I am developing a hybrid poultry grazing model that attempts to incorporate aspects of the Salatin tractor model and the coop + free-range electronet paddock layout. It is inspired by the ideas presented by Forrest Pritchard in this article--
http://smithmeadows.com/farm/mob-grazing-with-chickens/ His system adapts a "hub" or "wagon wheel" model to work on pasture and with some subtle details that make it more functional and resistant to hawks and other aerial predators.
Two arguments in favor of Salatin-style tractors and against free range is that the latter is too vulnerable to hawk predation (it might work for a year or two, but once they discover your chickens it's all over!) and also creates a less significant mob grazing effect. Pritchard solved these issues by utilizing a "free range" system that is very densely stocked and evenly grazed, but that is not vulnerable to hawks. He does this by laying out rotational grazing alleys in very narrow strips of electronet. Hawks get freaked out by the tight fencing and will not try and land in the lanes.
This system is obviously a compromise on the real "free range" experience that a larger open paddock would create, but the chickens are still better off not being being cooped up in 2ft tall tractors. Also, since a tractor covered with chicken wire or (more likely if you have much predator load) hardware cloth tends to block out larger insects, such as grasshoppers, tractor chickens suffer reduced foraging ability. But, on the other hand, Salatin points out that too much space leads to "too much movement" that just burns calories and causes a reduced feed to weight gain ratio on broilers. I think that Pritchard's system offers an excellent compromise in this regard.
A final point to consider is that, not only is electronet a very good 24/7 deterrent to predators, but it keeps a wider buffer between predators and the chickens than a tractor or coop alone. Possums and raccoons are great at reaching through chicken wire and the birds, especially on hilly terrain, will tend to bunch up against the wall making them that much easier to grab. Electronet prevents this concern and also allows for the design of much more functional coops that can have larger wheels with better balancing, without a concern for predator entry. I have always hated dragging around clumsy and poorly balanced chicken tractors and having to ensure that you don't set it down on any dips or ruts that would allow predators to slip underneath. So, not having to rely on a tractor pen as the main line of defense is a real plus.
That said, I do find fault with Pritchard's design for a couple reasons. Firstly, I dislike a coop that remains stationary for more than a night. He ends up having to add bedding and has a "sacrificial zone" after a few weeks where the pile of deep litter has smothered the grass. Also, chickens drop the majority of their manure at night, so not moving their sleeping quarters daily defeats a major motivating factor for keeping them on pasture (spreading the manure evenly). My second major modification to his system is that my land pasture is mostly on a hillside and I want the chicken lanes to always run on contour, across the slope. Accommodating these concerns has
led me to the following design, which takes the advancements of Pritchard over Salatin, but then adds back in some Salatin--
The following layout will accommodate around 1,000 birds. You could scale up to this from 40 birds or go up to about 1,200 before it would be full maxed out. At 1,000 it is a somewhat lower stocking density than Salatin uses in the same area. My reasoning for choosing this size area has to do with my already established grazing system. In the growing season, I move our sheep and cows every 3 days or so in 50'x100' paddock cells, so I wanted to design a chicken rotation that could mate with the current move schedule. Following the chickens immediately after the ruminants is both the most convenient arrangement for me (shares the same perimeter fencing) and the best practice for the pasture (pasture gets the maximum amount of rest and minimal "shock" from re-grazing) and animal health (the sooner they scratch through the manure, the fewer fly larvae will be able to hatch).
Since my current grazing setup is 50'x100' cells, the chicken lanes are designed to comfortably use my same 100ft and 50ft lengths of electronet. I know for sure I won't set this up in perfectly straight and square lines, so I imagine the lanes varying somewhat between 6-8ft wide. There are six chicken lanes and the ends of the whole area are capped with a single length of 50ft netting (reused from the sheep and cows). This means that each grazing strip for the chickens is approx 700 sq ft and will keep about 180 birds for 3 days. I need six of these strips at a time to fill the 50'x100' area and keep pace with the rotations.
The chickens will have three mobile "coops" per grazing strip, for a total of 18 "coops" in the whole system (at maximum capacity). Each "coop" is 6ft wide x 10ft long x 2ft tall (60 square feet of ground space). These look similar to a tractor pen, but with pass-through chicken doors on either side that stay open. They are only intended for sleeping and daytime
shelter during inclement weather and when the chickens need to be cooped up for processing, etc. I will weld them from steel tube stock to be sturdy but lightweight and attach permanent, relatively larger wheels to them for easy moving.
Since the perimeter
fence will already be established from the previous livestock, this system will "only" require setting up 5 sections of 100'
fence every few days, plus the time to move the 18 coops every day. It takes me about 10-15 minutes per fence section, which when added to the time to refill water and feed troughs and roll the dozen coops forward, the whole operation should add approximately 3 hours of additional farm labor, spread out over the 3 days in each paddock cell. That really is not so bad for 1,000 pastured chickens in an intensively managed free range setup! I hope to test out this system in the spring with a single run and will see how it goes in real life. Any suggestions on modifications or potential problems would be appreciated.