Experimental studies on the interaction between infections ofOstertagia leptospicularis and other bovineOstertagia species

Experimental infections of calves were carried out with either isolates of predominantlyOstertagia ostertagi, pureO. leptospicularis or a mixed isolate of equal numbers of both these species. The total worms established on day 21 for the mixed species from a total inoculum of 100000 infective larvae, was 1.2 times greater than from 100000 larvae of theO. ostertagi isolate and 3.3 times that of the pureO. leptospicularis isolate. The increased establishment in the mixed inoculum referred to bothO. ostertagi andO. leptospicularis (days 17 and 21). These differences were both highly significant (P<0.01). The severity of the pathological changes was also greater in the mixed infections. It is suggested that these findings must be taken into account when control measures involving alternate grazing of sheep and cattle are being employed.