A Holstein herd at Iowa State has been closed to outside blood for about 30 years. Here are some developments to date regarding the effect of selection and the results of mild inbreeding that occured in the herd.
Freeman, A. E.
"A Situation Report - Iowa State's "Closed" Dairy Herd,"
Iowa Farm Science: Vol. 17
, Article 4.
Available at: https://lib.dr.iastate.edu/farmscience/vol17/iss3/4