able climatic factors on the various stages of parasites. 1/ 
About 300 kinds of internal parasites are of economic impor= 
tance to the livestock industry of the United States. Some of 
these parasites are very common and abundant, others extremely 
rare. 2/ Few animals are ever entirely free from them; many 
are the hosts of several thousand parasites, comprising a dozen 
or more injurious species. Losses occur in animals of all ages, 
but are heaviest in young stock, chicks, and turkey poults,. 
The specific ways in which losses are sustained on account of 
livestock parasites are legion, but a consideration of some of 
them, as outlined below, will emphasize the difficulty, if not 
impossibility, of arriving at accurate estimates, as well as 
the reasons for regarding all presently available information, 
however carefully assembled, as fragmentary. 
Mortality Losses 
Death losses of breeder, or farm, stock and of stock produced 
for market, 
Morbidity Losses 
(1) Reduced yield and depreciation of animal products--milk, 
eggs, hides, wool, mohair, casings, medicinal prepara- 
tions. 
(2) Condemnations of parts and carcasses under Federal or 
other meat inspection procedure. 
(3) Waste of feed, labor, and space to bring animals to 
productive or useful maturity or to market. 
(4) Interference with breeding and reproduction--sterility, 
diminished fertility and vigor, delayed conception, 
abortion, reduced litter size, lowered egg laying of 
chickens. 
(S) Reduced quality of animals--lowered grades of market 
stock, reduced sale value, 
1/ Lucker, John T. 1941, Climate in relation to worm parasites 
of livestock. In Climate and Man, 1941 Yearbook of Agriculture, 
pp. 517-527. 
2/ Dikmans, G. 1945. Check list of the internal and external 
animal parasites of domestic animals in North America. Am. Jour. 
Vet. Res. 6(21): 212-241. 
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