Somatic Cell Count Basics for Dairy Sheep

Introduction

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, 2000).

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.

Factors that affect SCC in sheep and management tips to minimize the effects
Table 1. Factors that affect SCC in sheep and management tips to minimize the effects
Factor
Effect on SCC
Management Tip
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.

Age

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

Infection Status

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.

Flock management

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 flock increases.

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 sheep flocks

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.

Breed

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


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: Jeromy Ten Hag - Milk Quality Assurance Program Lead/OMAFRA
Creation Date: 1 February 2002
Last Reviewed: 13 April 2010