Cows are very fond of rhythm and regularity.
They have an excellent sense of time. Turning back the clock results in a temporary disruption of the daily rhythm for some cows, (as for some people).
As a result of the shift in the daily rhythm, some cows can temporarily give up to 10% less milk. The more milk the animal gives, the more likely it will respond to the time change. The recovery from this production decline varies greatly per animal and per farm.
Fortunately, it is usually limited to a few days. In exceptional cases, the animals will only return to almost their original production level after one to two weeks.
I consciously write “almost” because with a production decrease of 10% the recovery is often limited to an increase of 8 to 9%.
TRICK CAN MINIMIZE THE DAMAGE:
By not making a one-hour jump but a 30-minute step, you reduce the effect for the cows.
After two days you have also realized the time difference. This is not only more pleasant for the cow, but often also for the farmer.