Incomplete milking has no detectable effect on somatic cell count but increased cell count appears to increase strip yield

Milking regimes that can greatly shorten the milking duration of slow-milking cows to improve labour productivity can also result in less complete milking for some cows. There is also a common belief and limited experimental evidence that incomplete milking of subclinically infected cows can cause increased somatic cell count (SCC). To test for this possible detrimental effect of shorter milking regimes, ‘complete’ milking [to automatic cluster remover (ACR) setting of 300 mL/min] and ‘incomplete’ milking (to an ACR setting of 800 mL/min) were applied sequentially to 45 cows over 7 weeks. Incomplete milking resulted in an average of 0.3 L of extra milk being left in the udders, but there was no significant increase in quarter SCC in either infected or uninfected udder quarters. Change in SCC was not related to change in strip yield induced by incomplete milking treatment. In contrast, cow strip yield was positively related to SCC, or the number of infected quarters/cow, regardless of the applied ACR treatment. These apparently contradictory findings are reconciled by noting that infection causes both high strip yields (via uneven yielding quarters) and high SCC. It is concluded that, contrary to popular belief, high SCC, as an indicator of infection, causes high strip yield and that increasing strip yield does not increase cell count.