PATHOGENICITY OF DAILY INTAKES OF COOPERIA-ONCOPHORA LARVAE IN GROWING CALVES

Groups of three 4 1 2-month-old calves were offered a complete ruminant diet ad libitum and given, on 5 days each week for 20 weeks, either 0, 5000, 10 000 or 20 000 Cooperia oncophora larvae. All calves were killed 2 weeks after recieving the last dose of larvae. Cooperia infection reduced liveweight gain by 13.5% but did not significantly affect voluntary dry matter intake or produce any obvious clinical signs. No relationship was evident between the rate of larval intake and worm burden or faecal egg count. It appeared that a degree of acquired resistance developed in the majority of infected calves by 8-10 weeks. At slaughter, early fourth stage larvae predominated in four calves and maximum worm recoveries from the intestine were only 1.5% of the total larval intake. The majority of Cooperia were located in the duodenum and anterior jejunum. Pathological changes were restricted to areas surrounding the worms and consisted only of compression and distortion of villi in contact with parasites. Slight hypoalbuminaemia occurred between weeks 7 and 13 post inoculation in the group which received 20 000 larvae/day. There were no significant effects on serum total protein, globulin, urea, calcium, magnesium or phosphorus concentrations, or skeletal composition. © 1979.