Development and test of a portable device to monitor the health status of Sarda breed sheep by the measurement of the milk electrical conductivity

The electrical conductivity (EC) of milk is a parameter which is often used for identifying sub-clinical
mastitis in dairy animals. It is widely used for cattle, and is measured either by means of probes
integrated into the milking machine or by means of portable devices. However this is not the case
for small ruminants, where the available devices are few. The aim of this study is to deepen the
knowledge of about the relationship between EC and certain constituents of Sarda sheep milk, and
thus to develop a portable device specifically designed for on-site measurement of conductivity
and to estimate the somatic cell count (SCC) of Sarda sheep milk. Therefore, the device allows a
rapid test for checking the acceptability of milk to monitor the effects of udder infection. The
receiver operating characteristic (ROC) method was used to evaluate how efficacious EC was in discriminating
between animals with a somatic cell level higher or lower of a threshold value previously
defined. The cut-off values, sensitivity, specificity and the area under the ROC curve for EC
were, respectively, 4.835 mS/cm, 73.08, 75.46 and 0.804, using a threshold of 700 000 cells/ml. Our
results gave a positive evaluation of the portable device that we had designed for estimating the
SCC in sheep milk. Only 8.8% of the samples were incorrectly identified as negative. A portable
device for EC measurement is a useful tool for monitoring the somatic cell level individually, and
allows early and efficacious action to contrast new intramammary infections.