Influence of Miles City Line 1 on the United States Hereford population1,2,3

relationship between L1 and the general Hereford population recorded by the AHA. In a second experiment, 5 sets of 400 animals were drawn from the AHA herdbook representing each year from 1980 to 2008 and pseudo mated to L1 sires and their relationship to L1 calculated as described above. Over the period, the number of animals recorded by the AHA that were related to L1 increased by 1.69 ± 0.07% per year. The L1 Hereford population was ancestral to 79% of Hereford cattle recorded in 2006 through 2008. The greatest concentration of animals related to L1 was in the Great Plains and eastern Corn Belt of the United States, but animals related to L1 were found in 48 states. In a third experiment, 240 L1 Hereford cattle and 311 sires representative of the Hereford breed in the United States were genotyped using the Illumina BovineSNP50 BeadChip. Resulting genotypes were used to assess the probability that the animals sampled from the U.S. population were members of L1. The average probability of membership in L1 was 0.20 and the regression of genomic probability of membership on pedigree relationship was 1.73 ± 0.11 (r = 0.65). These results document the far-reaching and profound impact of a long-term research program.