Minimize the spread of new infections by milking infected cows
last.
10. Monitor the response of your control program by reviewing your
SCC report monthly.
Evaluation of John Dairyman Herd
The John Dairyman herd (figure 10;large version) has a low herd average SCC (204,000). His estimated daily
milk yield lost is calculated to total only $2,365 for the year if milk is
valued at $12/cwt. (0.54 cwt X $12 x 365 days). One distressing concern
about this herd is the increase in current infection rate (26% vs. 14%
last month and 4% one year ago). Fifteen percent (4 cows) of his herd are
newly infected since last sample day. This is considerably higher than his
yearly average of 9 percent SCC positive.
By inspecting the data in the "Yearly SCC Summary" section,
you must conclude that Mr. Dairyman is experiencing a high
incidence of mastitis in his older cows soon after calving. All
four of his newly infected cows have been fresh for fewer than 90
days. This may be the result of not consistently "dry treating"
cows at the end of their previous Iactation. Also there is the
possibility that his "dry cows" were maintained in wet, dirty
(unsanitary) conditions and contracted subclinical mastitis in this
manner.
A sudden increase in infection rate is sometimes the result of
a recent milking system malfunction. When this occurs, both first
lactation and older cows are usually affected.
If Mr. Dairyman wishes to insure continuation of his low herd
average SCC in order to qualify for a "quality bonus" on milk sold,
he would be advised to keep the milk produced by "Pearl" out of the
bulk tank and feed it to his calves. By withholding that milk, his
herd average SCC would be expected to drop from 204,000 to 156,000
cells.
The authors are extension dairy specialists.
Issued in furtherance of cooperative extension work in agriculture
and home economics, acts of May 8 and June 30,1914, in cooperation
with the U.S. Department of Agriculture. Norman A. Brown, Director
of Agricultural Extension Service, University of Minnesota, St.
Paul, Minnesota 55108. The University of Minnesota, including the
Agricultural Extension Service, is committed to the policy that all
persons shall have equal access to its programs, facilities, and
employment without regard to race, creed, color, sex, national
origin, or handicap.
FIGURE 10: SAMPLE SCC SUMMARY
%f TITLE;SOMATIC CELL COUNT - AN EFFECTIVE TOOL IN CONTROLLING MASTITIS
%f COLLECTION;DAIRY HERD IMPROVEMENT
%f ORIGIN;UNIVERSITY OF MINNESOTA
%f DATE_INCLUDED;OCTOBER, 1993
%t SOMATIC CELL COUNT - AN EFFECTIVE TOOL IN CONTROLLING MASTITIS