Here's a quick run down of the dairy operation.
The cycle I am shooting for is seasonal and is usually geared towards having a cow in milk when the grass is growing vigorously. Another factor is that it is harder on a cow to be in milk with the heat of summer, so there are opposing advantages as to when you keep your cows in milk in Florida.
A heifer can be impregnated for the first time as early as 15 months. The gestation is 9 months so a cow would start producing milk at 24 months at the earliest.
Once a cow has calved, you usually leave the calf on to consume colostrum the for at least 24 hours...some leave them on for a week or more. About 2 to 3 months into milking you aim to impregnate your cows. Milking continues until 2 months before the calf is born (7 months) and then she is "dried-up" to focus her energy on developing a healthy calf.
The goal of this system is to create a one-year cycle, and having your milk production tied to availability of forage or weather...as I mentioned above, these are different times in Florida.