Table 1.

EPG data from day of slaughter and estimated numbers of adult worms recovered in 20 ml subsamples at necropsy, from calves before and 10 days after injection with ivermectin (Ivomec®, Merial) at a dose rate of 0.2 mg IVM/kg

Treatment	Calf	Origin	O. ostertagi		C. oncophora		EPG
			Males	Females	Males	Females
Before IVM	A1	TiHo	2,070	3,230	6,470	5,270	750
	B1	Gråmunkehöga	570	670	9,070	13,600	1,000
	C1	Kolsta	900	2,900	1,930	3,070	400
After IVM	A2	TiHo	0	0	3,330	5,730	150
	A3	TiHo	0	0	130	400	<50
	B2	Gråmunkehöga	0	0	6,000	6,200	50
	B3	Gråmunkehöga	100	0	200	200	<50
	C2	Kolsta	0	0	600	1,600	<50
	C3	Kolsta	0	0	1,000	2,000	<50

Calves were previously each inoculated with a mixture of 40,000 L3 of C. oncophora and O. ostertagi, representing isolates with different deworming history. Calves A1, A2 and A3 were inoculated with equal mixtures of laboratory-maintained C. oncophora and O. ostertagi from TiHo, whereas B1, B2, B3, C1, C2 and C3 were inoculated with cattle nematodes from two different farms in Uppland, Sweden, showing phenotypic clinical IVM resistance in previous field trials. Ten worms from each calf were immediately recovered and stored separately at −80 °C for RT-qPCR, and excessive worms were stored at −20 °C for AFLP analysis