Farm-workers milked cows by hand.是什么意思？

Farm-workers milked cows by hand.

农场工人用手挤牛奶。

milked

v. 产奶，挤奶( milk的过去式和过去分词 )，榨取，勒索；

例句
In the natural course of events cows would wish to be milked more than twice a day...
按照事情发展的自然规律，母牛每天应该挤奶两次以上。

cows

n. 母牛( cow的名词复数 )，雌象，婆娘，娘儿们；

例句
When his cows calve each year he keeps one or two calves for his family.
他的母牛每年产犊时,他都给自家留上一两头。

by

prep. 在…旁边，表示方式，由于，经过；adv. 经过，表示保留或保存时用，短暂拜访；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

hand

n. 手，协助，帮助，（工具等的）把，柄，掌管；vt. 传递，交给，搀扶，支持；

例句
His hand brushed against hers; it could have been either accidental or deliberate.
就在有意无意间，他的手轻轻拂过她的手。