The Myth: Incomplete milking leads to mastitis...
Busted: It's fiction!
There is a long-held belief that leaving milk in the udder will lead to mastitis.
Indeed, housewives in England in the early 1600s were exhorted to not ‘leave a (house) cow half milked’. But research as early as the 1950s indicates that, for cows that are normally machine milked, residual milk does not cause mastitis.
The topic has received recent attention with the promotion of strategies such as maximum milking time (MaxT) or increased automatic cluster remover (ACR) threshold, to reduce cow milking times and increase milking efficiency. See dairynz/milking.
In five recent trials in New Zealand, the effects of MaxT and increased ACR thresholds were examined.
These showed no increase in mastitis, or decrease in production despite, in some cases, leaving strip yields of more than 0.7 litres. These studies used cows, milked twice-daily, with
relatively low somatic cell count (SCC).
Previous Australian work concluded that incomplete milking, in their case leaving behind 0.5 litres, did not cause a detectable increase in SCC for cows with mild subclinical mastitis. Therefore, a higher SCC should not be an issue for farmers wishing to shorten cow milking duration.
The effects of gross under-milking have not been well researched, and the long-term consequences of leaving more than a litre of milk behind at each milking are unknown.
Once-daily milking, whereby 100 percent of the evening milk is not harvested, could be considered an extreme version of undermilking, although it does not involve opening the teat canal.
Once-daily milking typically causes an increase in SCC and leads to a 10 to 30 percent loss in production per cow, depending on timing and duration, but generally does not increase the risk of mastitis. Therefore, it is unsurprising that no increase in mastitis or production loss has been reported with the relatively small increases in strip yield when using MaxT or increased ACR thresholds.
Of greater concern is the risk of over-milking, which occurs when attempting to extract every last drop of milk from the udder. This can lead to teat-end damage. Over-milking may also
increase the likelihood of transfer of infection between quarters during the period of little or no milk flow. Consequently, overmilking should be avoided.
So, after nearly 400 years, it may be time to put this myth to bed. A moderate level of incomplete milking (e.g. strip yields of up to 1 litre of milk per udder) does not increase the risk of mastitis.
by Jane Lacy-Hulbert, DairyNZ Senior Scientist and Paul Edwards, Post-graduate Student
This article was originally published in Inside Dairy September 2013