Shedding is an interesting and important attribute of the Dorper sheep. It is affected by genetics, climate, nutrition, age of the sheep and type of cover. A fluffy, light loose cover will shed better than a coat that is either wooly or hairy. A lamb will not express its full shedding capacity in its first summer.
The shedding in a breeding up program will depend to a large extent on the original sheep breed. The Merino , for example will need to be at least 4th cross before total shedding is achieved, though after the second, few will need crutching and bellys will be light. Starting with a White Suffolk will give very good shedding after the 2nd cross, and this should be similar for a poll dorset, and believe that the Texel produces shedding on the first cross.
This is a bit of a generalisation and there are always exceptions to the rule, we have a few fullbloods with poor shedding, but this is now a rarity in the flock.