Influence of Miles City Line 1 on the United States Hereford population

The goal of this research was to document the influence of Line 1 (L1) Hereford cattle, developed by the USDA at its research facility in Miles City, MT, on the U.S. Hereford population. The L1 Hereford population originated in 1934 and has been thereafter maintained as a closed herd at that location. Dissemination of germplasm began in 1948. Pedigree data for approximately 14 million cattle recorded by the American Hereford Association (AHA) were used. A preliminary experiment was conducted to establish sample size necessary to estimate the pedigree relationship between L1 and the recorded Hereford population. Five random samples of 100, 400, 500, and 3,000 calves were drawn from the sets of calves born in 1980, 1990, and 2000. Sampled calves were pseudo mated to L1 sires from the decades 1968 to 1978, 1978 to 1988, and 1988 to 1998, respectively. Inbreeding coefficients were calculated for the resulting "offspring" and the relationship of each sampled animal to L1 was taken to be twice the maximum inbreeding coefficient for the set of L1 sires used in the pseudo matings. Based on the results of this experiment, it was decided that a sample size of 400 animals per replicate was sufficient to estimate the 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.