I have seen programmes on TV where rams have some form of paint dispenser fitted to their underside before being put to ewes for mating. This dye then is transferred to the back of the ewe during mating which indicates to the farmer that 'the deed had been done!'. I assume that this dye is waterproof 'cos otherwise it might wash off in the rain. That being the case, how come that sheepskins you can buy in the shop are 'dye-free'? I know the skin is washed as part of its preparation toward going on sale - but does this remove the dye? Is it not waterproof afterall?
According to a sheep breeders' website, dye isn't used (via a straddle or by applying it to the ram's fleece) where 'wool is important, as the dye can't be removed' and in that case they just 'assume the deed has been done'!
My grandfather used to be manager of a wool factory where they processed the wool straight from the farms before sending it on to be spun. The workers used to hand pick bits of dyed wool, droppings, matts etc out of the fleeces, leaving them ready to be further processed. This was only about 20 years ago and he gave me a tour round the factory for a school project, so I imagine it is still done in a similar way.
I once asked a local sheep farmer about this.
His explanation was this.
The colour in the block only lasts on the back of the ewes for about 3 or so weeks before it fades or is washed out by rain.
As the ram is only in the field during the time when the ewes are in season the farmer looks every day so see which ewes have been mated.
He then puts the mated ewes in a seperate field.
So as you can see the colour only really needs to last a few days,as during the ewes receptive time the farmer is constantly checking on which have been mated.