Do the changes in the behaviours of cattle during parasitism with Ostertagia ostertagi have a potential diagnostic value?

We investigated the magnitude of temporal changes in activity, posture and feeding behaviour of cattle infected with Ostertagia ostertagi, and their reversal after treatment with an anthelmintic. Twenty-six, 3-month-old, Holstein-Friesian bulls were allocated to one of three treatment groups. Bulls in two of those (groups P and PA) received 100,000 larvae on three occasions (Days 0, 7 and 14) and the remaining animals served as controls (C). The PA group also received an anthelmintic on Day 31. Parasite eggs appeared in the faeces of P and PA bulls from Day 17; from approximately the same time blood pepsinogen levels increased and body weight (BW) gain decreased (P < 0.001). The reduction in BW gain persisted until Day 45 for P animals only. There was a decrease in the number of steps taken for P and PA animals, as well as lying and standing episode frequency, by 41 and 44% respectively (P < 0.001) from Day 21 onwards. The average lying and standing episode duration increased by 52 and 55% respectively (P < 0.001) from the same time in P and PA compared to C bulls. In addition, meal frequency showed a tendency to decrease for P animals only (P = 0.039) from Day 39, and this was the only aspect of feeding behaviour affected by parasitism. All behaviours, returned to control levels within a week of anthelmintic drenching of PA bulls, apart from the number of steps taken. Although BW gain and pepsinogen also started to recover after drenching, these had not returned to control levels by Day 45. The magnitude of the changes in activity, and standing and lying episode frequency and duration suggest that these might have a diagnostic value, especially as all can now be monitored by automated means. However, these behaviours did not show the rapid changes we expected before parasitism manifested clinically and following recovery.