Effect of vacuum level on bovine teat-tissue and milking characteristics

The effects on teat-tissue characteristics and milking characteristics of regulator vacuum levels of 44, 47 and 50 kPa were investigated. Friesian-type dairy cows (n = 42) were randomised to three groups based on milk yield and milked in a 3 X 3 latin square design experiment. Cows were milked with a mid-level milkline (1.2 m above the cow standing), 4 X 0 pulsation and wide-bore tapered liners (31.6 to 21.0 mm) and 3-kg clusters. Cluster vacuum measurements were recorded using a milk How simulator. Milk yield (MY), milking time (MT) and peak flow rate (PFR) were recorded at each milking using electronic milk meters. Clusters were removed at a milk flow rate of 0.2 kg/min. Milk samples from AM milkings were analysed for gross composition. Ultrasonography was used to compare teat-tissue characteristics before and after milking for each regulator vacuum setting. Teat measurements recorded were teat canal length (TCL), teat diameter (TD), cistern diameter (CD), and teat wall thickness (TWT). A reduction in regulator vacuum level from 50 to 44 kPa did not affect MY but it increased MT (P < 0.001) by 56 s/cow. PFR increased linearly with increasing vacuum level (P < 0.001). There was no treatment difference in gross milk composition. TD increase was greater (P < 0.05) at a vacuum level of 50 kPa than at 44 kPa. A regulator vacuum level of 47 kPa led to minimum teat-tissue changes but cluster-on time was increased by 30 s/cow. It is concluded that reducing vacuum level will minimise teat tissue reaction but will increase cluster-on time and reduce PFR with no effect on MY or milk composition.