Somatic Cell Count Basics
for Dairy Sheep
Somatic cell count (SCC) is a measure of the
white blood cell count in milk. The SCC in milk of an individual
ewe indicates her udder health status, and bulk tank milk SCC can
indicate the general state of udder health in a sheep flock. Somatic
cells are always present in milk, but the SCC will rise when an
infectious agent enters the udder or when the udder has been injured.
A major consequence of rising SCC is a decrease in raw milk quality,
which has implications for milk processing.
There is no clearly defined SCC threshold that represents
a healthy udder in dairy ewes. Research studies have found SCC levels
for a healthy udder could range up to 1,600,000 cells/ml. More recently,
researchers have indicated that the upper threshold for SCC in a
healthy ewe's udder should be 250,000 cells/ml (Pengov, 2001, Menzies,
There are negative economic consequences for the producer
if somatic cell counts are elevated in the sheep flock. A high SCC
is a strong signal of an udder infection, referred to as mastitis.
Common clinical signs of mastitis are a swollen udder half, abnormal
color of milk, or clots present in the milk. There are significant
costs incurred as a result of mastitis in dairy ewes. Costs include
the antibiotic treatment used to cure the infection, the loss of
milk withheld due to the antibiotic residues, the producer's time
to treat the animal, and a decrease in milk production for the remainder
of the lactation. High SCC has also been suggested as the main reason
for culling dairy sheep.
When a bulk tank SCC reaches levels above the upper
threshold for good udder health (250,000 cells/ml), producers should
begin to investigate possible udder health problems. Ewes may not
be exhibiting clinical signs of mastitis, but more than likely will
have sub-clinical mastitis infections. Using individual animal SCC
or the on-farm rapid test, California Mastitis Test (CMT), can help
in identifying ewes with sub-clinical mastitis. The presence of
sub-clinical mastitis may require a change in flock management practices
to minimize the risk factors that contribute to high SCC.
High SCC also has a negative effect on milk processing
through decreased yields and off-flavor development in finished
products. A recent study found that sheep milk with a SCC >1,000,000
decreased the cheese yield and increased the development of rancid
flavors in the cheese (Jaeggi, 2001). More research is needed to
define the acceptable sheep milk SCC for optimal cheese processing
in sheep milk.
Table 1. Factors that affect SCC in sheep and
management tips to minimize the effects
Factors that affect SCC in sheep and management tips to minimize
Effect on SCC
Stage of lactation
SCC can vary irregularly in sheep milk independent of presence
of udder infection, but normally SCC is higher in early
and late lactation.
Milking sheep in various stages of lactation all year round
could balance out the effects that stage of lactation normally
has on bulk tank SCC.
Milking sheep year round is normally not an option, so
focusing attention on managing the other factors that may
contribute to elevated SCC is important.
Generally younger ewes have lower SCC than older ewes
Adding young ewes in to the milking string will alleviate
the effects older ewes may have on SCC
Sub clinical and clinical udder infection can increase
SCC in milk
Identifying subclincal mastitis can be done by measuring
SCC for individual ewes or by performing an on-farm California
Mastitis Test (CMT).
Treat clinical cases with intramammary antibiotic therapy
to cure infections.
Treatment decreases the risk of the ewe becoming a chronic
high SCC animal. Consult with your veterinarian for an appropriate
therapy to be used. Be sure to follow the milk withdrawal
time prescribed by your veterinarian to prevent antibiotic
residues from contaminating the milk.
Collect a milk sample of the infected udder half prior
to treatment and send to a laboratory for bacteriological
testing immediately after collection. Your veterinarian
should be able to help in coordinating the sample submission
to the laboratory and will be able to interpret the test
results from the lab. A bacteria profile of the flock can
be a very good management tool.
Poor flock hygiene increases the risk of bacteria entering
the ewe's udder, hence increasing the risk of higher SCC
in the milk. SCC increases as housing density of the sheep
Dirty teats and udders increase the chance of bacteria
entering the teat canal. This increases the risk of a ewe
ending up with a subclinical or clinical udder infection,
which will increase the SCC.
Maintain dry and clean housing facilities to minimize bacteria
load that the udder and teats are exposed to. Make sure
pens are well bedded
Milking clean and dry teats is very important to reduce
SCC and udder infection. Apply a teat disinfectant that
covers the entire teat and dry wipe with a single use towel
prior to milking.
Apply a teat disinfectant immediately after the milking
unit is removed from the udder.
Little research has been done on teat dip use in dairy
If there is high incidence of subclinical mastitis, dry
ewe therapy may be an option to cure existing udder infections
and prevent new ones during the dry period. Consult with
a veterinarian for an appropriate therapy to be used
Vitamin E and selenium supplementation during the dry period
has been shown to decrease SCC in the following lactation.
Consult your veterinarian before administering treatment.
Milking equipment maintenance
Improper milking machine function can result in uneven
milk out, liner slips and damaged teat ends. These factors
can all have a negative impact on udder health.
Have your milking equipment dealer perform a thorough milking
machine performance analysis at least once a year to ensure
the proper function of the machine.
Timing and condition of Milk sample
SCC measures are routinely done on frozen ewe's milk, however
the most accurate measure is made on a fresh milk sample.
SCC is higher for ewe milk from the morning milking compared
to evening milking.
If possible submit fresh milk samples for somatic cell
count testing to get more accurate results.
The range in SCC that represent healthy or infected udders
may be different among breeds.
Be aware of the breeds that are susceptible to higher cell
counts, so the other factors that may cause high SCC can
be managed closely