DairyNZ senior scientist Dr Jane Lacy-Hulbert said while people need to expect some consequences in the first few milkings as things get back to normal, cows cope remarkably well with short-term milking disruptions. When milking activity stops the udder naturally begins the process of involution, where the various cells in the udder start to prepare to stop producing milk.
Fear not – this sequential process takes up to 30 days, starting with milk production declining, then milk composition changing, and finally the udder preparing itself for the next lactation.
Research from 2005-06, spearheaded by scientists Dr Dawn Dalley and Dr Steve Davis, showed cows in mid-lactation can go up to seven days without being milked and can return to full or near-full milk production with careful handling.
The trial, based at the Westpac Taranaki Agricultural Research Station (WTARS), tested the impacts of missing milkings for two, four and seven consecutive days.
Milk yield, somatic cell count (SCC) and the incidence of mastitis were recorded once the normal milking routine resumed, with 12 cows in each of the three treatment groups.
The trial found the two- and four-day treatments had significantly more milk at their first post-disruption milking than the seven-day treatment group.
For the 24-hour period immediately after resumption of the normal twice-a-day (TAD) milking routine, the cows over all three of the treatment groups produced less milk than before the missed milkings.
Within four days, milk yields for the two- and four-day treatment groups were similar to pre-disruption levels. The seven-day treatment group took six days to recover to close to those levels.
Average milksolids over the three treatment groups for the whole lactation were similar to or greater than the average for the rest of the herd not used in the trial.
DairyNZ advice is that when faced with missing milkings it’s important to sustain feeding levels at pre-disruption levels if possible to not trigger the drying-off response.
Obviously, at times this can be difficult in the face of adverse events like flooding or snow, but if feeding levels drop it can be harder to get cows back to full production.
SCC is the other worry when having to miss milkings. In the WTARS trial, average SCC spiked to two million cells/ml over all three treatment groups at their second milking after the disruption period. It was suggested this was largely due to a “concentration effect” – the same number of somatic cells were being produced but because milk yield was at its lowest at the second milking, there was less dilution so SCC jumped.
The two- and four-day treatment groups were below the 400,000 cells/ml grading penalty threshold within six milkings (three days).
The seven-day treatment took five days to get back to below the grading level and three of the 12 cows developed clinical mastitis.
In the trial write-up, the scientists involved warned that in commercial herds the elevation in SCC and incidence of mastitis could be greater than that observed in this experiment as the cows selected were tested as being free of mastitis-causing bacteria.
Referencing research undertaken to investigate the impacts of switching to once-a-day milking, Lacy-Hulbert said the elevated SCC is an unavoidable physiological response.
“The cow is used to being milked TAD, so the production and release of those cells has got used to the milk disappearing every 12 hours,” she said.
Missed milkings are likely to have more impact if they occur in early lactation, particularly in the first three weeks. Lacy-Hulbert said the disruption to milking frequency, experienced at a time when the animal’s whole immune system is compromised as a part of a physiological response to calving, made cows particularly susceptible to clinical mastitis.
