In my area (and most areas I would imagine) alfalfa is much cheaper than grain. I plan on raising mangalica pigs which historically in Hungary were fed on just alfalfa and barley. I also have read that alfalfa is one of the best feeds for pregnant sows. I also know in general heritage breeds can live almost entirely on forage if given the space and climate.
I plan on supplementing their diet (especially when in season/before meat harvest) with crabapples, chestnuts and acorns, as well as other fruit and nuts.
My question is how much alfalfa can I feed without losing meat quality or gains? Can I feed 50 percent of their diet for the first few months on alfalfa? Can I feed more than that? How much alfalfa is too much?
Interesting question. We pretty much free-ranged our pigs and fed them on scraps, so I never looked into alfalfa as feed for them. But I do feed it to my goats. Alfalfa is a legume and has different nutrients than grains. Alfalfa is rich in protein and calcium, while grains are high in carbohydrates. I know corn alone isn't recommended because it contains little to no lysine, so you end up with lysine deficient animals. I don't know which amino acids are prominent in alfalfa, but the combination might balance the nutrients. You might want to consider a combination of the two for nutritional balance.
We have mangalitsas. Foraging on ample natural foliage + eating fermented grains, our sows were just 150lb~ going into their first winter at 9 months old. At 2 years old now they're maybe 450lbs. They love foraging and will happily feed themselves if at all possible. However, they're a notoriously slow growing breed.
For example, their piglets this summer, who were half hampshire, were 200-250lbs at 4-5 months old. The hampshire boar who fathered them exploded from 600lbs to 1,000lbs in 4 months, at which point we had to butcher him at just 2.5 years old. I would anticipate our mangalitsas taking 3-4 years to reach 1,000lbs.
I don't think you can grow a mangalitsa to 200lbs in their first season now matter how much food you offer. We weren't "trying" to grow our sows since they are our breeders, but they still had virtually free-choice feed, and they did grow faster than manglitsas are "supposed" to grow, reportedly averaging just 150lbs~ at a year old.
They do love to eat hay, even grass hay. That's what we supplement alongside grain and forage. So I couldn't say anything from experience about alfalfa.
Here's some fun photos of our pig experience. We liked the idea of mangalitsas BECAUSE they were supposed to be slow-growing, and since we wanted sows as breeders, we didn't want the out-growing us too quickly. We liked the meat pig cross piglets so they grew really fast. The mangalitsas are active and not prone to sitting in front of the trough and eating endlessly, like the production meat breeds. They have very petite appetites and love to run, play, forage, and expend energy.