Association of blood eosinophilia with the expression of resistance in Romney lambs to nematodes

The dynamics of blood eosinophilia was studied in Romney lambs dosed twice weekly with 5000 infective larvae of Trichostrongylus colubriformis. A marked rise in blood eosinophil counts of the dosed lambs coincided with the start of the decline of faecal egg counts (FEC). Eosinophilia was also studied in grazing Romney lambs from a breeding programme, based on selection for high or low FEC. Comparison of the sire groups suggested that the magnitude of the eosinophil response was under genetic control. The significant negative correlations between blood eosinophil counts and FECs confirmed the association between eosinophilia and the expression of resistance in Romney lambs to nematodes. However, comparison of the mean blood eosinophil counts and FECs for both the ram and ewe lambs of the resistance sire groups suggested that the association of eosinophilia and resistance may be greater for some sire groups than others.