In Breeding - Intentory list you can see a list of the breeding stock you have created. Here you can also see how many of them has been removed from the inventory, meaning animals that has been discarded. Then you have the number of breeding stock in the stable. Note that the "Sold breeding stock" is all the animals that has left the herd, both slaughtered and sold, here animals sold through a delivery note and those not sold through a delivery note is included. 

Then the number of animals you have made delivery agreements on or created are shown. This gives you the number of available animals, that you can create delivery notes on. If you have chosen extra animals for a delivery note that these are shown in a seperate line. The line "Breeding stock available" shows how many animals there is to choose between. All of this is divided in Age in weeks and Birth week.