I breed Bernese Mountain Dogs on a small scale.
We'll have two litters at the very most/year; next year will be the first time we have 2 litters (one litter from each bitch). We kept a puppy from Callie's first in Sept. '07. and last litter from May '08 so that in two years we'll retire Callie (after her having had 3 or 4 litters). Next year she'll be bred along with the female we kept from her first litter (Heidi). And then the year after that she'll be retired and Heidi and Katie will each have a litter etc... We'll rotate like that for a bit and then quit as we're keeping Callie once she's retired etc...long story.
And, yeah, we make a bit of money from them, but it's not for the sole reason of being able to make money for the horses. Although pups are sold for $1200. You're factoring in food, microchipping, registration, vet-checks, Advantage/Revolution, worming, vaccinations, etc. You've got to lop off at least $200/pup for stuff like that. Also, it requires a lot of work, worry, and patience. Not only with the pups themselves, but in finding good homes for them. I can't imagine having the time to take care of more than two litters per year. After they're 3 weeks old and starting to eat solid food, it's pretty much their world and you are there butler/babysitter. Mom pretty much says, "Oh, thank God! You can take over from here"
I'm so not kidding. So, although rewarding, it can also be tiring and stressful. Nevermind the very real risk of infection, death of pups and/or the mother etc. Make sure you know what you're getting into...
Oops sorry. I see that you've bred dogs before and are just asking for curiousity's sake.