Here is an exerpt copied and pasted from the link I posted in my earlier entry above.
PROBLEMS CAUSED BY (K) OR (t) SLOW-FEATHERING GENES
It is advisable to remember here that once adulthood, i.e. sexual maturity, is reached there is no difference in plumage between the various subjects whether or not they are affected by this phenomenon. Sorting between them becomes impossible after this age and often even much earlier.
We have to thus make a type of selection made easier at hatching. Simply eliminating the young chicks locatable by difficult fledging, in particular on the tail, the back, and the wings would make it possible to obtain a rather easy cleansing of the stock over a few years.
In addition, since during expositions or shows, it is not possible to distinguish the subjects concerned as they are adults, then we are very tempted to think that these types of reducing genes do not present major disadvantages. In fact, the risk exists of a real and lasting laxity in regards to selection for breeders from this point.
It appears then that these types of slow-feathering genes of the young chicks, which are of course hereditary, not only do not bring anything positive to the breed but especially can cause some problems.
Thus, it was discovered in 1988 that the Asian slow-feathering gene (K) in particular would be in close connection with the existence of an endoviral gene of the viral family which causes leucoses. The subjects with the slow-feathering gene (K) would be thus more sensitive to this group of diseases and have proven to have reduced performance.
In addition, slow or late feathering makes it obvious that these young subjects are more sensitive to picking, having their back stripped to at least four weeks of age and especially, their puny tail feathers which are not very hard at the base until at least eight weeks of age.
Let us recall that at this age, the normal subjects have their caudal feathers entirely finished.
We must still stress that the subjects with slow-feathering genes show after slaughter a more significant number of pinfeathers than normal subjects.
Lastly, we must add that the young Marans pullets with normal and rapid feathering tend to begin laying earlier. To contrast, allele (K) might, however, make it possible to support a greater clarity of barring in the Cuckoo plumage, or even of the intensity of the red in poultry plumage.
In spite of the probability of this attraction, which remains to be shown at a greater length, these types of genes are proving more or less handicapping and rather not easily identifiable between them. Consequently, it seems quite obvious, as far as possible, to limit if not eliminate all the young Marans subjects which present one or another of these reducing genes.
