Line-breeding is the breeding together of loosely related members of family groups within a breed population. It uses multiple forms of the axiom breeding, “Let the sire of the sire be the grandsire of the dam on the dam’s side.” This is the most frequently used form of inter-family mating. It is relatively safe in that it does not encourage a large number of birth defects, and if well done, it can produce quick improvement in multiple aspects of breed specific conformation and temperament development.
Within the line-bred system, balancing the family relationship relies heavily on very close study of the pedigrees within the line. Conformation improvements and regression of line characteristics are all controlled by continually balancing the relationships of family members to keep the familial relationships static or rebalancing those relationships to eliminate or accentuate desirable conformation and temperament features. Line-breeding improves consistency of type within the littermates and enhances traits considered valuable within that bloodline in most instances. When defects arise, they must be dealt with by rebalancing the line and breeding away from the defect.
Equally balanced family relationships on either side of the pedigree shared between the mated pair serves to maintain the status-quo of the line-bred family. It introduces few new genetic factors and reduces the influence of breed characteristics not already carried within the bloodline. Only when an undesirable character or defect enters into the get and requires correction need that balance be interrupted. Too close line-breeding may reduce breeding vigor within the line after many generations, but this can usually be readily re-established with occasional outcrosses to another line.
Backcross line-breeding is a technique sometimes used to bring out superior characteristics of one or more ancestors within a line. This system takes even more careful pedigree study and percentage calculation by the breeder. However, skillfully done it is the most productive form of line-breeding to bring out exceptional improvement in multiple get of a single breeding. In backcross breeding, one or more ancestors are singled out and emphasized by duplication within the pedigrees of the mated pair. Backcross breeding tends to bring forward the phenotype of the ancestor in the immediate get of the litter, but the breeder must be able to spot that type within the litter and then select for that type in subsequent breedings to make this a successful technique. Backcrosses sometimes require two or more rebalances of the cross with subsequent mated pairs to attain the desired results.
When breeders speak of establishing “Their Line” within a breed, they are not often referring to a line-bred breeding system. Most frequently they are discussing establishing their personal kennel name on a family group within their breed, purchasing foundation blood stock, and startup of a breeding practice no matter to which breeding system they ultimately subscribe. Unless the individual has tons of experience in breeding, they do not usually set out to create a workable long range developmental plan at inception of establishing their “line”.