Abstract
To probe the subclinical mastitis in a herd of cows in our institute, the conductivity of foremilk samples were measured fortnightly throughout a few lactational periods for 2.5 years. The difference in the conductivity at 25°C between samples obtained from different quarters of an udder was used as a parameter (quarter difference, Qd). Using 53 cows at 91 lactational periods, 362 quarters were examined and the following results were observed. 1) The percentages of quarters defined as normal, slightly abnormal or abnormal were 75, 10 and 15%, respectively. 2) The ratio of the normal quarter de-creased as the number of lactation progressed. 3) The mean Qd of the front quarters were significantly greater than those of the rear quarters. 4) The Qd values either fluctuated frequently or increased steadily in abnormal quarters. 5) In only less than one third of the quarters, the mean Qd of each quarter increased from one lactation to the next one. 6) The high Qd values were frequently observed in quarters which received a mastitis treatment previously.
