Faecal avoidance in Romney sheep lines selected for resistance or resilience to gastro-intestinal nematodes

Abstract

Faecal avoidance was assessed in Romney lambs from lines selected for resistance or resilience to gastro-intestinal nematode parasites. Ten lambs from each selection line that were maintained in separate farmlets and naturally exposed to parasites were assessed on distance grazed from either a mud-clay or faecal ball at 130, 150, 180 and 210 days-of-age. Resistant line animals maintained lower faecal-egg counts compared with resilient lambs, viz. 25.6 c.f. 771.0 eggs per gram of faeces (P<0.001) and greater Trichostrongylus colubriformis-specific immunoglobulin G absorbance (P=0.005) indicating differences between selection lines in parasite loading and immunlogical status. Grazing distance from the object was greatest for faecal ball, viz. 11.53 ± 1.14 cm compared with mud-clay ball, viz. 4.19 ± 1.00 cm (P<0.001) and decreased with time (P<0.001). Grazing distance tended to be greater for resilient, viz. 8.63 ± 1.14 cm than resistant, viz. 7.09 ± 0.99 cm (P=0.09) but there was no interaction between selection line and ball type (P=0.709) indicating similar levels of faecal-specific aversion between the selection lines. These results suggest that the lesser infection levels in resistant-line animals when grazing is unlikely to be due to reduced exposure to infective larvae as a consequence of greater faecal avoidance.