Changes in electrical conductivity and somatic cell count between milk fractions from quarters subclinically infected with particular mastitis pathogens

Abstract

Cows with subclinical intramammary infections were identified by milk bacteriology. The mastitis pathogens included Staphylococcus aureus (n=9), Streptococcus uberis (n=10) and coagulase-negative staphylococci (n=10). Samples of first fore milk, main flow milk and strippings milk fractions were collected from each quarter and laboratory measurements were made of electrical conductivity, milk fat concentration and somatic cell count. Conductivity measurements were corrected for milk fat concentration and within-cow inter-quarter conductivity ratios calculated. Repeatability estimates of all measurements between days were calculated. In the case of infected quarters, all conductivity values decreased markedly (P<0·05) from first fore milk to main flow milk fractions. Conductivity differences between quarters of infected cows were substantially lower during the main milk flow phase. For quarters infected with Staph. aureus an increase in conductivity was observed (P<0·05) from main flow to strippings fractions. For uninfected quarters, conductivity declined as milk fat concentration increased with successive milk fractions. Variation, both within and between milk fractions, was greater for somatic cell count than for conductivity. Differences in conductivity between milk fractions from individual infected quarters were not accounted for by changes in fat concentration and may result from the mixing of milk from infected and uninfected regions of the gland. Localized infection may produce a decrease in conductivity between fore milk and mid-flow fractions while differential drainage from an infection site in the secretory tissue may additionally produce an increase in conductivity from mid-flow to strippings fractions. Such changes may thus provide information on the location and magnitude of an infection. The results clearly demonstrate the importance of the milk fraction when using conductivity as a diagnostic of intramammary infection, the highest diagnostic sensitivity being achieved by using first fore milk samples.

Distribution of leucocyte populations, and milk composition, in milk fractions of healthy quarters in dairy cows

“…The steady increase of fat through all fractions up to its maximum in the residual milk agrees with former investigations (Woolford et al 1998;Ontsouka et al 2003b). This is probably due to the lower relative density of fat as compared with the water in milk and that there are capillary and adhesive forces, which influence the fat delivery by positive and negative membrane potentials.…”

Analysing serial data for mastitis detection by means of local regression

“…The EC of milk depends on its point of measurement. The EC of foremilk, before alveolar milk ejection occurs, gives better information on the health status than other milk fraction (Woolford et al, 1998;Barth et al, 2000). Unfortunately, in the present study, the EC was averaged across the whole quarter main milk, and no measurement of foremilk was available.…”

Fractionized milk composition in dairy cows with subclinical mastitis

“…Therefore, the bloodborne electrolytes Na and Cl seem to pass into milk already at a low level of disturbance. They are more powerful parameters for mastitis detection than electrical conductivity, which is indirectly dependent on electrolyte concentration (Wheelock et al, 1966), but obviously also influenced by other milk constituents like fat (Fernando et al, 1981;Woolford et al, 1998). This is especially true towards the end of milking, when high electrolyte concentrations do not cause increased electrical conductivity at a simultaneously high fat content in these milk fractions.…”