Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
Accounts of scrapie have been published in northwestern Europe since 1750. Available evidence suggests the prevalence and occurrence of scrapie is closely connected with the breed and genetic structures of the sheep population to which the affected animals belong. After 1700, ovine nutritional and environmental housing conditions improved in Europe with the exception of Spain. Interest in phenotype improvement by genetic selection began at this time also, leading to a system of closer inbreeding. The Spanish merino studs of Germany and France in the late eighteenth century adopted a program of closer inbreeding with catastrophic results. Within 20 years, scrapie had become so prevalent that certain stud flocks were almost lost, as losses from this disease outnumbered increases in the herd. Without individual animal identification and well kept mating and lambing records, it was difficult to control any genetic predisposition to this disease. This is especially true with scrapie, which does not manifest itself until middle age, often halfway through an animal's reproductive life. Unfortunately such records were not always kept under European 18th century farming conditions.
VanderGaast, Nadia E. and Miller, L. D.
"A Brief Review of Scrapie,"
Iowa State University Veterinarian: Vol. 52
, Article 4.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol52/iss1/4