Invited review: research contributions from seventy-five years of breeding Line 1 Hereford cattle at Miles City, Montana.

For 75 yr, Line 1 Hereford cattle have been at the forefront of beef cattle breeding research. The goal of this review is to provide an overview of scientific contributions made using the Line 1 Hereford population. It was initially developed as contribution to a western regional program from which beef producers were envisioned to use heterosis by crossing selected inbred lines. Whereas this vision was never fulfilled, being largely supplanted by crossbreeding, Line 1 has had a profound influence on beef cattle breeding research and the Hereford breed. For more than 60 yr, Hereford breeders and commercial beef producers have purchased Line 1 Hereford germplasm for use in their herds. By example, Line 1 illustrates a successful line-breeding program through which a 39% additive relationship to the founding sire has been maintained over more than 18 generations. Procedures for performance testing beef cattle can be traced to original research with Line 1. Data from Line 1 contributed to the first estimates of heritability and genetic correlation for beef cattle. Work with Line 1 has also contributed greatly to the understanding of maternal genetic effects in beef cattle. Diallel crossing with other inbred lines provided early estimates of heterosis for beef cattle, complimented by the later observation that heterosis resulted in complete recovery of the accumulated negative effects of inbreeding. After exchanges of germplasm with the Northern Montana Agricultural Experiment Station at Havre and the Brooksville Beef Cattle Research Station in Florida, pioneering comprehensive evaluations of genotype x environment interaction were conducted. Breeding practices implemented by USDA Agricultural Research Service at Miles City make Line 1 the longest running selection experiment using beef cattle worldwide. This long-term database has provided an exceptional resource for prototype evaluations of procedures for national cattle evaluation, and the results make up an integral part of the foundation of modern-day genetic evaluation programs. Having used DNA from Line 1 in the development of a bacterial artificial chromosome library and the bovine genome sequence, Line 1 Hereford cattle are uniquely positioned for continued contributions in future research.