Selected epizootiologic aspects of bovine leukemia in Minnesota (1961-1965)
Anderson, R.K.; Sorensen, D.K.; Perman, V.; Dirks, V.A.; Snyder, M.M.; Bearman, J.E.
American Journal of Veterinary Research 32(4): 563-577
1971
ISSN/ISBN: 0002-9645 PMID: 5170857 Document Number: 35135
From 1960-65 (inclusive) veterinarians were asked to complete questionnaires and furnish samples for all suspected cases. A project veterinarian examined each case. The statistical significance and shortcomings of the survey were discussed, and data are presented fully. A total of 2, 152 cases was reported, and more than 40% confirmed, i.e. 178 per year, or 14.8 per 100, 000 dairy cows at risk, and this would represent a minimal value. Most statistics related to dairy cows of two years or more, which comprised 87% of the total confirmed cases. Incidence rates apparently declined in 1964 and 1965. They were highest in January and lowest in December, but seasonal differences were not significant. Countries with a high dairy population density had high incidence rates. In herds greater than 19 head, incidence rates doubled for every 10 head increase in size up to 50 head, suggesting an infective or viral agent. Incidence rates doubled between age groups 2-5 years and 6-9 years, indicating a build-up of predisposing factors, e.g. radiation, pesticides, food additives. Purebred cattle (particularly Guernsey and Brown Swiss breeds) were comparatively resistant; Guernsey and Brown Swiss crosses were fairly resistant, but crosses with predominantly Holstein-Friesian, Jersey or Milking Shorthorn blood were particularly susceptible.