Characterization of electrical conductivity in individual milk of cattle breeds reared in Alpine area

Mastitis is one of the most relevant sources of economic loss in dairy farms. Since direct information on udder health traits is generally difficult and expensive to collect, indirect indicators are often considered at individual level to check udder health status. Milk electrical conductivity (EC, mS) is positively correlated with mastitis, due to the increase of Na+ and Clconcentrations when an intramammary infection occurs. This trait has been recently introduced in the routine analyses of the South Tyrol Dairy Association laboratory (Bolzano, Italy) for individual milk samples. In order to conduct a preliminary characterization of milk EC in Bolzano province, 96,722 test-day records from 2,209 single-breed herds of Brown Swiss, Holstein Friesian, Simmental, Alpine Grey and Pinzgauer cows for the period from March to December 2017 were retrieved from the database of the South Tyrol Dairy Association. The analysis of variance included the fixed effects of stage of lactation (12 classes), parity (6 classes), breed and their interactions; random factors were animal and herd-test-date nested within breed. All fixed effects included in the model were significant in explaining EC variation, with least squares means for breed effect ranging from 5.43 ± 0.02 mS (Pinzgauer) to 5.58 ± 0.01 mS (Holstein Friesian). Contrast estimates between breeds were significant, except for the comparison between Brown Swiss and Alpine Grey. Breed-specific EC lactation curves exhibited similar shapes, even if with different intercept values. The trends of EC among parities were similar between the five breeds, with a progressive increase of EC in subsequent lactations. Pearson’s correlations computed for each subset of breed highlighted that EC correlated with SCS in all breeds, with values that ranged from 0.22 (Holstein Friesian) to 0.35 (Pinzgauer). Moreover, EC strongly negatively associated with lactose percentage, with an average value of -0.75. These findings will be useful to better address future investigations and to understand how to exploit this milk feature.