The standard for goats is 305 days with 2 months off beforet he next
kidding. However, some goats -- especially high-producing Saanens can
be milked straight through for two or even three years.
Note about cows: When I was a kid we had a brown swiss that we milked
for more than 10 years with no calves.
Goats need to be milked at least one a day; some dairies milk 3X. The
more you milk them, the more they produce (and the more they eat).
A dairy cow can easily raise a couple of calves, even if she is milked
once a day. As Lynn says, you have the keep the calves away from her
at least overnight.
Marie
[Homestead] Dairy goat lactation period,
Marie McHarry, 11/17/2008