Most of Grameen Bank's borrowers use the small loans to start businesses by, for instance, buying a cow to produce milk, or a rickshaw, or materials to make cloth or pottery.
Cows produce milk perpetually.
You can only milk a cow at certain times before they can no longer be milked. This could not be gleaned from the excerpt, but is common knowledge.
( z1 produce :ARG0 ( z2 cow ) :ARG1 ( z3 milk ) :duration ( z4 perpetual ) )