You may already know all this, but I’ll include it anyway so you know what to expect when you have mature hens and a mature rooster in your flock. This is between mature consenting adults. Immature chickens, especially cockerels, are different. It can get pretty wild.
Typical mating behavior between mature consenting adults.
The rooster dances for a specific hen. He lowers one wing and sort of circles her. This signals his intent.
The hen squats. This gets her body onto the ground so the rooster’s weight goes into the ground through her entire body and not just her legs. That way she can support a much heavier rooster without hurting her legs.
The rooster hops on and grabs the back of her head. The head grab helps him get in the right position to hit the target and helps him to keep his balance, but its major purpose is to tell the hen to raise her tail out of the way to expose the target. A mating will not be successful if she does not raise her tail and expose the target. The head grab is necessary.
The rooster touches vents and hops off. This may be over in the blink of an eye or it may take a few seconds. But when this is over the rooster’s part is done.
The hen then stands up, fluffs up, and shakes. This fluffy shake gets the sperm into a special container inside the hen near where the egg starts its internal journey through her internal egg making factory.
You’ll notice that the hen squats. That gets the weight into the ground through her body, not her legs. Roosters are normally bigger, sometimes quite a bit bigger, than hens of the same breed. Some people keep bantam hems with full sized roosters and don’t have any problems when they mate because of that squatting. They are living animals so I can’t give you any guarantees. Plus the more difference in size the easier for something bad to happen, but personally I would not worry about a Brahma rooster and that hen.
This has come up before so I’ll clarify it. I really don’t know how much you already know so please don’t be offended. A rooster does not have a male part that penetrates the hen. He fertilizes the eggs by touching vents, no penetration. The risk is from the weight of the rooster when he is on top of the hen.
A Brahma is a large chicken but they are slow to mature. The cockerels are mostly bones until they hit a maturity level where they finally start putting on meat. If you plan to butcher at a relatively young age they may not be the best choice for your goals. People do use Brahmas for meat so it’s not an awful choice, but you may be better off getting a smaller rooster that puts on meat faster.
When you add a cockerel to a flock of mature hens, the hens sometimes are pretty vicious toward him until he matures enough to take over his flock duties. Same when you raise a male chick with the flock after he hits puberty. Sometimes as he matures but before he reaches maturity he can be pretty forceful. It doesn’t always happen. I’ve raised cockerels in a flock of mature hens with no mature rooster and it has usually gone really peacefully, it actually usually goes without a lot of drama for me but I have a lot of room. I think that makes a big difference. Still, I have seen drama and if you read through this forum, lots of other people have too. I think you are better off adding a mature rooster who will immediately mate a hen or two to show he is boss and just take over the dominant position.
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I raise my cockerels with the flock, usually with a dominant rooster running the flock. Sometimes there is drama, but often not a lot. Lots of people successfully raise males with a flock of mature hens with or without a dominant rooster in the flock without a lot of drama but the cockerel’s adolescence can impart a lot of drama. Again, not always. There is some luck involved.
Probably a lot more than you wanted. Good luck on the move.
]); so how valid are results even for whole/entire birds of the same inbred production breeds, based on tests on birds who lack that part of their digestive system, one wonders? I could go on, but I'll spare you another rant on that topic 
