"Foundation stock" refers to the original breeding animals or plants used to establish a new breed or variety. It is the starting point or the base from which a particular breed is developed. Full definition
I like it as good foundation stock that throws off a lot of cash with the high yield. (moredividends.com)
When these efforts are combined with pedigree analysis, the results will yield quality foundation stock whose offspring can be saved to further improve a breeding program. (champagnekennels.com)
It was at this stage that an American, Roswell Eldridge, began to search in England for foundation stock for Toy Spaniels that resembled those in the old paintings, including Sir Edwin Landseer's «The Cavalier's Pets.» (ckcsc.org)