Normal Milk Conductivity Variation Throughout the Lactation

Milk conductivity has been evaluated for mastitis detection in the past without a clear picture of how it works. The information shown in this descriptive study shows the normal variation that occurs throughout the lactation in dairy cows.

Data from different farms was used for this study. All farms had milk meters equipped with conductivity probes (Afimilk, Israel). Cows were automatically identified in the milking parlor, and their milk production and conductivity level (mmHO) were recorded at every milking throughout the entire lactation.

Figure 1 shows normal conductivity variation throughout the lactation in a 4,000 Jersey cow dairy divided by lactation number. Notice the sharp decrease of conductivity in the first week of lactation. This decrease corresponds with the clearing of colostrum from the udder. First lactation cows maintain steady conductivity throughout the entire lactation, while adult cows increase in conductivity toward the last third of the lactation. Average conductivity for all cows in the herd was 10.00±0.31 mmHO. Average conductivity differed by lactation (P< 0.001); 9.41±0.10 mmHO in 1st lactation, 9.93±0.26 mmHO in 2nd lactation and 10.23±0.42 mmHO in 3+ lactation cows.

Figure 2 shows normal conductivity variation throughout the lactation in a dairy with 60 Holstein and 60 Jersey cows. Both breeds show similar curve patterns, with no significant differences (P=0.637): Holstein cows at this farm had on average 9.96±0.32 mmHO and Jersey cows had 9.97±0.44 mmHO. These average values approached statistically significant difference from those of the large Jersey farm in Figure 1 (P=0.069).

Given the natural variation throughout the lactation, between lactation numbers, and potentially between farms, a single standard conductivity breakpoint to detect mastitis in all dairy farms cannot be considered. It would be similar to determining what milk production is ‘adequate/normal’ using a single number to be valid throughout the lactation of the cow. This number could be potentially too low for fresh cows and those in peak production, and possibly too high for cows at the end of lactation. Therefore, to use conductivity effectively for the detection of cows with mastitis, the deviation of conductivity from the normal pattern for that cow in that lactation should be used.