Inbreeding of and Relationship Among Registered Holsteins

Holstein-Friesian Herdbooks (Holstein-Friesian Association of America, Brattleboro, VT) were used to draw random samples of 600 registered females born during each of the yr 1970, 1976, and 1982. A two-line pedigree, one random line of ancestry tracing from the sire and another tracing from the dam to the beginning of the Holstein-Friesian Herdbook, was tabulated for each of these 1800 females. These were used to estimate inbreeding and inter se relationship for the Holstein breed. Estimates of inbreeding were 4.7, 3.8, and 4.3% for 1970, 1976, and 1982. These estimates were not different from one another or from 1928 and 1931 estimates. Estimates of inter se relationship were 5.2, 7.3, and 9.8% for 1970, 1976, and 1982. These estimates were different from one another and from an estimate of 3.4% for 1931. The increase in inter se relationship without corresponding increase in inbreeding indicates that a change in mating strategies has evolved over time. The majority of breeders now apparently mate animals that are less related than if mating was random, whereas in the past there was more of a tendency to mate within the same line. Despite these attempts to avoid inbreeding, it may be only a matter of time until increasing inter se relationship causes an increase in inbreeding. Because of detrimental effects associated with inbreeding, it is important that the Holstein breed be monitored on a regular basis for these parameters. Ancestors that occurred most frequently in the 1982 sample were identified and their direct relationships to the breed tabulated for the years studied.