The deposition of dung on pasture may create a trade-off between the benefit of increased nutrient intake due to the leaching of nutrients and the risk of parasitism due to migration of helminth parasite larvae (Sykes, 1987), from the faeces to the sward. Physiological state can affect herbivore foraging decisions in relation to this trade-off. Our objectives were to determine whether such a trade-off exists in a grazing situation for sheep and whether level of feeding motivation and parasitic status affect the grazing behaviour of sheep faced with this trade-off.

Texel x Greyface lambs were presented pairs of swards (36 x 21cm) which varied in nitrogen content (high=N+; low=N-) and level of contamination with faeces from sheep infected with Ostertagia circumcincta (Ost.) (20g faeces per sward=F+; no faeces=F-) and allowed to graze for short periods (60 bites or ten minutes). We defined ‘taking the trade-off’ as taking more bites from an N+F+ sward compared to an N-F- sward, when presented together as a choice.