IMO some fanciers darkness youngsters fail as yearlings because they pair them up to early. If you look at a darkness youngsters life, in a 8 month span they body moult twice, are trained & raced covering a total of well over a 1000 miles (heavy trainers nearer 1500) in-between moults. Fanciers that pair them up early do so in many cases whilst they're still growing their last flight. I feel in these cases the darkies haven't benefited from rest & time to get into breeding condition before they're asked to raise a pair of babies, (They say that breeding a pair of babies is equivalent to a 500 mile fly). IMO pairing them up the end of January is plenty early enough.