Epidemiological studies on Ostertagia ostertagi infections in cattle during their first, second and third summer on...

The number of Ostertagia ostertagi in the abomasum of steers, that had been on pasture for one, two or three summers was determined. A total of 44 animals were examined and of these 12 had been out one summer 27 two summers, and five during three summers. During the grazing seasons plasma pepsinogen and serum albumin was determined on all the steers and on 24 heifers during their first summer on pasture. The mean number of parasites in the abomasum after one summer was 128,500 and at the end of the second summer 2,400 and after the third 800. In animals slaughtered in February after housing in October the first year the mean number was 33,300 with 29,900 arrested L4-larvae. During the first summer on pasture there was a strong rise in the plasma pepsinogen values until the beginning of August. This rise reflected the infection rate. Also after turning out the second and third summer a rise in plasma pepsinogen was noted but now with shorter duration. This rise was probably caused by liberation of arrested L4-larvae from the preceding year. The serum albumin values decreased in all animals after turning out. However, the decrease was strongest the second and third summer when the parasite number was low. This indicates that also other factors than parasites influence the serum albumin level.