Astrain is a certain family of birds that are usually bred with a certain emphasis on specific traits.
For example, a breeder of utility Light Sussex chickens, bred for meat and eggs will want to select birds that lay as many eggs as possible and produce a good weight for the table, a breeder wishing to show Light Sussex will select birds with the right comb and markings for his or her breeding flock.
Breeders develop their birds for many different things though, not just egg numbers. The colour of eggs (Marans for example lay very dark brown eggs), body weight/size, and of course the appearance to meet the various poultry standards, especially if birds are going to be taken to show.
Commercial strains of birds (that can be hybrid birds, not just pure bred birds) are usually given specific names after the producer, or after the cross. The Black Rock hybrid is an example. Whilst it is possible to cross the same pure bred birds (Rhode Island Red and Barred Plymouth Rock), the strains that are being crossed are not the same and it is the characteristics of these strains that give the Black Rock its well-known characteristics. You cannot buy Black Rock hatching eggs by the way so you need to find pullets from one of the dealers that grow the chicks on.
Our Poultry For Sale (UK) database lists breeders by region and details the breeds they should have available.
So next time you decide to buy a certain breed of bird, don’t just consider the nearest breeder, try to find out if that breeder’s birds have the qualities you are looking for. This is especially true if you are looking for a cockerel that is suitable to keep with young children around. Whilst certain breeds of fowl tend to be more aggressive (See the article on assessing the temperament of a cockerel with children, certain strains of any breed can be very aggressive. I once purchased two different strains of Light Sussex and found the cockerels from one strain very aggressive and totally unsuitable for me to keep with young children around whereas the other strain of cockerels were completely the opposite and were incredibly friendly towards the children. A little research with the breeder would have paid off.