Document Type


Publication Date



Veterinary Department

Circular Number



veterinary, vet, internal parasites, sheep


Parasitism is the worst hazard in the raising of sheep. This is true in South Dakota and is generally true in other sheep-raising areas. No accurate figure of the cost of worm infestations can be given. The cost includes the loss in deaths, the lowered values of the unthrifty, light-weight lambs which survive, the added expense in feed and time in making such lambs salable, the cost of worm treatments and time in administering them. To these costs should be added the weight loss by sheep, resulting from moving them from range for treatments, and the handling of the flock incident to treatment. If figures were available, the total annual loss to sheep growers would certainly be many thousands of dollars in South Dakota alone. There has been a marked increase in numbers of sheep in the state in the past twenty-year period, from 682,000 in 1925 to a high of 2,300,000 in 1944. An increase in numbers on some farms and ranches without corresponding increase in acreage for pasture has no doubt contributed greatly to the seriousness of the parasite problem. There was a decline of 26 per cent in numbers of sheep in the two years preceding January 1, 1946.2 Difficulty experienced in controlling internal parasites is undoubtedly one of the factors responsible for the decrease. Some flocks were reduced in numbers and some were sold, entirely because of this difficulty. A study was undertaken in 1943 with the ultimate purpose of finding means of reducing the loss from parasites.3 The work has been confined largely to the range areas of the northwestern counties. It has included field observations of flock and range management methods, examination of sheep for evidence of parasitic infestations, and postmortem examinations for the various kinds of worms. During the 1945 grazing season an experimental flock was maintained under range conditions for study of the parasite problems










South Dakota State College of Agriculture and Mechanic Arts, Agricultural Experiment Station