Monitoring of goats' health status by on-line analysis of milk electrical conductivity = Monitoraggio dello stato di salute delle capre attraverso l'analisi on-line della conducibilità elettrica del latte

Introduction - Infections of mammary gland are the major cause of mastitis that can affect the quantity and quality of milk. Somatic cells count is a common method to detect them. However, laboratory support is required. For this reason, other parameters have been considered to monitor, online, the animals' health status, such as the electrical conductivity of milk (EC). In dairy cows, this parameter has reached useful results. In dairy goat researches, moderate performances have been reported. These studies mainly use univariate methods. They do not consider the intrinsic variation of animals and they use simple thresholds. More efficient univariate methods, to evaluate the EC of gland milk, similar to those already used in dairy cows, have not been reported yet. Aim - The aim of this study was to evaluate the detection characteristics of milk EC. Univariate method, in which relative trends were considered, was evaluated and compared with those reported in literature. Materials and methods - EC measurements were acquired daily, on-line, from each gland. A "moving average model" was used to predict EC values, starting from the ten previous milkings. Differences between the predicted and measured values were calculated. In case these values overcame a specific threshold, positive results were defined. Comparing the obtained results with the laboratory analysis, the accuracy of the method was figured out as specificity and sensitivity. Results and discussion - No cases of clinical mastitis were observed. However, a high prevalence of not healthy (NH) glands was found (59,6%). This result was mainly due to the most prevalent mastitis agent observed: the Coagulase-negative Staphylococcus (CNS - 89,7%). In small ruminants, this organism is frequently associated with subclinical mastitis, becoming a chronic infection. Somatic cells count showed to increase during lactation (from 5,24 to 5,46 log SCC/mL) and was higher in milk samples from NH glands (5,29 vs 5,41 log SCC/mL), showing trends as reported in other studies. The accuracy reached by the univariate method investigated was: a specificity of 65% and a sensitivity of 81%. These results were better than those reported in literature about univariate methods, confirming that the use of on-line daily measurements, and EC differences between predicted and observed values, can lead to more accurate on-line healthy detection systems. Furthermore, results allowed to define a performance reference useful to compare the improvement bring by other EC indexes, used in more complex and multivariate methods. However, results obtained showed to be generally less if compared with those reported for dairy cows. Conclusions - The univariate method analysed, based on gland milk EC, showed to be better than those previously published. These results confirm what supposed in recent published researches and what already done in monitoring systems applied to dairy cows. Furthermore, results obtained will be useful to evaluate new methods, more complex and based on multivariate approaches. These methods will be developed in order to reach, also for dairy goats, the same performances of dairy cows monitoring systems.