ESTIMATES OF INBREEDING AND RELATIONSHIP AMONG REGISTERED HOLSTEIN FEMALES IN THE UNITED-STATES

The estimate of inbreeding for registered Holstein females born during 1990 was 5.1 +/- 0.4% for a random sample of 600 two-line pedigrees. Previously published estimates were 4.7% for 1970, 3.8% for 1976, and 4.3% for 1982 from similar samples of pedigrees. These estimates were calculated using a base of approximately 1884, or the initiation of he rd-book registration in the US. The estimate of relationship between r andomly paired females born during 1990 was 10.2 +/- 0.8%; relationshi ps were 5.2% for 1970, 7.3% for 1976, and 9.8% for 1982. Average relat ionship within the breed increased significantly without a correspondi ng increase in inbreeding. Inbreeding was also estimated for alternati ve base years with 10-yr increments to determine the effect of base ye ar on estimates of inbreeding. Using 1950 as the base year, inbreeding was estimated at 0.5% for 1970, 0.3% for 1976, 1.6% for 1982, and 2.1 % for 1990. Estimates using 1920 as the base year were 2.0% for 1970, 1.9% for 1976, 2.3% for 1982, and 3.2% for 1990. More recent base year s gave lower estimates of inbreeding, as expected, but showed an exagg erated percentage of increase in inbreeding from 1970 to 1990. However , the annual amount of increase of inbreeding from 1976 to 1990 was no t significantly affected by time of base year and ranged from 0.08 to 0.12/yr. The five most influential bulls of the breed were Pawnee Farm Arlinda Chief 1427381, Round Oak Rag Apple Elevation 1491007, S-W-D V aliant 1650414, Osborndale Ivanhoe 1189870, and Sir Pietertje Ormsby M ercedes 44931; estimated direct relationships to the breed were 0.123, 0.122, 0.096, 0.083, and 0.074, respectively.