Use of commercial somatic cell counters to quantify somatic cells in non-lactating bovine mammary gland secretions

Abstract

Measurement of the somatic cell count (SCC) in milk is commonly used to detect mastitis in lactating dairy cows. Many techniques and tools have been developed and adapted to quantify milk SCC, but few tools have been evaluated in their ability to enumerate somatic cells in non-lactating bovine mammary secretions. This limits the tools available for detecting mastitis in non-lactating animals. The objective of these studies was to evaluate methods of somatic cell quantification, originally developed for milk, in their ability to quantify the SCC in non-lactating bovine mammary secretions when compared to the gold standard microscopic quantification method. Two experiments were conducted. In a first experiment, 222 mammary secretions were collected and diluted 1:10 with PBS. Cells in these suspensions were quantified microscopically and with a DeLaval Cell Counter. Microscopic SCC (MSCC) ranged from 1.9 × 10⁶ to 259.5 × 10⁶ cells/mL while DeLaval Cell Counter SCC (DSCC) ranged from 1.8 × 10⁶ to 27.0 × 10⁶ cells/mL; a measurement of agreement between the 2 measures, based on the Lin's Concordance Correlation Coefficient (CCC) suggested moderate agreement between measures (CCC = 0.60). In a second experiment 72 mammary secretions were collected and diluted 1:50 in PBS. Somatic cells in these suspensions were quantified microscopically, with a DeLaval Cell Counter, and by a DHIA laboratory using a Fossomatic™ FC. MSCC ranged from 1.6 to 47.5 × 10⁶ cells/mL, DSCC ranged from 1.0 to 35.7 × 10⁶ cells/mL, and Fossomatic SCC (FMSCC) ranged from 1.6 to 46.7 × 10⁶ cells/mL. CCCs of 0.81 and 0.88 resulted when DSCC and FMSCC were paired with the MSCC, respectively. The results of this work indicate that a significantly greater concentration of somatic cells exist in non-lactating mammary secretions and dilution of these mammary secretions influences accuracy of SCC estimates. Future studies seeking to quantify somatic cells in mammary secretions from non-lactating cows should identify the most appropriate dilution factors specific to each method of measure, given that these two factors will influence the accuracy of SCC estimates. Development of a standardized approach for quantifying somatic cells in non-lactating dairy animals such as heifers and cows, via a rapid automated counter, can allow for the detection of mastitis in non-lactating dairy animals.

Keywords: Dry cow; Heifer; Mastitis; SCC.