Well, it depends on what kind of meat chickens you want to keep. Here's a rundown of the types of chickens:
- Laying fowl. Lots of different breeds that class as laying birds. Hens are good layers, but they are usually not very heavy in body, so not very good meat birds. Physically mature at 20-24 weeks of age (5-6 months). These birds will run, roost, scratch, fly, and forage like one expects a chicken to do. Requires a 16% protein, 3-5% calcium laying crumble or pellet.
- Dual purpose fowl. The hens are good or decent layers, and both hens and cocks show a decently heavy or stocky body. Lots of breeds that fall into this class, but most of them would only be good for meat (in addition to eggs) if purchased from a breeder, as hatcheries have bred most of them down in size so they can emphasize their laying abilities. The best dual purpose fowl I've found are Standard Cornish, English-style Orpingtons, and Naked Necks. These breeds can physically mature anywhere from 20-52 weeks of age. Naked Necks will be on the lower side of that scale whereas Cornish and Orps can take a long time to mature. These breeds will all run, scratch, fly, forage, and roost like one expects a normal bird to do; the exception would be exhibition-style Standard Cornish, some of whom may not roost and generally cannot fly much, due to their extreme body type. Technically require a 16% protein, 3-5% calcium laying crumble or pellet, but because they all show heavier body types than the skinny Leghorns that commercial laying feed is formulated for, they also wouldn't be bad off being fed an 18% protein, 1-2% calcium grower crumble, supplemented with crushed oyster shell for the hens.
- Slow growing broilers. There are a few different birds that fall into this class, common ones being Red Rangers, Red or Black Broilers, Slow-Growing Cornish Cross, and some strains of meat-emphasized Naked Necks, among others. These are mostly meat birds, but some hens can be pretty good layers. They are physically mature at 12-16 weeks of age, but will often continue growing on into 20 weeks of age if they are not butchered younger. These birds will scratch, run, fly, forage, and roost, but because they are quite heavy and grow rather fast they may not run as fast and tend to get tuckered out sooner than a normal chicken. They also may not live as long, since a lot of strain is put on their organs and joints - I wouldn't peg them as living past 8-10 years, barring death by predator or disease. These birds would do best started on a 20-22% protein, 1% calcium starter ration, and can be switched to on an 18% protein, 1-2% calcium grower ration starting at 8 weeks of age.
- Broilers. These are what the meat industry uses. There is only one breed (technically hybrid) of fast growing broiler, and they are known colloquially as Cornish Cross or Cornish Rocks. There are many strains and subsets within the breed, but for the intents of someone simply wishing to raise a few meat birds, those aren't relevant. These are meat birds only, and are not for use as pets, laying fowl, or breeders. They are mature at 6-8 weeks of age, and although they can be kept longer, it's not recommended. They are very prone to health issues if raised past butchering age, mostly joint and organ issues, and many will succumb to death prior to reaching mature size (often 12-18 pounds and sometimes over 20). These birds are not known for being particularly active; as a general rule, they will not run, fly, scratch, roost. or forage. They may engage in these activities occasionally (the ones they are physically capable of), but they will spend most of their time lounging and sitting. They require a high protein feed, 20-22% protein and 1-2% calcium.
Some things to consider when choosing between the different types:
- Money and time. Dual purpose birds will consume a lot of feed and require more care since they will be alive for significantly longer than any broiler. Slow growing broilers will consume less feed, but will still be around for a good amount of time. Fast growing broilers are the most economical option; they will seem to eat tons of feed, but in the long run they still eat a lot less feed than either slow growing broilers or dual purpose fowl, since they grow so quickly and waste little energy. They also require less care, since they are not around very long.
- Breeding. Do you intend on producing your own meat birds? Dual purpose fowl can breed and reproduce normally. Slow growing broilers can reproduce, but I would caution keeping the cocks around any breed besides broilers, as they can get extremely large and are prone to crushing smaller hens. Cornish Cross should not be kept or breeding attempted, and cocks are unlikely to be capable of reproduction anyways; they are simply too heavy and awkwardly shaped to mount the hens.
- Flavor. Dual purpose fowl will taste quite different from any grocery store chicken you have ever had; hens and pullets will be very flavorful, and cocks and cockerels will have a dark, gamey taste. Most people tend to like the flavor of hens, but many dislike the gaminess of cocks. Slow growing broilers will taste similar to grocery store chicken, but pullets will have a bit more flavor, and cockerels may begin to develop gamey flavor starting around 12 weeks. Cornish Cross are grocery store chickens, but when they are home raised they are usually described as tasting like the best chicken you've ever had.
In response to your actual question:
- Dual purpose chickens and laying hens can be fed the same rations throughout their life. Both types should be started on a 20-22% protein, 1% calcium starter ration, switched to an 18% protein, 1-2% calcium grower ration at 8 weeks, and put on a 16% protein, 3-5% calcium layer ration at 16-18 weeks.
- Slow growing broilers can be fed the same rations mentioned above for dual purpose and laying fowl, but would grow better if kept on a 20-22% ration until 12 weeks rather than 8.
- Fast growing broilers should be kept on a 20-22% protein, 1-2% calcium ration from 0-8 weeks/butcher age.
- Feeding a broiler fowl - either slow or fast growing - a layer feed would be very bad. The lack of protein would result in poor growth, and the excess calcium can cause lots of damage to their already stressed organs, mainly their kidneys.
- Feeding a laying fowl a broiler ration is not likely to hurt them. The additional protein is unnecessary in their diet, but excess protein typically cannot cause organ damage until seen in levels 30% and usually higher. The hens would need to be supplemented with free choice crushed oyster shell. It is not recommended that laying hens are fed this diet year round, as it isn't necessary, but the chances are very low that it will actually hurt them.
So, if you are raising dual purpose fowl, they can eat the same feed as your laying hens. Slow growing broilers would do best on a grower/broiler ration for the majority of their growing period, but this feed won't hurt the laying hens, especially short term. Cornish Cross should be fed a grower/broiler ration life long, but similarly, this feed won't hurt laying hens.
