Much of the loss from both diseases and parasites is preventable 
by known means, and much more can presumably be prevented by fur- 
ther research. 3/ 4/ This conviction is probably the basis of a 
recent estimate that preventable losses may amount to about 10 per- 
cent of the annual value of livestock production, or a loss that 
may conservatively be said to amount to over $2 billion. About 
half of this may be ascribed to parasites, of which there are ex- 
ternal as well as internal species. 
Among the principal objectives of the estimates in Table 25 of 
losses due to individual internal parasites were conservatism 
and reliability, and an examination of the over-all picture out- 
lined above suggests that these estimates may be far too low. In 
general, mortality and morbidity losses were well considered, whate 
ever degree of accuracy may have been attained. On the other hand, 
losses due to control expenditures were not included, except for 
a few parasites affecting horses and poultry. 
The major items considered were (1) kinds or categories of 
parasites affecting each class of livestock; (2) their occurrence, 
distribution, and relative capacities for causing economic loss; 
(3) the nature of economic losses from parasites; (lh) the ways 
in which the individual parasites injure their hosts; (5) esti- 
mates by the croperenporting sarvices of total disease and parasite 
lesses 5/ 6/3 (46) of ficial. data on populations and value ef annual 
production of the several classes of livestcck in the United 
States; and (7) individual jndements of arthorities on the com- 
parstive importencea of diseases and parasites as causative factors 
of economic loss amons the several classes of livestock, 
Insect Pests of Livestock and Poult 
(Table 26) 
The abundance of several of the livestock insect pests varies 
little from year to year. Weather may shorten or lengthen the 
active season of biting flies, but on a countrywide basis live- 
3/ Foster, A. O. 1951. Internal parasites of livestock. Proc.. 
U. N. Sci. Conf. on Conserv. and Util. Resources (199), v. 6, 
Land Resources, pp. 81-1:85. 
h/ Foster, A. 0. 1953. Critical review of present-day treatments 
of parasitic infections, giving lists of drugs. Proc. XV Internatl. 
Vet. Cong. ; Ve 1; pt. 1; pp. 4) 58=1:68. 
5/ Mohler, John R.,et al. 1942. Losses caused by animal diseases 
and parasites. In Keeping Livestock Healthy, Yearbook of Agriculture 
1942, pp. 109@116,. 
6/ Nordquist, A. V. 1947. Estimating livestock losses. Proc. 
SOth Meeting of U. S. Livestock Sanitary Assoc. 196, pp. 199-208. 
= 150) 
