Most people would be familiar with a traditional rectangular, pasture paddock, bound by three strands of electric or plain wire, with a water trough in one corner, and a shelter.
We choose to have at least two horses in each rectangle paddock, but many horses out there in the world are kept in a paddock like this on their own. It's most suitable for horses that are exercised (ridden) every day. The advantage is that they are where you left them, they are generally clean, with no bites and scratches, or other injuries. You can pretty much guarantee that if the feed bin is empty, that one horse ate what was in it. It allows you to quarantine horses in cases of injury, contagion, or solitary confinement for aggressive horses.
There are two problems with this system. The first is in terms of management and resources. If you have nine paddocks, you need nine shelters, and nine water troughs, and nine taps, and nine gates. You have to carry nine buckets of feed out to nine feed bins. You have to clean nine paddocks, and if you have a weed in your hay, then it is spread across your whole property. Having a separate paddock for each horse is the most expensive and time consuming way to allocate resources.
The second problem is that most horses out there in the world are not ridden every day. Of the hundreds of horses that we see in our nutrition and hoofcare consults, there are probably only a dozen that are genuinely ridden every day. Many, many riders keep their horses this way because they intend to ride the horse, except then it rained, or it was windy, or it was too hot, or you had to go in to work early. If you count how many times you hosed off a sweaty saddle mark over the last month or two, that will give you a closer idea to how much you are actually riding. These horses end up parked in the corner of the paddock doing nothing at all, day after day, with no opportunity to mutually groom. It's not living like a horse, and it's not having a purpose in life. It's like long term unemployment for horses, which is not really good for their physical or mental health long term.
Many people who can't afford to, or who have not yet got around to setting up separate shelters and tubs for each separate paddock might be using an equi-central system by default. With equi-central you have your shelter, your water, and your feeding area in the one location. You then set up your turnout - usually by having gates on to a central corridor, so that horses (who are generally run together) can access this central location regardless of which paddock they are in. Both equi-central and paddock paradise are suitable for horses that in reality are not ridden every day - which is most horses.
The advantage is that you are using resources very efficiently. You only need one shelter and one water trough. If you set the feeding area right outside your feed shed, you're not lugging feed over long distances. If you establish a routine, the horses will usually come to you (often very promptly and at speed). It allows you to rotate paddocks very effectively, and if you have a weed in your hay, it is only in one discreet area. It is a more natural situation, because the horses move in a herd, and they move around a lot more. It's an excellent way of managing a property if you really only want to divide the property into two or three paddocks.
The problem is that it assumes all your horses get along and have the same requirements. If you put out five different feed bins, they are likely to swap and the slow, or most timid horse may not get anything. Also, if you have no routine, then you might have a very long walk to collect horses from the very farthest corner. This might seem like a small thing but many horse owners set up their property to minimise how far they have to go to get the horse.
The big thing is that this is most likely set up to induce laminitis or founder. If your horse is a TB with flat feet, a fat pony or a quarter horse, then unrestricted access to abundant turnout like this can be a problem. It's also a cumulative problem. Horses that can cope with (and even thrive on) abundant pasture initially may start to develop seasonal bouts of subclinical laminitis, and then insulin resistance and then eventually Cushings. Some people use this system, but bring their horses into a smaller paddock overnight (what is generally referred to as the 'Jenny Craig paddock'). This can be a very effective way of managing laminitis.
Paddock paradise (based on the study of wild horses by Jaime Jackson) has the advantages of equi-central without most of the drawbacks. Paddock paradise is like strip grazing, but in a loop.
It means you can combine resources, and run horses together, increase movement and but also limit access to pasture. The two great advantages is that the horses really travel a lot in paddock paradise, and they travel at speed as well as just walking. You can also have complete control over what they are eating without having to limit movement (the 'Jenny Craig paddock'). The main source of forage in a paddock paradise system is hay, which can be expensive. Not as expensive as keeping a lame horse.
Having experimented with this for a few years now, we've come up with some basic principles.
* The run should be at least twelve paces wide. It helps to have some wider places, but not narrower than twelve paces.
* Electric fencing is better because if it breaks it is easily fixed and there are no injuries.
* Set up your design first with pigtail posts and electric so that you can alter it once you see how they use the space.
* Five is probably the maximum number of horses you want in a single run. Three of four is ideal. If you have one horse they will tend to park, unless you have another horse in the centre of the loop.
* It helps to round the corners, because they will often gallop, and it helps to guide them around the bend.
* You can place gravel or sand or obstacles (we use split posts) over high traffic areas to reduce dust and mud and to passively condition hooves.
We have found all three systems to be useful in different circumstances. If we should get some rain, and the pasture began to grow, or we are riding more, or they are gaining or losing weight, we manage them differently. It's about flexibility, and adjusting the circumstances to meet the requirements of the horse standing in front of you.