Interpretation of machine effects on the defence mechanisms of bovine teat tissue

The physical forces applied during mechanical milking may cause changes in teat tissue integrity and conformation, in teat-related blood circulation and in cell populations, resulting in an impairment of the teat tissue immune capacity. To assess these changes, teat immune status was examined in eight cows after application of three milking systems: a conventional system (CON); a positive-pressure milking system (POP) and a non-pulsation system (NOP). Teat secretion samples (the first 1.5 ml of each quarter) were analysed for cellular and humoural defence parameters. The quartile distributions for all parameters during the pre-treatment (CON) were used as reference values; logistic regression was used to calculate the odds ratio for low (< 25%) and high values (> 75%). There were significant differences between all milking systems in both the low- and high-level categories of most parameters. Overall, the mean values were not as good predictors of extreme changes in humoural and cellular markers (particularly below the 25th and above the 75th percentiles) as were the odds ratios calculated here, even for changes in clinical criteria (teat thickness and length).