Effect of duration of teat cup liner closure per pulsation cycle on bovine mastitis.

Measurements of teat end expansion and contraction times from step changes in pressure suggest that teat ends require a minimal duration of liner closure for response. Effect of duration of liner closure per pulsation cycle on susceptibility of the udder to infection was tested. Four durations of liner closure (liner more than half closed) were applied: zero, .17, .34, and .51 s per pulsation cycle. For the latter three treatments, duration of the liner more than half open was .66 s per pulsation cycle, resulting in pulsation rates of 72.3, 60.0, and 51.3 pulsations per min. Four groups, each of 10 British Friesian cows, were in a 4-wk experiment. High bacterial exposure of all teats was ensured by dipping them before and after each milking in a suspension of Streptococcus agalactiae and Streptococcus dysgalactiae. Numbers of quarters becoming infected per treatment group were 20, 11, 4, and 5. This result represents both a significant inverse linear and quadratic relationship between proportion of quarters becoming infected and duration of liner closure. We conclude that a sufficient duration of liner closure, i.e., one-third of a second or more, per pulsation cycle contributes to reducing risk of new mammary gland infections.