Table 1 Number of cows, average ± standard deviation of anti- O. ostertagi antibody levels in individual milk before treatment registration and distribution of breed, lactation number and year quarter of calving in the treated and untreated group

Number of cows

234

243

Anti- O. ostertagi antibody level (ODR)

0.49 ± 0.3

0.52 ± 0.3

Breed (%):

Holstein Friesian

43

46

Other

6

5

Lactation number (%):

First

14

12

Second

13

13

Third or higher

26

22

Year quarter:

Jan - Mar

10

14

Apr - Jun

13

8

Jul - Sep

13

12

Oct - Dec

15

15