Bacterial transport within and among various teatcup and cluster assemblies during milking

For evaluation of bacterial transport, two experiments were conducted. In Experiment 1, two nonconventional cluster designs were compared with a conventional assembly. These two units were: 1) conventional unit without a claw and 2) linerless unit without a claw. In Experiment 2, two nonconventional teatcup designs were compared with a conventional teatcup, all attached to a conventional claw. These two were: 1) partial linear teatcup assembly and 2) conventional teatcup with restricted linear wall movement. The three teatcups in Experiment 2 differed only in the lower part of the liner barrel; mouthpiece and short milk tube were identical. A culture of Serratia marcescens bacteria was infused throughout milking into the short milk tube at the right front teatcup assembly. Swabs of liners and teats were used to culture for Serratia marcescens. For Experiment 1, the number of contaminated teats (and liners) was 32 of 144 and 88 of 144 for the conventional cluster, 20 of 144 and 37 of 144 for the clawless cluster, and 10 of 144 and 16 of 144 for the linerless cluster. For Experiment 2, the total number of bacterial transfers was 14 of 25 for the conventional teatcup, 7 of 25 for the restricted liner, and 3 of 25 for the partial liner. These occurrences of transfer correlate well with previously measured reverse pressure gradients across the short milk tube.